Effect of Cr and Co Promoters Addition on Vanadium Phosphate Catalysts for Mild Oxidation of n-B

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NiFe-MOF衍生的Fe掺杂Ni基硒化物作为高效的析氧催化剂

第49卷第22期2021年11月广州化工Guangzhou Chemical IndustryVol.49No.22Nov.2021NiFe-MOF衍生的Fe掺杂Ni基硒化物作为高效的析氧催化剂*王天河，黄亭亭，秦子菁，任威威，蒋庆，唐文强，谢华明，雷英(四川轻化工大学化学工程学院，四川自贡643000)摘要：发展高效、耐用的析氧反应(OER)电催化剂是大规模电解水的关键。

本文以多孔网络结构的NiFe双金属有机骨架(MOFs)为前驱体，通过水热硒化过程，定向转化成纳米团簇结构的NiFe硒化物。

其中，Ni0.67Fe0.33Se在1.0M KOH电解质中显示极低的过电位(297mV)和较小的Tafel斜率(55.0mV/dec),12h测试过程中保持了良好的稳定性。

关键词：析氧反应；金属有机骨架；NiFe硒化物；水热法.中图分类号：0657.3文献标志码：A文章编号：1001-9677(2021)022-0030-04 NiFe-MOF Derived Fe-doped Ni-based Selenides for EfficientOxygen Evolution Catalysts*WANG Tian-he,HUANG Ting-ting,QIN Zi-jing,REN Wei-wei,JIANG Qing,TANG Wen-qiang,XIE Hua-ming,LEI Ying(College of Chemical Engineering,Sichuan University of Science&Engineering,Sichuan Zigong643000,China) Abstract:The development of high efficient and durable electrocatalyst for oxygen evolution reaction(OER)is the key technology for large-scale industrial water splitting.NiFe bimetallic organic frameworks(MOFs)with porous network structure were used as precursors to be directionally transformed into NiFe selenides with nanocluster structure via hydrothermal selenization process.Among them,Ni067Fe033Se exhibited very low overpotential(297mV)and small Tafel slope(55.0mV/dec)in1.0M KOH electrolyte,and maintained good stability during overall12h test.Key words：oxygen evolution reaction；metal organic framework；NiFe selenide;hydrothermal method随着绿色、可持续和可再生能源氢能源越来越受到关注，产氢、储氢以及氢能转化技术等成为研究热点电化学水裂解是一种极有前途的清洁产氢方法，然而析氢过程伴随着的动力学缓慢的析氧反应(OER)却限制了水裂解过程⑵。

Fischer–Tropsch synthesis over alumina supported cobalt catalyst Effect of crystal phase and pore

Journal of Molecular Catalysis A:Chemical 394(2014)22–32Contents lists available at ScienceDirectJournal of Molecular Catalysis A:Chemicalj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /m o l c a taFischer–Tropsch synthesis over alumina supported cobalt catalyst:Effect of crystal phase and pore structure of alumina supportKatsuya Shimura ∗,Tomohisa Miyazawa,Toshiaki Hanaoka,Satoshi HirataBiomass Reﬁnery Research Center,National Institute of Advanced Industrial Science and Technology (AIST),Kagamiyama 3-11-32,Higashihiroshima,Hiroshima 739-0046,Japana r t i c l ei n f oArticle history:Received 28April 2014Received in revised form 24June 2014Accepted 27June 2014Available online 4July 2014Keywords:Fischer–Tropsch synthesis Cobalt AluminaCrystal phase Pore structurea b s t r a c tEffect of crystal phase and pore structure of Al 2O 3support was examined in order to improve the activity of Co/Al 2O 3catalysts for FT synthesis.Total 18kinds of Al 2O 3supports having different crystal phase and pore structures were prepared by the calcination of commercial boehmite and gibbsite under various conditions.Cobalt was loaded on these Al 2O 3supports by the impregnation,drying and calcination.Activity of Co/Al 2O 3catalyst for FT synthesis was evaluated with a continuously stirred tank reactor.Structure of Co particles and activity of Co/Al 2O 3catalysts strongly depended on the pore structure (i.e.surface area and pore size)of Al 2O 3support rather than the crystal phase.Among the examined samples,the highest activity was obtained over the catalyst,which was prepared from ␪-Al 2O 3having the moderate surface area (84m 2g −1).When Al 2O 3supports having the moderate surface area were used,the formation of Co particles having high dispersion and relatively uniform size was promoted by pores of suitable size and led to the enhancement of overall catalytic activity.©2014Elsevier B.V.All rights reserved.1.IntroductionIt is highly desired to establish practical methods of producing clean alternative fuels in the near future due to the growing con-cern of environmental and energy problems.Fischer–Tropsch (FT)synthesis,which can synthesize hydrocarbon mixtures from syn-gas,is an excellent way to produce liquid fuel,since various carbon sources (e.g.coal,natural gas and biomass)can be used as feed-stock [1,2].Furthermore,liquid fuels produced by FT synthesis do not contain any sulfur,nitrogen and aromatic compounds.There-fore,FT synthesis has attracted renewed attentions as one of the production methods of liquid fuels.So far,various attempts such as development of catalysts and reactors have been made in both academia and industry to enhance the efﬁciency of this reaction system.Catalysts employed for FT synthesis are some heteroge-neous transition metal ones such as Fe,Co,Ni and Ru.Among them,Co-based catalysts are advantageous to the practical application due to the relatively high activity and selectivity to long-chain liner hydrocarbons,high resistance toward deactivation,low activity for the competitive water-gas shift reaction and lower price than Ru [3,4].Since activity of supported Co catalysts generally depends∗Corresponding author.Tel.:+81824208292;fax:+81824208292.E-mail address:katsuya-shimura@aist.go.jp (K.Shimura).on the number of exposed Co metal atoms [5–7],Co is usually deposited on supports having high surface area (e.g.SiO 2,Al 2O 3,TiO 2and carbon materials)in order to improve the dispersion of active Co metal species [1–4].Alumina is one of the most employed supports for Co-based FT catalysts due to the high thermal stability and the strong resistance to attrition.Al 2O 3support may also contribute to a stable catalytic activity for a long time,since the great ability of Al 2O 3support to stabilize small metal clusters would suppress the aggregation of Co metal particles during the catalytic reaction.However,the strong interaction between Co particles and Al 2O 3support often makes the reduction of Co oxide difﬁcult and reduces the number of active Co metal species,resulting in the suppression of the activity of Co/Al 2O 3catalyst.Thus,small amount of noble metal (e.g.Pt [8–10],Re [8,9,11],Ru [8,9,12],Pd [9,13],Ir [14],Au [15,16]and Ag [15,17])is often added to Co/Al 2O 3catalysts,since noble metal additives can promote the reduction of Co oxide species and increase the number of active Co metal sites,presumably by hydrogen disso-ciation and spillover from the promoter surface.However,noble metals are not suitable to the industrial application due to their high cost.Therefore,various examinations are currently carried out,such as the development of more inexpensive promoters (e.g.Zr,alkali earth elements and rare earth elements)and the improve-ment in the preparation method of Co/Al 2O 3catalysts and so on [1–4]./10.1016/j.molcata.2014.06.0341381-1169/©2014Elsevier B.V.All rights reserved.K.Shimura et al./Journal of Molecular Catalysis A:Chemical394(2014)22–3223The physicochemical properties of Al2O3support such as pore size[18–20],crystal phase[21–25],morphology[26–30]and acid–base property[31,32]also inﬂuenced the structure of Co parti-cles and the activity of Co/Al2O3catalyst.For example,it is generally accepted that Co particle size depends on the pore size of Al2O3 support and large Co particles tend to be formed on the Al2O3sup-port having large pore size[18–20].Holmen et pared four kinds of Co/Al2O3catalysts,which were prepared from Al2O3sup-ports having different crystal phase(␣,␥,␦and␪).They found that Co/Al2O3catalyst prepared from␣-Al2O3showed the high-est selectivity of C5+products[21–23].Panpranot et al.reported that Co/Al2O3prepared from␹-Al2O3showed better catalytic per-formance than that prepared from␥-Al2O3[24,25].Martínez et al. applied the nanoﬁbrous␥-Al2O3as the support material along with several commercial Al2O3[28].They found that activity of CoRu/Al2O3catalysts depended on the support surface area rather than the pore size and CoRu/Al2O3catalyst prepared from nanoﬁ-brous␥-Al2O3showed the highest activity.Sun et al.examined the impact of acid–base property of Al2O3support on the catalytic activity[31,32].They found that Al2O3support with low acidity showed high catalytic activity due to having the high reduction degree of Co.Although the catalytic activity strongly depended on the structure of Al2O3support as described above,inﬂuence of the structure of Al2O3support on the activity of Co/Al2O3catalyst for FT synthesis is not fully understood yet.In the present study,we examined the effect of crystal phase and pore structure of Al2O3support on the activity of Co/Al2O3cat-alyst for FT synthesis.Al2O3supports having different crystal phase and pore structures were prepared by the calcination of commer-cial boehmite and gibbsite at various temperatures,and Co was loaded by an impregnation method using Co nitrate as the Co pre-cursor.The activity of prepared Co/Al2O3catalysts for FT synthesis was evaluated with a continuously stirred tank reactor.We sys-tematically examined the relationship between the structure of Co particles and the activity of Co/Al2O3catalysts in order to obtain the catalyst design concept.2.Experimental2.1.Catalyst preparationAl2O3supports having different crystal phase and pore struc-ture were prepared by the calcination of commercial boehmite (AlO(OH)·n H2O,Wako)and gibbsite(Al(OH)3·n H2O,Merck)in air under various conditions(600–1050◦C,3–10h).Al2O3supports prepared from boehmite and gibbsite were referred to as Al-B(calcination temperature,calcination time)and Al-G(calcination temperature,calcination time),respectively.One commercial␥-Al2O3purchased from Soekawa chemical(named Al-S)was also used as comparison.Co-loaded Al2O3(named Co/Al2O3or Co/Al)catalysts were pre-pared by an impregnation method using Co(NO3)2·6H2O(99.5%, Wako)as Co precursor.Loading amount of Co was20wt%for all samples.In the impregnation method,Al2O3powder(8.0g)was dispersed into an aqueous solution(100ml)of Co nitrate and stirred for0.5h,followed by evaporation to dryness at90◦C.Then,the obtained powder was dried at100◦C for12h and calcined in air at 400◦C for3h.2.2.CharacterizationN2adsorption/desorption isotherms of the samples were mea-sured at−196◦C using a BERSORP-miniII equipment(BEL Japan Inc.).Prior to the measurements,the samples(0.15g)were out-gassed at105◦C for6h under vacuum.The speciﬁc surface area was obtained by applying the Brunauer–Emmett–Teller(BET)model [33]for absorption in a relative pressure range of0.05–0.30.The total pore volume was calculated from the amount of N2vapor adsorbed at a relative pressure of0.99.The pore size distribution of the samples was determined by the BJH(Barrett–Joyner–Halenda) model[34]from the adsorption branches of the nitrogen isotherms. According to the IUPAC classiﬁcation,all samples exhibited the type H3shaped hysteresis loop[35].This suggests that Al2O3supports and Co/Al2O3catalysts prepared in the present study have slit-type pores,which are associated with the interparticle voids generated in solids with plate orﬁber-like morphology.Powder X-ray diffraction(XRD)pattern was recorded at room temperature on a Rigaku diffractometer RINT2500TTRIII using Cu K␣radiation(50kV,300mA).The mean particle size of Co3O4 (d Co3O4)was calculated from the diffraction line at2Â=36.9◦with the Scherrer equation.The obtained particle size of Co3O4could be used to calculate that of Co metal(d Co)after hydrogen reduction pretreatment by the following formula(Eq.(1))[10].d Co=0.75×d Co3O4(1)Temperature programmed reduction under H2(H2-TPR)was carried out with BELCAT-B(BEL Japan Inc.).The calcined catalyst (0.10g)was mounted in a quartz cell and heated up to900◦C in a ﬂow of5%H2/Ar(30ml min−1).The heating rate was10◦C min−1. The reduction degree of supported cobalt was calculated from the amount of H2consumption during H2reduction pretreatment at 400◦C for6h.The efﬂuent gas was passed through a5A molecular sieve trap to remove the produced water before reaching a thermal conductivity detector.Hydrogen chemisorption experiments were performed on BELCAT-B.Before measurement,the samples were reduced at 400◦C for6h in aﬂow of5%H2/Ar(15ml min−1)and held at 400◦C for1h in aﬂow of Ar(30ml min−1)to desorb the residual chemisorbed hydrogen.After cooling the sample down to100◦C in aﬂow of Ar,H2chemisorption measurements were started.Cor-rected dispersion(D corr,Eq.(2))and surface area of Co metal were calculated according to the method reported in literature[36].D corr=(number of surface Co metal atoms)(number of total Co atoms)×(fraction reduced)×100(2)Transmission electron microscopy(TEM)images of the reduced and passivated Co/Al2O3catalysts were recorded by a JEOL electron microscope(JEM-3000F,300kV)equipped with energy dispersive X-ray spectroscopy(EDS).The amount of sodium included in the Al-B(600,3)and Al-G(600, 3)supports was measured by inductively coupled plasma atomic emission spectroscopy(ICP-AES).The samples were dissolved in nitric acid solution before analysis.2.3.Typical procedures of catalytic reactionsFT synthesis was performed with a continuously stirred tank reactor in a similar way to the previous study[37].Before reaction, catalyst(2.5g)was in situ reduced in aﬂow of H2(40ml min−1) at400◦C for6h.After the reactor was cooled down to room tem-perature and purged by N2gas,n-hexadecane(80g)solvent was added.Then,the reaction was carried out at230◦C and1.0MPa for 8h in aﬂow of synthetic gas(100ml min−1).The syngas used for this reaction was obtained by the gasiﬁcation of woody biomass, followed by the gas puriﬁcation and the composition adjustment [38].Composition of this biomass-derived syngas was conﬁrmed by gas chromatography(GC)as follows:H2(59.9%),CO(29.8%),CH4 (5.0%),N2(4.9%)and CO2(0.4%).The efﬂuent gas after FT synthesis was analyzed by on-line GC.A thermal conductivity detector(TCD) with a Porapak-Q column was used to analyze inorganic gases(H2, CO,CO2,CH4and N2).Light hydrocarbons(C1–C4)were analyzed by24K.Shimura et al./Journal of Molecular Catalysis A:Chemical 394(2014)22–32a ﬂame ionization detector (FID)with a RT-QPLOT capillary column.Hydrocarbons dissolved in the solvent and cooled in the trap were analyzed by GC-FID equipped with a UA-DX30capillary column.3.Results and discussion3.1.Characterization of Al 2O 3supportsFirst,Al 2O 3supports,which were prepared by the calcination of boehmite and gibbsite under different conditions,were char-acterized by XRD to conﬁrm the crystal phase of Al 2O 3(Fig.1).It is generally accepted that Al 2O 3precursors such as boehmite and gibbsite are transformed into several metastable Al 2O 3phases with increasing the calcination temperature before the thermo-dynamically stable ␣-Al 2O 3formed ﬁnally [39–42].Boehmite is transformed into ␣-Al 2O 3via ␥-,␦-and ␪-Al 2O 3.Two kinds of metastable Al 2O 3,␹-and ␬-Al 2O 3are obtained by the calcination of gibbsite before the formation of ␣-Al 2O 3.Phase transition temper-ature of Al 2O 3generally varies with the preparation method and the physicochemical properties of Al 2O 3precursors.In the present study,the calcination of boehmite led to the formation of ␥-Al 2O 3at 600–800◦C,␦-Al 2O 3at 900◦C and ␪-Al 2O 3at 1000–1050◦C,respec-tively (Fig.1(A)and Table 1).Gibbsite was transformed into ␹-Al 2O 3at 600–800◦C and ␬-Al 2O 3at 850–1000◦C,respectively (Fig.1(B)and Table 1).Al-S was composed of ␥-Al 2O 3.Next,Al 2O 3supports were characterized by N 2adsorption.Table 1shows BET speciﬁc surface area,average pore size and pore volume of various Al 2O 3supports.BET speciﬁc surface area,average pore size and pore volume of the Al-B supports were 68–200m 2g −1,12–25nm and 0.42–0.60cm 3g −1,respectively.As the calcination temperature of boehmite increased,BET speciﬁc surface area and pore volume decreased but average pore size increased.This is reasonable because the sintering of Al 2O 3par-ticles is promoted with increasing the calcination temperature.Onthe other hand,BET speciﬁc surface area,average pore size and pore volume of the Al-G supports were 21–164m 2g −1,6–48nm and ca.0.26cm 3g −1,respectively.As with the Al-B supports,BET speciﬁc surface area of the Al-G supports decreased but average pore size increased with an increase of the calcination tempera-ture of gibbsite.However,pore volume of the Al-G supports did not vary with the calcination temperature of paring with the samples having the same surface area,average pore size and pore volume of the Al-B supports were larger than those of the Al-G supports (Fig.2).The pore parameters of the Al-S support were comparable with those of the Al-G supports having the same surface area,as shown in Table 1and Fig.2.Pore size distributions of Al 2O 3supports were shown in Fig.3(white circle).As the calcination temperature of Al 2O 3pre-cursor increased,pore size of the Al-B and Al-G supports became larger and pore size distribution became broader.Pore size distri-butions of the Al-G supports were narrower than those of the Al-B supports,when the calcination temperature of Al 2O 3precursor was lower than 900◦C.Pore size distribution of the Al-S support was similar to that of the Al-G(850,10)and Al-G(900,3)supports.As mentioned above,we successfully prepared various Al 2O 3supports having different crystal phase and pore structures by calcination of boehmite and gibbsite under various conditions.Thus,Co/Al 2O 3catalysts were prepared using these Al 2O 3supports.Results of structural analysis and reaction tests for the prepared Co/Al 2O 3catalysts will be introduced in the following sections.3.2.Characterization of Co/Al 2O 3catalystsCo/Al 2O 3catalysts,which were prepared by an impregnation,drying and calcination,were characterized by N 2adsorption,XRD,H 2-TPR,H 2-chemisorption and TEM.Results of N 2adsorption were shown in Table 2.BET speciﬁc surface area,average pore size and pore volume of the Co/Al-B catalysts were 56–150m 2g −1,Cu K α 2θ / degreeI n t e n s i t y / c p s(B)Cu K α 2θ / degreeI n t e n s i t y / c p s(A)Fig.1.XRD patterns of various Al 2O 3supports:(A)Al-B,(B)Al-G and Al-S (♦:␥-Al 2O 3, :␦-Al 2O 3, :␪-Al 2O 3, :␹-Al 2O 3,᭹:␬-Al 2O 3).K.Shimura et al./Journal of Molecular Catalysis A:Chemical 394(2014)22–3225Table 1Physicochemical properties of Al 2O 3supports.EntrySupportCrystal phase of Al 2O 3aBET speciﬁc surface area b (m 2g −1)Average pore size b (nm)Pore volume b (cm 3g −1)1Al-B(600,3)␥20012.00.602Al-B(700,3)␥17813.20.593Al-B(800,3)␥15415.20.584Al-B(800,10)␥14516.10.595Al-B(900,3)␦12817.50.566Al-B(900,10)␦10719.20.527Al-B(1000,3)␪9122.90.528Al-B(1000,10)␪8424.30.519Al-B(1050,10)␪6824.70.4210Al-G(600,3)␹164 6.30.2611Al-G(700,3)␹1367.90.2712Al-G(800,10)␹1009.90.2513Al-G(850,10)␬8212.80.2614Al-G(900,3)␬7813.40.2615Al-G(900,10)␬5220.40.2616Al-G(950,10)␬3134.60.2717Al-G(1000,10)␬2147.80.2618Al-S␥9012.50.28a Determined by XRD.bDetermined by N 2adsorption.BET specific surface area / m 2 g -1P o r e v o l u m e / c m 3 g -1(B)(A)A v e r a g e p o r e s i z e /n mBET specific surface area / m 2 g -1Fig.2.Physicochemical properties of Al 2O 3supports.(A)Average pore size and (B)pore volume of Al 2O 3supports are plotted against the BET speciﬁc surface area.11–21nm and 0.29–0.41cm 3g −1,respectively.BET speciﬁc surfacearea,average pore size and pore volume of the Co/Al-G catalysts were 15–114m 2g −1,6–40nm and ca.0.17cm 3g −1,respectively.The values of these three parameters for Co/Al 2O 3catalysts were smaller than the values for the bare Al 2O 3supports,since pores of Al 2O 3support were blocked by deposited Co particles.However,the pore parameters of Co/Al 2O 3catalysts basically depended on the pore structure of bare Al 2O 3supports.Pore size distributions of Co/Al 2O 3catalysts were shown in Fig.3(black circle).As with the bare Al 2O 3supports,pore size of the Co/Al-B and Co/Al-G catalysts became larger and pore size distribu-tion became broader with increasing the calcination temperature of Al 2O 3precursor.Deposition of Co particles on the Al 2O 3sup-ports by the impregnation,drying and calcination did not change the pore size distribution but merely reduced the nitrogen uptake,as reported by other research groups [19,20,25].Co/Al 2O 3catalysts before hydrogen reduction pretreatments were analyzed by XRD (data not shown).From XRD patterns of all Co/Al 2O 3catalysts,only peaks assigned to Al 2O 3and Co 3O 4were observed.Peaks of other Co compounds such as CoO and Co alumi-nate were not observed.Particle size of Co metal on all Co/Al 2O 3catalysts was estimated from the diffraction line at 36.9◦using the Scherrer equation and Eq.(1),and results were listed in Table 2.Co particle sizes of the Co/Al-B,Co/Al-G and Co/Al-S catalysts were 11–16nm,16–20nm and 13nm,respectively.Co particle size of all Co/Al-B catalysts was smaller than the average pore size of Al 2O 3support.This suggests that at least parts of Co particles on the Co/Al-B catalysts would exist inside the pores of Al 2O 3support.In contrast,Co particle sizes of the Co/Al-G catalysts calcined at 900◦C and lower temperatures were clearly larger than the average pore sizes of Al 2O 3support.This indicates that many Co particles on these Co/Al-G catalysts would exist on the outer surface of Al 2O 3support.From these results,we speculate that Co particles having relatively uniform sizes would form on the Co/Al-B catalysts due to the restriction of Co particles inside the pores.However,the size distribution of Co particles on the Co/Al-G catalysts would be rather heterogeneous,since many Co particles exist on the open surface.As the calcination temperature of Al 2O 3precursors increased,Co particle size of the Co/Al-B catalysts increased.In contrast,Co par-ticle size of the Co/Al-G catalysts decreased with an increase of calcination temperature until 900◦C before it became constant.The different tendency of Co particle size with respect to the calcination temperature of Al 2O 3precursor would be attributed to the differ-ences in the place of Co particles deposited on the Al 2O 3support.Over the Co/Al-B catalysts,Co particles would mainly exist inside the pores of Al 2O 3support.Therefore,Co particle size increased with increasing the calcination temperature of boehmite,since the pore size also increased with the calcination temperature.On the other hand,over the Co/Al-G catalysts,many Co particles would exist on the outer surface due to the very small pore size,when the26K.Shimura et al./Journal of Molecular Catalysis A:Chemical 394(2014)22–32Pore size / nmP o r e v o l u m e / a .u .(A)Pore size / nmP o r e v o l u m e / a .u .(B)Fig.3.Pore size distribution of Al 2O 3supports (white circle)and Co/Al 2O 3catalysts (black circle):(A)Co/Al-B;(B)Co/Al-G and Co/Al-S.Table 2Physicochemical properties of Co/Al 2O 3catalysts.EntryCatalystBET speciﬁc surface area a (m 2g −1)Average pore size a (nm)Pore volume a (cm 3g −1)Particle size of Co metal b (nm)1Co/Al-B(600,3)15010.80.4110.82Co/Al-B(700,3)13312.00.4010.83Co/Al-B(800,3)11213.10.3711.24Co/Al-B(800,10)11014.20.3912.45Co/Al-B(900,3)8615.90.3412.16Co/Al-B(900,10)8617.20.3713.27Co/Al-B(1000,3)6519.50.3214.18Co/Al-B(1000,10)6621.10.3514.69Co/Al-B(1050,10)5620.90.2915.610Co/Al-G(600,3)114 6.10.1720.211Co/Al-G(700,3)947.20.1718.412Co/Al-G(800,10)758.90.1717.813Co/Al-G(850,10)5911.30.1717.714Co/Al-G(900,3)5512.00.1616.915Co/Al-G(900,10)3617.40.1616.216Co/Al-G(950,10)2528.60.1816.717Co/Al-G(1000,10)1540.20.1516.018Co/Al-S7010.90.1912.6a Determined by N 2adsorption.bDetermined by XRD.calcination temperature of gibbsite was lower than 900◦C.Thus,the size of Co particles would not be sufﬁciently controlled,and large Co particles as well as small ones would form on the outer surface,resulting in an increase of average Co particle size.We also speculate that increase in the calcination temperature of gibbsite enlarges the pore size and increases the number of Co particles formed inside the pores.Therefore,the average Co particle size became small,since the size of Co particles would be controlled by pores to some extent.Fig.4shows the H 2-TPR proﬁles of various Co/Al 2O 3catalysts.It is generally accepted that the peak observed at 300–400◦C corre-sponds to the reduction of Co 3O 4to CoO and peaks at 400–600◦C correspond to the reduction of CoO to Co metal [3].Similarly,peaks observed at 600◦C and higher temperatures should originate from the reduction of barely reducible Co species such as cobaltaluminate.H 2-TPR proﬁles of the Co/Al-B catalysts were relatively similar to each other and did not depend on the calcination temper-ature of boehmite.On the other hand,we observed from the spectra of Co/Al-G catalysts that peaks at 600–800◦C became smaller with increasing the calcination temperature of gibbsite.This shows that the reducibility of Co particles on the Co/Al-G catalysts increases with increasing the calcination temperature of gibbsite.Increase of Co reducibility was especially high,when the calcination temper-ature of gibbsite was higher than 900◦C.Reduction degree of Co (D red ),corrected dispersion of Co metal (D corr )and surface area of Co metal (SA)were measured by H 2-TPR and H 2chemisorption,and results were listed in Table 3.D red of the Co/Al-B,Co/Al-G and Co/Al-S catalysts was 54–64%,60–97%and 62%,respectively.D red of the Co/Al-B catalysts did not largely vary with the calcination temperature of boehmite.D red of the Co/Al-GK.Shimura et al./Journal of Molecular Catalysis A:Chemical 394(2014)22–3227100 20030 040 0 50060 0 70080 090 0Al-G(600, 3 ) H 2 c o n s u m p t i o n / a .u .Reduction temperature / ˚CAl-G(700, 3)Al-G(800, 10) Al-G(900, 3 ) Al-G(850, 10) Al-G(950, 10) Al-G(900, 1 0) (B)Al-G(1000, 1 0) Al-S10020 030 040 0 50060 070 080 0 900Reduction temperature / ˚CH 2 c o n s u m p t i o n / a .u .Al-B(600, 3) Al-B(700, 3) Al-B(800, 3)Al-B(900, 3) Al-B(800,10 ) Al-B(1000, 3) Al-B(900, 10 ) (A)Al-B(1000, 10)Al-B(1050,10) Fig.4.H 2-TPR proﬁles of various Co/Al 2O 3catalysts:(A)Co/Al-B;(B)Co/Al-G and Co/Al-S.Table 3Structural analysis of various Co/Al 2O 3catalysts.EntryCatalystD red a(%)D corr b(%)SA c (m 2g −1)1Co/Al-B(600,3)540.480.402Co/Al-B(700,3)570.530.473Co/Al-B(800,3)570.490.424Co/Al-B(800,10)620.640.615Co/Al-B(900,3)550.450.386Co/Al-B(900,10)590.640.587Co/Al-B(1000,3)610.880.828Co/Al-B(1000,10)64 1.21 1.189Co/Al-B(1050,10)63 1.03 1.0010Co/Al-G(600,3)670.960.9911Co/Al-G(700,3)61 1.20 1.1212Co/Al-G(800,10)62 1.05 1.0113Co/Al-G(850,10)62 1.16 1.0914Co/Al-G(900,3)60 1.040.9615Co/Al-G(900,10)73 1.30 1.4516Co/Al-G(950,10)84 1.11 1.4217Co/Al-G(1000,10)970.83 1.2518Co/Al-S621.241.19a Reduction degree of Co.b Corrected dispersion of Co metal.cSurface area of Co metal.catalysts was constant,when the calcination temperature of gibb-site was lower than 900◦C.However,further increase of calcination temperature drastically increased D red .D corr of the Co/Al-B,Co/Al-G and Co/Al-S catalysts was 0.45–1.21%,0.83–1.30%and 1.24%,respectively.D corr of the Co/Al-B catalysts was almost constant,when the calcination temperature of boehmite was lower than 900◦C.However,D corr of the Co/Al-B catalysts calcined at 1000◦and 1050◦C was clearly higher than D corr of other catalysts.D corr of the Co/Al-G catalysts did not largely vary with the calcination tem-perature,as compared with the Co/Al-B catalysts.However,D corr of the Co/Al-G(1000,10)catalyst was a little lower than D corr ofthe other Co/Al-G catalysts probably due to the very small sur-face area of the Al-G(1000,10)support.SA of the Co/Al-B,Co/Al-G and Co/Al-S catalysts was 0.38–1.18m 2g −1,0.96–1.45m 2g −1and 1.19m 2g −1,respectively and showed almost the same tendency as D corr with respect to the calcination temperature of Al 2O 3precur-sors.D red ,D corr and SA were also plotted against BET speciﬁc surface area of Al 2O 3supports (Fig.5).When BET speciﬁc surface area of Al 2O 3support was higher than 70m 2g −1,D red was almost constant around 60%and did not depend on the kinds of Al 2O 3precur-sor and the crystal phase of Al 2O 3support (Fig.5(A)).However,when the surface area was lower than 70m 2g −1,D red drastically increased with decreasing the surface area.Increase in the D red with decreasing the surface area (i.e.increasing the pore size)of Al 2O 3supports was reported by several other research groups [19,20,28].They suggest that larger Co particles tend to be formed on Al 2O 3supports having lower surface area (rger pore size)and the weak interaction between large Co particles and Al 2O 3support promotes the reduction of Co particles.Another reason is that the diffusion of water molecules formed during H 2reduction pretreat-ment would be inﬂuenced by the pore size of Al 2O 3support.Since the residence time of water is shorter over the Al 2O 3supports hav-ing larger pores,inﬂuence of the produced water on the reoxidation of Co metal particles is also smaller over the Al 2O 3supports hav-ing larger pores,resulting in an enhancement of Co reducibility.D corr and SA of the Co/Al-B catalysts showed a similar tendency with those of the Co/Al-G catalysts with respect to the surface area of Al 2O 3support (Fig.5(B)and (C)).As the surface area of Al 2O 3support decreased,D corr and SA were ﬁrst constant,then increased and ﬁnally decreased.The highest D corr and SA were obtained over the Co/Al-B(1000,10)and Co/Al-G(900,10)catalysts,which were prepared from Al 2O 3supports having moderate surface area.The reason why D corr and SA depended on the surface area of Al 2O 3support was explained as follows:over the Al 2O 3supports having。

英文文献-溶胶-凝胶法制备LiFePO4改进其电化学性能

Electrochimica Acta 92 (2013) 248–256Contents lists available at SciVerse ScienceDirectElectrochimicaActaj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e l e c t a c taGel-combustion synthesis of LiFePO 4/C composite with improved capacity retention in aerated aqueous electrolyte solutionMilica Vujkovi´c a ,Ivana Stojkovi´c a ,Nikola Cvjeti´canin a ,Slavko Mentus a ,b ,∗,1a University of Belgrade,Faculty of Physical Chemistry,P.O.Box 137,Studentski trg 12-16,11158Belgrade,Serbia bThe Serbian Academy of Sciences and Arts,Kenz Mihajlova 35,11158Belgrade,Serbiaa r t i c l ei n f oArticle history:Received 2October 2012Received in revised form 3January 2013Accepted 5January 2013Available online 11 January 2013Keywords:Aqueous rechargeable Li-ion battery Galvanostatic cycling Gel-combustion Olivine LiFePO 4LiFePeO 4/C compositea b s t r a c tThe LiFePO 4/C composite containing 13.4wt.%of carbon was synthesized by combustion of a metal salt–(glycine +malonic acid)gel,followed by an isothermal heat-treatment of combustion product at 750◦C in reducing atmosphere.By a brief test in 1M LiClO 4–propylene carbonate solution at a rate of C/10,the discharge capacity was proven to be equal to the theoretical one.In aqueous LiNO 3solu-tion equilibrated with air,at a rate C/3,initial discharge capacity of 106mAh g −1was measured,being among the highest ones observed for various Li-ion intercalation materials in aqueous solutions.In addition,signiﬁcant prolongation of cycle life was achieved,illustrated by the fact that upon 120charg-ing/discharging cycles at various rates,the capacity remained as high as 80%of initial value.The chemical diffusion coefﬁcient of lithium in this composite was measured by cyclic voltammetry.The obtained val-ues were compared to the existing literature data,and the reasons of high scatter of reported values were considered.© 2013 Elsevier Ltd. All rights reserved.1.IntroductionThanks to its high theoretical Coulombic capacity (170mAh g −1)and environmental friendliness,LiFePO 4olivine became a desir-able cathodic material of Li-ion batteries [1,2],competitive to other commercially used cathodic materials (LiMnO 4,LiCoO 2).As evidenced in non-aqueous electrolyte solutions,a small vol-ume change (6.81%)that accompanies the phase transition LiFePO 4 FePO 4enables Li +ion insertion/deinsertion reactions to be quite reversible [1–3].The problem of low rate capability,caused by low electronic conductivity [4,5],was shown to be solv-able to some extent by reduction of mean particle size [6].Further improvements in both conductivity and electrochemical perform-ances were achieved by forming composite LiFePO 4/C,where in situ produced carbon served as an electronically conducting con-stituent [5,7–27].Ordinarily,both in situ formed carbon and carbon black additive,became unavoidable constituent of the LiFePO 4-based electrode materials [28–37].Zhao et al.[27]reported that Fe 2P may arise as an undesirable product during the synthesis of LiFePO 4/C composite under reducing conditions,however,other authors found later that this compound may contribute positively∗Corresponding author at:University of Belgrade,Faculty of Physical Chemistry,P.O.Box 137,Studentski trg 12-16,11158Belgrade,Serbia.Tel.:+381112187133;fax:+381112187133.E-mail address:slavko@ffh.bg.ac.rs (S.Mentus).1ISE member.to the electronic conductivity and improve the electrochemical per-formance of the composite [28–30].Severe improvement in rate capability and capacity retention was achieved by partial replace-ment of iron by metals supervalent relative to lithium [31–37].Thus one may conclude that the main aspects of practical applica-bility of LiFePO 4in Li-ion batteries with organic electrolytes were successively resolved.After the pioneering studies by Li and Dahn [38,39],recharge-able Li-ion batteries with aqueous electrolytes (ARLB)attracted considerable attention [40–50].The ﬁrst versions of ARLB’s,suf-fered of very low Coulombic utilization and signiﬁcantly more pronounced capacity fade relative to the batteries with organic electrolyte,regardless on the type of electrode materials [43].For the ﬁrst time,LiFePO 4was considered as a cathode material in ARLB’s by Manickam et al.in 2006[44].He et al.[46],in an aqueous 0.5M Li 2SO 4solution,found that LiFePO 4displayed both a surprisingly high initial capacity of 140mAh g −1at a rate 1C and recognizable voltage plateau at a rate as high as 20C,which was superior relative to the other electrode materials in ARLB’s.Recently,the same authors reported a high capacity decay in aer-ated electrolyte solution,amounting to 37%after only 10cycles [48].In the same study,they demonstrated qualitatively by a brief cyclovoltammetric test,that a carbon layer deposited from a vapor phase over LiFePO 4particles,suppressed the capacity fade [48].Inspired by the recent discoveries about excellent rate capa-bility [46]but short cycle life [48]of LiFePO 4in aerated aqueous solution,we attempted to prolong the cycle life by means of protecting carbon layer over the LiFePO 4particles.Therefore we0013-4686/$–see front matter © 2013 Elsevier Ltd. All rights reserved./10.1016/j.electacta.2013.01.030M.Vujkovi´c et al./Electrochimica Acta92 (2013) 248–256249synthesized LiFePO4/C composite by a fast and simple glycine-nitrate gel-combustion technique.This method,although simpler than a classic solid state reaction method combined with ball milling[44,48],was rarely used for LiFePO4synthesis[19,27].It yielded a porous,foamy LiFePO4/C composite,easily accessible to the electrolyte.Upon the fair charging/discharging performance was conﬁrmed by a brief test in organic electrolyte,we examined in detail the electrochemical behavior of this material in aqueous electrolyte,by cyclic voltammetry,complex impedance and cyclic galvanostatic charging/discharging methods.In comparison to pure LiFePO4studied in Ref.[48],this composite displayed markedly longer cycle life in aerated aqueous solutions.The chemical dif-fusion coefﬁcient of lithium was also determined,and the reasons of its remarkable scatter in the existing literature were considered.2.ExperimentalThe LiFePO4/C composite was synthesized using lithium nitrate, ammonium dihydrogen phosphate(Merck)and iron(II)oxalate dihydrate(synthesized according to the procedure described else-where[51])as raw materials.Our group acquired the experience in this synthesis technique on the examples of spinels LiMn2O4 [52]and LiCr0.15Mn1.85O4[53],where glycine served as both fuel and complexing/gelling agent to the metal ions.A stoichiometric amount of each material was dissolved in deionized water and mixed at80◦C using a magnetic stirrer.Then,ﬁrst glycine was added into the reaction mixture to provide the mole ratio of glycine: nitrate of2:1,and additionally,malonic acid(Merck)was added in an amount of60wt.%of the expected mass of LiFePO4.The role of malonic acid was to decelerate combustion and provide con-trollable excess of carbon[14].After removing majority of water by evaporation,the gelled precursor was heated to initiate the auto-combustion,resulting in aﬂocculent product.The combustion product was heated in a quartz tube furnaceﬁrst at400◦C for3h in Ar stream,and then at750◦C for6h,under a stream of5vol.%H2in Ar.This treatment consolidated the olivine structure and enabled to complete the carbonization of residual organic matter.The VO2powder prepared by hydrothermal method was used as an active component of the counter electrode in the galvanostatic experiments in aqueous electrolyte solution.The details of the syn-thesis and electrochemical behavior of VO2are described elsewhere [54,55].The considerable stoichiometric excess of VO2was used,to provide that the LiFePO4/C composite only presents the main resis-tive element,i.e.,determines the behavior of the assembled cell on the whole.The XRD experiment was performed using Philips1050diffrac-tometer.The Cu K␣1,2radiation in15–70◦2Ârange,with0.05◦C step and2s exposition time was used.The carbon content in the composite was determined by its com-bustion in theﬂowing air atmosphere,by means of thermobalance TA SDT Model2090,at a heating rate of10◦C min−1.The morphology of the synthesized compounds was observed using the scanning electron microscope JSM-6610LV.For electrochemical investigations,the working electrode was made from LiFePO4/C composite(75%),carbon black-Vulcan XC72 (Cabot Corp.)(20%),poly(vinylideneﬂuoride)(PVDF)binder(5%) and a N-methyl-2-pyrrolidone solvent.The resulting suspension was homogenized in an ultrasonic bath and deposited on electron-ically conducting support.The electrode was dried at120◦C for 4h.Somewhat modiﬁed weight ratio,85:10:5,and the same drying procedure,were used to prepare VO2electrode.The non-aqueous electrolyte was1M LiClO4(Lithium Corpo-ration of America)dissolved in propylene carbonate(PC)(Fluka). Before than dissolved,LiClO4was dried over night at140◦C under vacuum.The aqueous electrolyte solution was saturated LiNO3solution.The cyclic voltammetry and complex impedance experiments were carried out only for aqueous electrolyte solutions,by means of the device Gamry PCI4/300Potentiostat/Galvanostat.The three electrode cell consisted of a working electrode,a wide platinum foil as a counter electrode,and a saturated calomel electrode(SCE) as a reference one.The experiments were carried out in air atmo-sphere.The impedance was measured in open-circuit conditions, at various stages of charging and discharging,within the frequency range10−2−105Hz,with7points per decade.Galvanostatic charging/discharging experiments were carried out in a two-electrode arrangement,by means of the battery testing device Arbin BT-2042,with two-terminal connectors only.In the galvanostatic tests in non-aqueous solution,working electrode was a2×2cm2platinum foil carrying2.3mg of compos-ite electrode material(1.5mg of olivine),while counter electrode was a2×2cm2lithium foil.The cell was assembled in an argon-ﬁlled glove box and cycled galvanostatically within a voltage range 2.1–4.2V.The galvanostatic tests in the aqueous electrolyte solution were carried out in a two-electrode arrangement,involving3mg of cathodic material,as a working electrode,and VO2in a multi-ple stoichiometric excess,as a counter electrode.According to its reversible potential of lithiation/delithiation reaction[55],VO2per-formed as an anode in this cell.The4cm2stainless steel plates were used as the current collectors for both positive and negative electrode.The cell was assembled in room atmosphere,and cycled within the voltage window between0.01and1.4V.3.Result and discussion3.1.The XRD,SEM and TG analysis of the LiFePO4/C compositeFig.1shows the XRD patterns of the composite LiFePO4/C pre-pared according to the procedure described in the Experimental Section.As visible,the diffractogram agrees completely with the one of pure LiFePO4olivine,found in the JCPDS card No.725-19. The narrow diffraction lines indicate complete crystallization and relatively large particle dimensions.On the basis of absence of diffraction lines of carbon,we may conclude that the carbonized product was amorphous one.Fig.2shows the SEM images of the LiFePO4/C composite at two different magniﬁcations.Theﬂaky agglomerates,Fig.2left,with apparently smooth surface and low tap density,are due to a partial liquefaction and evolution of gas bubbles during gel-combustion procedure.These agglomerates consist of small LiFePO4/CFig.1.XRD patterns of LiFePO4/C composite in comparison to standard crystallo-graphic data.250M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256Fig.2.SEM images of LiFePO 4/C composite at two different magniﬁcation,20000×and 100000×.composite particles visible better at higher magniﬁcation,Fig.2,ly at the magniﬁcation of 100,000×,one may see that the size of majority of composite particles was in the range 50–100nm.The mean particle diameter,2r,as per SEM microphotograph amounted to 75nm.This analysis evidences that the gel-combustion method may provide nanodisprsed particles,desirable from the point of view of rate capability.For instance,Fey et al.[16]demonstrated that particle size reduction from 476to 205nm improved the rate capa-bility of LiFePO 4/C composite in organic electrolyte,illustrated by the increase of discharge capacity from 80mAh g −1to 140mAh g −1at discharging rate 1C.Also,carbon matrix prevented particles from agglomeration providing narrow size distribution,contrary to often used solid state reaction method of synthesis,when sintering of ini-tially nanometer sized particles caused the appearance of micron sized agglomerates [22].The SEM microphotograph (Fig.2)alone did not permit to rec-ognize carbon constituent of the LiFePO 4/C composite.However,carbonized product was evidenced,and its content measured,by means of thermogravimetry,as described elsewhere [9].The dia-gram of simultaneous thermogravimetry and differential thermal analysis (TG/DTA)of the LiFePO 4/C composite performed in air is presented in Fig.3.The process of moisture release,causing a slight mass loss of 1%,terminated at 150◦C.In the temperature range 350–500◦C carbon combustion took place,visible as a drop of the TG curve and an accompanying exothermic peak of the DTA curve.However,the early stage of olivine oxidation merged to some extent with the late stage of carbon combustion,and therefore,the minimum of the TG curve,appearing at nearly 500◦C,was not so low as to enable to read directly the carbon content.Fortunately,as proven by XRD analysis,the oxidation of LiFePO 4at tempera-ture exceeding 600◦C,yielded only Li 3Fe 2(PO 4)3and Fe 2O 3,whatFig.3.TGA/DTA curve of LiFePO 4/C under air ﬂow at heating rate of 10C min−1.corresponded to the relative gain in mass of exactly 5.07%[9].Therefore,the weight percentage of carbonaceous fraction in the LiFePO 4/C composite was determined as equal to the difference between the TG plateaus at temperatures 300and 650◦C,aug-mented for 5.07%.According to this calculation the carbon fraction amounted to 13.4wt.%,and by means of this value,the electro-chemical parameters discussed in the next sections were correlated to pure LiFePO 4.Speciﬁc surface area of LiFePO 4,required for the measurement of diffusion constant,was determined from SEM image (Fig.2).Assuming a spherical particle shape and accepting mean particle radius r =37.5nm,the speciﬁc surface area was estimated on the basis of equation [17,22,45,46]:S =3rd(1)where the bulk density d =3.6g cm −3was used .This calculation resulted in the value S =22.2m 2g −1.In this calculation the contri-bution of carbon to the mean particle radius was ignored,however the error introduced in such way is more acceptable than the error which may arise if standard BET method were applied to the com-posite with signiﬁcant carbon ly,due to a usually very developed surface area of carbon,the measured speciﬁc sur-face may exceed many times the actual surface area of LiFePO 4.3.2.Electrochemical measurements3.2.1.Non-aqueous electrolyte solutionIn order to compare the behavior of the synthesized LiFePO 4/C composite to the existing literature data,available predominantly for non-aqueous solutions,a brief test was performed in non-aqueous 1M LiClO 4+propylene carbonate solution by galvano-static experiments only.The results for the rates C/10,C/3and C,within the voltage limits 2.1–4.2V,were presented in Fig.4.The polarizability of the lithium electrode was estimated on the basis of the study by Churikov [56–67],who measured the current–voltage curves of pure lithium electrode in LiClO 4/propylene carbon-ate solutions at various temperatures.To the highest rate of 1C =170mA g −1in nonaqueous electrolyte,the corresponding cur-rent amounted to 0.25mA,which was equal to the current density of 0.064mA cm −2through the Li counter electrode.According to Fig.2in Ref.[67],for room temperature,the corresponding over-voltage amounted to only 6mV.Since lithium electrode is thus practically non-polarizable in this system,the voltages presented on the ordinate of the left diagram are the potentials of the olivine electrode expressed versus Li/Li +reference electrode.The clear charge and discharge plateaus at about 3.49V and 3.40V,respec-tively,correspond to the LiFePO 4 FePO 4phase equilibria [5].At discharging rate of C/10,the initial discharge capacity,within the limits of experimental error,was close to a full theoreticalM.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256251Fig.4.The initial charge/discharge curves (a)and cyclic performance (b)of LiFePO 4/C composite in 1M LiClO 4+PC at different rates within a common cut-off voltage of2.1–4.2V.Fig.5.Charge/discharge proﬁle and corresponding cyclic behavior of LiFePO 4/C in 1M LiClO 4+PC at the rate of 1C.capacity of LiFePO 4(170mAh g −1).This value is higher than that for LiFePO 4/C composite obtained by glycine [19],malonic acid [14]and adipic acid/ball milling [15]assisted methods.As usual,the discharge capacity decreased with increasing discharging rate (Fig.4b),and amounted to 127mAh g −1at C/3,and 109mAh g −1at 1C.For practical application of Li-ion batteries,a satisfactory rate capability and long cycle life are of primary importance.The charge/discharge proﬁles and dependence of capacity on the cycle number at the rate 1C are presented in Fig.5.The capacity was almost independent on the number of cycles,similarly to theearlier reports by Fey et al.[37–39].For comparison,Kalaiselvi et al.[19],by a glycine assisted gel-combustion procedure,with an additional amount (2wt.%)of carbon black,produced a similar nanoporous LiFePO 4/C composite displaying somewhat poorer per-formance,i.e.,smaller discharge capacity of 160mAh g −1at smaller discharging rate of C/20.On the other hand,better rate capability of LiFePO 4/C com-posite,containing only 1.1–1.8wt.%of carbon,in a non-aqueous solution,was reported by Liu et al.[21].For instance they mea-sured 160mAh g −1at the rate 1C,and 110at even 30C [21].This may be due to a thinner carbon layer around the LiFePO 4olivine particles.However the advantage of here applied thicker carbon layer exposed itself in aqueous electrolyte solutions,as described in the next section.3.2.2.Aqueous electrolyte solution3.2.2.1.Cyclic voltammetry.By the cyclic voltammetry method (CV)the electrochemical behavior of LiFePO 4/C composite in satu-rated aqueous LiNO 3solution was preliminary tested in the voltage range 0.4–1V versus SCE.The cyclic voltammograms are pre-sented in Fig.6.The highest scan rate of 100mV s −1,tolerated by this material,was much higher than the ones (0.01–5mV s −1)used in previous studies in both organic [13,24,25]and aqueous electrolyte solutions [47,48].Since one deals here with the thin layer solid redox electrode,limited in both charge consumption and diffusion length,the voltammogram is more complicated for interpretation comparing with the classic case of electroactive species in a liquid solution.A sharp,almost linear rise of current upon achieving reversible potential,with overlapped rising parts at various scan rates,similar to ones reported elsewhere [21,25],resembles closely the voltammogram of anodic dissolution ofaFig.6.Cyclic voltammograms of LiFePO 4/C in saturated LiNO 3aqueous electrolyte with a scan rate of 1mV s −1(left)and at various scan rates in the range 1–100mV s −1.252M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256Fig.7.Anodic and cathodic peak current versus square root of scan rate forLiFePO 4/C composite in aqueous LiNO 3electrolyte solution.thin metal layer [56],which proceeds under constant reactant activity.Since the solid/solid phase transitions LiFePO 4 FePO 4accompanies the redox processes in this system [5,8,57,58],the positive scan of the voltammograms depict the phase transition of LiFePO 4to FePO 4,while the negative scan depicts the phase transi-tion FePO 4to LiFePO 4.As shown by Srinivasan et al.[5],LiFePO 4may be exhausted by Li not more than 5mol.%before to trans-form into FePO 4,while FePO 4may consume no more than 5%Li before to transform into LiFePO 4,i.e.cyclic voltammetry exper-iments proceeds under condition of almost constant activity of the electroactive species.Although these aspects of the Li inser-tion/deinsertion process do not ﬁt the processes at metal/liquid electrolyte boundary implied by Randles–Sevcik equation:i p =0.4463F RT1/2C v 1/2AD 1/2(2)this equation was frequently used to estimate apparent diffusion coefﬁcient in Li insertion processes [5,17,21,46,59].To obtain peak current,i p ,in amperes,the concentration of lithium,C =C Li ,should be in mol cm −3,the real surface area exposed to the electrolyte in cm 2,chemical diffusion coefﬁcient of lithium through the solid phase,D =D Li ,in cm 2s −1,and sweep rate,v ,in V s −1.The Eq.(2)pre-dicts the dependence of the peak height on the square root of sweep rate to be linear,as found often in Li-ion intercalation processes [17,21,25,59,60].This condition is fulﬁlled in this case too,as shown in Fig.7.The average value of C Li may be estimated as a reciprocal value of molar volume of LiFePO 4(V M =44.11cm 3mol −1),hence C Li =2.27×10−2mol cm −3.The determination of the actual surface area of olivine is a more difﬁcult task,due to the presence of carbon in the LiFePO 4/C ly,classical BET method of sur-face area measurement may lead to a signiﬁcantly overestimated value,since carbon surface may be very developed and participate predominantly in the measured value [15].Thus the authors in this ﬁeld usually calculated speciﬁc surface area by means of Eq.(1),using mean particle radius determined by means of electron microscopy [17,22,45,46].Using S =22.2m 2g −1determined by means of Eq.(1),and an actual mass of the electroactive substance applied to the elec-trode surface (0.001305g),the actual electrode surface area was calculated to amount to A =290cm 2.This value introduced in Randles–Sevcik equation yielded D Li ∼0.8×10−14cm 2s −1.From the aspect of capacity retention,the insolubility of olivine in aqueous solutions is advantageous compared to the vanadia-based Li-ion intercalation materials,such as Li 1.2V 3O 8[61],LiV 3O 8[62]and V 2O 5[63],the solubility of which in LiNO 3solution was perceivable through the yellowish solutioncoloration.Fig.8.The Nyquist plots of LiFePO 4/C composite in aqueous LiNO 3solution at var-ious stages of delithiation;inset:enlarged high-frequency region.3.2.2.2.Impedance measurements.Figs.8and 9present the Nyquist plots of the LiFePO 4/C composite in aqueous LiNO 3solution at various open circuit potentials (OCV),during delithiation (anodic sweep,Fig.8)and during lithiation (cathodic sweep,Fig.9).The delithiated phase,observed at OCV =1V,as well as the lithi-ated phase,observed at OCV =0V,in the low-frequency region (f <100Hz)tend to behave like a capacitor,characteristic of a surface thin-layered redox material with reﬂective phase bound-ary conditions [64].At the OCV not too far from the reversible one (0.42V during delithiation,0.308V during lithiation),where both LiFePO 4and FePO 4phase may be present,within the whole 10−2–105Hz frequency range,the reaction behaves as a reversible one (i.e.shows the impedance of almost purely Warburg type).The insets in Figs.8and 9present the enlarged parts of the impedance diagram in the region of high frequencies,where one may observe a semicircle,the diameter of which corresponds theoretically to the charge transfer resistance.As visible,the change of open circuit potential between 0and 1V,in spite of the phase transition,does not cause signiﬁcant change in charge transfer resistance.The small charge transfer resistance obtained with the carbon participation of 13.4%,being less than 1 ,is the smallest one reported thus far for olivine based materials.This ﬁnding agrees with the trend found by Zhao et al.[27],that the charge transfer resistance scaleddownFig.9.The Nyquist plots of LiFePO 4/C composite in aqueous LiNO 3solution at var-ious stages of lithiation;inset:enlarged high-frequency region.M.Vujkovi´c et al./Electrochimica Acta 92 (2013) 248–256253Fig.10.The dependence Z Re vs.ω−1/2during lithiation at 0.308V (top)and delithi-ation at 0.42V (down)in the frequency range 72–2.68Hz.to 1000,400and 150 when the amount of in situ formed carbon in the LiFePO 4/C composite increased in the range 1,2.8and 4.8%.For OCV corresponding to the cathodic (0.42V)and anodic (0.308V)peak maxima,the Warburg constant W was calculated from the dependence [21]:Z Re =R e +R ct + W ω−1/2(3)In the frequency range 2.7–72Hz,almost purely Warburg impedance was found to hold (i.e.the slope of the Nyquist plot very close to 45degrees was found).At the potential of cathodic current maximum (0.42V),from Fig.10, W was determined to amount to 7.96 s −1/2.At the potential of anodic maxima,0.308V, W was determined to amount to 9.07 s −1/2.In the published literature,for the determination of diffusion coefﬁcient on the basis of impedance measurements,the following equation was often used [66,68,69]:D =0.5V M AF W ıE ıx2(4)where V M is molar volume of olivine,44.1cm 3, W is Warburg con-stant and ıE /ıx is the slope of the dependence of electrode potential on the molar fraction of Li (x )for given value of x .However,the potentials of CV maxima in the here studied case correspond to the x range of two-phase equilibrium,where for an accurate deter-mination of ıE /ıx a strong control of perturbed region of sample particles is required [69],and thus the determination of diffusion coefﬁcients was omitted.3.2.2.3.Galvanostatic measurements.The galvanostatic measure-ments of LiFePO 4/C in saturated LiNO 3aqueous solution were performed in a two-electrode arrangement using hydrother-mally synthesized VO 2[55]as the active material of thecounterFig.11.Capacity versus cycle number and charge/discharge proﬁles (inset)for thecell consisting of LiFePO 4/C composite as cathode,and VO 2in large excess as anode,in saturated LiNO 3aqueous electrolyte observed at rate C/3.electrode.Preliminary cyclovoltammetric tests of VO 2in saturated LiNO 3solution at the sweep rate 10mV s −1,evidenced excellent cyclability and stable capacity of about 160mAh g −1during at least 50cycles.The voltage applied to the two-electrode cell was cycled within the limits 0and 1.4V.Due to a signiﬁcant stoichiometric excess of VO 2over LiFePO 4/C composite (5:1)the actual voltage may be considered to be the potential versus reference VO 2/Li x VO 2electrode.Fig.11shows the dependence of the discharging Coulombic capacity of the LiFePO 4/C composite on the number of galvano-static cycles at discharging rate C/3,as well as (in the inset)the voltage vs.charging/discharging degree for 1st,2nd and 50th cycle.The charge/discharge curves do not change substantially in shape upon cycling,indicating stable capacity.For an aqueous solution,a surprisingly high initial discharge capacity of 106mAh g −1and low capacity fade of only 6%after 50charge/discharge cycles were evidenced.This behavior is admirable in comparison to other elec-trode materials in aqueous media reported in literature (LiTi 2(PO 4)3[42],LiV 3O 8[57]),and probably enabled by a higher thermody-namic stability of olivine structure [1].Fig.12presents the results of cyclic galvanostatic investigations of LiFePO 4/C composite in aqueous LiNO 3solution at various dis-charging rates.The charging/discharging rate was initially C/3for 80cycles and then was increased stepwise up to 3C.ThecapacityFig.12.Cyclic performance of LiFePO 4/C in saturated LiNO 3aqueous electrolyte at different charging/discharging rates.。

Surfactant-assisted synthesis and catalytic activity for SOx abatement of high-surface-area

CERAMICSINTERNATIONALAvailable online at Ceramics International 40(2014)5357–5363Surfactant-assisted synthesis and catalytic activity for SO x abatementof high-surface-area CuMgAlCe mixed oxidesHai-Tao Kang,Cong-Yun Zhang,Kai Lv,Shi-Ling Yuan nKey Lab of Colloid and Interface Chemistry,Shandong University,250100Jinan,China Received 21September 2013;received in revised form 23October 2013;accepted 24October 2013Available online 1November 2013AbstractCuMgAlCe mixed oxides were prepared by a modi ﬁed coprecipitation –calcination method using CTAB as surfactant template.All the precursors showed hydrotalcite-like layered structure and mixed oxides with mainly periclase phase were obtained after calcination.Catalytic activity for SO 2removal of mixed oxides was examined through adsorption –reduction cycles under the conditions similar to those of FCC units.The results showed that incorporation of both Ce and Cu could improve SO x oxidative chemisorption.CTAB/metal molar ratio during synthesis had a signi ﬁcant in ﬂuence on the structural properties of mixed oxides.Sample CuMgAlCe-0.1prepared by CTAB/metal molar ratio of 0.1had the highest speci ﬁc area 142.2m 2/g and also presented the best SO 2adsorption rate and capacity.This behavior is mainly due to its exposed more adsorption sites provided by high speci ﬁc surface area,facilitating SO 2diffusion and contact with active components.It still possessed excellent cyclic stability that is bene ﬁcial for industrial application.&2013Elsevier Ltd and Techna Group S.r.l.All rights reserved.Keywords:High surface area;SO 2removal;Mixed oxides;Hydrotalcite1.IntroductionFluid catalytic cracking (FCC)is one of the most important processes converting heavy oil to light oil,however it brings not only large economic bene ﬁt but also environmental problems,one of which is SO x pollution.After cracking reactions,it is necessary to burn off the coke deposited on the FCC catalyst in regenerator,and during this process burn-off of sulfur-containing coke will result in emission of SO x (about 80–90%SO 2and 10–20%SO 3)into atmosphere,directly leading to acid rain formation and ozone layer destruction [1–5].Along with the strengthening of people's eco-awareness and restriction of environmental laws,great attention has been focused on the ways to reduce SO x emissions in FCC units,mainly including ﬂue gas scrubbing,hydrodesulfurization and SO x transfer catalyst.Among them,the use of SO x transfer additives is regarded as the most practical method,requiring no additional investment except forthe material cost,which is determined by its working process in FCC units:(1)the oxidation of SO 2to SO 3under the FCC regenerator conditions;(2)the adsorption of SO 3to form sulfates;(3)the reduction of sulfates to release H 2S,which will be treated through Claus process [6,7].The whole process can be described as following reactions:SO 2ðg ÞþO 2ðg Þ-SO 3ðg Þðin regenerator Þð1ÞMO ðs ÞþSO 3ðg Þ-MSO 4ðs Þðin regenerator Þð2ÞMSO 4ðs Þþ4H 2ðg Þ-MO ðs Þþ3H 2O ðg ÞþH 2S ðg Þðin reactor Þð3ÞMany efforts have been devoted to design effective SO x transfer additives and MgAl mixed oxides derived from hydrotalcite-like compounds have been regarded as desirable materials for SO x removal in FCC units [8–12].The precur-sors,hydrotalcites,known as layered double hydroxides (LDH),are a sort of typical anionic layered materials.The structure are similar to that of brucite [Mg(OH)2],consisting of positively charged metal hydroxide layers and anions that/locate/ceramint0272-8842/$-see front matter &2013Elsevier Ltd and Techna Group S.r.l.All rights reserved./10.1016/j.ceramint.2013.10.116nCorresponding author.Tel:þ8653188365896.E-mail address:shilingyuan@ (S.-L.Yuan).occupy the interlayer spacing along with water molecules.Thechemical formula can be expressed as [M II 1Àx M III x (OH)2]x þ[(A n À)x /n Ám H 2O]x Àwhere M II and M III represent divalent and trivalent cations respectively,A n Àis an n -valent anion (often carbonate ion).It has been reported that the physicochemical properties of hydrotalcite-like compounds can be easily tuned by changing the nature and amount of metal cations and anions and the most typical and widely used one is MgAl hydrotalcite [13,14].After calcination of MgAl hydrotalcites at 723–773K,MgAl mixed oxides with a poor crystallized MgO-type structure will be obtained.When the calcination temperature reaches 1100K or above,the formation of MgAl 2O 4spinel phase can also be observed [13,15].Early studies have proved that,MgAl mixed oxides derived from hydrotalcite precursors possess a large SO x adsorption capacity,forming moderately stable sulfates that can be decomposed in cracking zone (reactor).Further,incorporation of transition metal oxides such as those of Ce,Cu,Fe,Co,V and Cr as promoters (promote the oxidation of SO 2to SO 3that is easier to be adsorbed and the reduction of sulfates formed)to hydrotalcite precursors is also necessary.The calcined basic compounds with redox property,good thermal stability and abrasion resistance,have been considered as a class of promising SO x transfer materials [1–5,10,16,17].Many previous studies mainly focused on tuning species and content of active components of SO x transfer additives,however taking into account catalytic applications,properties such as high surface area,small crystallite size and more active sites are also very important.Preparation of porous,structu-rally ordered oxides using organic molecules as templates or structure-directing agents have been attracted much interest [18–25].Some of them showed an ordered,well-de ﬁned pore size,even after calcination [18–21].Others had no regular pore system but a high surface area [22,23].By this approach,a lot of metal oxides with potential catalytic applications were prepared,including Al 2O 3[25],MgO [23],CeO 2[22],MgAl 2O 4[24]and so on.Cerium and copper have been proved to be excellent promoters in SO x transfer catalysts [26–32].In this research,on the basis of MgAl adsorbent,cerium and copper oxides were incorporated into the SO x transfer additives.Further,a modi ﬁed precipitation method via CTAB surfactant assisted route for synthesis of high-surface-area porous CuMgAlCe mixed oxides was employed.After preparation,these samples were tested for catalytic SO 2removal under the conditionssimilar to those of FCC units and the in ﬂuences of chemical composition and surfactant/metal molar ratio on the structural properties and further catalytic performance were investigated.For comparation,MgAl,MgAlCe and CuMgAl mixed oxides were also prepared.2.Experimental 2.1.MaterialsAluminum nitrate (Al(NO 3)3Á9H 2O),magnesium nitrate (Mg (NO 3)2Á6H 2O),Cetyltrimethylammonium bromide (CTAB)and sodium hydroxide (NaOH)were used as starting materials.2.2.Sample preparationCuMgAlCe samples were synthesized as following steps:stoichiometric amounts of magnesium nitrate,aluminum nitrate and desired amount of CTAB were added to well stirring deionized water.After that,with quick stirring,Na 2CO 3/NaOH solution was added dropwise to the slurry to produce the viscous liquid mixture (pH =10).The slurry was stirred for another 30min and then aged at 353K for 24h.The mixture was then cooled to room temperature,ﬁltered and washed until the pH of wash water is 7.The solid product was dried at 373K for 24h and then calcined at 1023K for 4h.For comparation,MgAl,MgAlCe and CuMgAl mixed oxides were also prepared through a conventional coprecipitation method,also using Na 2CO 3/NaOH as precipitant.More information about molar ratios is described in Table 1.2.3.CharacterizationPowder X-ray diffraction patterns were obtained on a Rigaku D/MAX-rA diffractometer employing Cu K αradiation (the wavelength is 0.15406nm)operated at 40kV and 40mA.Surface area and pore distribution measurements were con-ducted by N 2adsorption –desorption in ASAP2020apparatus,using the Brunauer –Emmett –Teller (BET)method for surface area and Brunauer –Joyner –Hallenda (BJH)method for pore distribution calculation.Prior to the analysis,the samples were outgassed in a vacuum (10À5Torr)at 693K for 5h.Thermal decomposition of the as-synthesized hydrotalcite precursors was evaluated by TG/DTA analysis performed on a TATable 1Molar ratios of the prepared solids.Sample Mg/Al (mol/mol)Cu (wt%)Ce (wt%)CTAB/Metal (mol/mol)MgAl 3000MgAlCe 3080CuMgAl 3500CuMgAlCe-03580CuMgAlCe-0.053580.05CuMgAlCe-0.13580.1CuMgAlCe-0.23580.2H.-T.Kang et al./Ceramics International 40(2014)5357–53635358Thermobalance SDTQ600,operating under dry airﬂow at10K minÀ1heating rate up to1073K.2.4.Catalytic testThe SO2-uptake reaction was investigated in a microreactorcomprised of a quartz tube(i.d.¼10mm)and a tube furnaceused as a heating device.30mg catalyst with a particle sizefrom110to280m m wasﬁxed in the middle of tube with quartz ﬁbers,and a stream of60mL minÀ1with3000ppm of SO2, 5.05%(v/v)O2and He balance was passed over it.Theadsorption cycle wasﬁnished after a time on stream of35min at1003K.For catalyst regeneration(reduction step),the system was reduced in a stream of60mL minÀ1of H2for10min at923K.To disclose reusability of the catalysts,fouradsorption–reduction cycles were carried out.SO2in efﬂuentgas was selectively adsorbed by H2O2solution,in which SO2can be converted to sulfuric acid(H2SO4).The sulfuric acid wastitrated with sodium hydroxide standard solution using methylred-methylene blue as indicator,allowing us to get the SO2amount by calculating consumption of sodium hydroxide[33].3.Results and discussion3.1.Physicochemical characteristicsThe XRD patterns of as-synthesized precursors and oxidesare illustrated in Fig.1.Before calcination,the reﬂections aresharp and intense at low diffraction angles while less intense athigher angles,conﬁrming the presence of hydrotalcite phasewith layered structure(LDH)in carbonate form(peaks close to2θ¼111,231,341,601,ascribed to diffraction by basal planes(003)(006)(012)and(110)respectively)[34].No Cu(OH)2orCuO phase was observed,suggesting the complete incorpora-tion of Cu into the layered crystalline structure.At2θ¼28.71,there is a speciﬁc diffraction attributed to CeO2formed fromCe(OH)3,indicating Ce3þwas not easily incorporated intohydrotalcite phase[7].Although CeO2is not comprised in thelayer structure,it still plays an important role in the catalyst.After calcination at1023K for4h,the hydrotalcite layered structure all collapsed and new crystalline phases formed.As reported earlier,when a MgAl hydrotalcite is calcined at the temperature above673K and below1273K,only the MgO (periclase)phase is detected[35],that has been proved again by XRD patterns in Fig.1(reﬂections at2θ¼36.8–371,42.9–43.11,62.4–62.61).Obviously,the incorporation of CTAB decreased the crystallinity,however amount of CTAB had no regular inﬂuence on the crystalline phase.The patterns of oxides also show that there are no characteristic XRD peaks associated with Cu species,indicating a good dispersion of CuO in the samples.Similarly,CeO2phase was detected again due to its segregation from main phase.Fig.2shows the TG/DSC curves of all hydrotalcite-like precursors and two weightlessness regions can be obviously observed.While below503K,only interlayer water,crystallization water and physical absorbed water are lost which has no obvious inﬂuence on layered structures of the hydrotalcite-like compounds. When heated to523–723K,OHÀin brucite-like sheets and CO32Àin interlayer space will be transformed to H2O and CO2,namely dehydroxylation and decarbonation,and layered structure would be destroyed above this temperature range[36,37].It can be observed that theﬁrst weightlessness stage occurs at498K(weight loss of 19.7%),484K(weight loss of13.5%),462K(weight loss of 12.1%)for MgAl,MgAlCe and CuMgAlCe-0respectively.In second weightlessness stage,maximum weight loss of MgAl, MgAlCe and CuMgAlCe-0appeared at665K(weight loss of 36.5%),662K(weight loss of32.1%)and637K(weight loss of 30.5%)paring with MgAl,lower endothermic peak temperature for MgAlCe and CuMgAlCe-0samples indicates that incorporation of Ce and Cu will slightly degrade thermal stability of hydrotalcite-like compounds,which may due to the abatement of interaction between sheets and interlayer spacing.As to CuMgAlCe-0.1,there are three major peaks,two of which are endothermic(consistent with former three samples)and the other is exothermic peak occurs at503K,which may be attributed to the oxidation of organic residues and decomposition of nitrates.The speciﬁc surface area,pore volume and average pore size of the calcined solids are summarized in Table2.All solids display high surface area and the pore diameter of allsamples Fig.1.XRD patterns of the hydrotalcite-like precursors and calcined oxides;(a)MgAl,(b)MgAlCe,(c)CuMgAl,(d)CuMgAlCe-0,(e)CuMgAlCe-0.05, (f)CuMgAlCe-0.1,(g)CuMgAlCe-0.2H.-T.Kang et al./Ceramics International40(2014)5357–53635359fell in the mesopore range.It can be seen that the molar ratio of surfactant to metal has a signiﬁcant inﬂuence on the speciﬁc surface area and the highest is142m2gÀ1for sample CuMgAlCe with a surfactant/metal molar ratio of0.1.When the molar ratio is higher than0.1,the speciﬁc surface area would decrease while the pore size increase.That is because the much heat and gas from CTAB decomposition could destroy the pore walls and then increased the pore size,which led to a decrease in speciﬁc surface area.The N2adsorption–desorption isotherms of the calcined samples(Fig.3)show that all are of type IV,which are typical characteristic of mesoporous materials.No point B is observed in all samples,indicating that multilayer adsorption process took place at the beginning.According to IUPAC classiﬁca-tion,the hysteresis loop belongs to type H3,due to the physical phenomenon of capillary condensation in mesopores. This type of hysteresis is usually found in materials consisted of aggregates or agglomerates of particles forming slit shaped pores(plates or edged particles like cubes).Fig.4shows the pore size distributions of these samples determined by BJH method employing adsorption branches. It is shown that in all cases the pore size largely fell in the range of10–100nm,exhibiting relatively broad distributions. As can be seen for CuMgAlCe calcined samples,the pore size distribution shifts to larger values with the increasing CTAB/ metal ratios,due to the destruction of the pore walls by the decomposition of CTAB as mentioned above[38].3.2.Catalytic testMixed gas(1.8L)was passed over30mg catalysts at aﬂow rate of60mL minÀ1at1003K and the reaction time is just 30min.The outlet gas was adsorbed by H2O2solution and tested by titration method.In order to disclose the reusability of solid samples,four adsorption–reduction cycles were carried out and the solid was reduced for10min with a H2ﬂow (60mL minÀ1)at923K after every oxidativeadsorption.Fig.2.TGA/DSC analysis of the hydrotalcite precursors.Table2Structural properties of the calcined samples.Sample BET area(m2gÀ1)Pore volume(cm3gÀ1)Pore diameter(nm)Average particle size(nm) MgAl120.70.6821.3849.72MgAlCe127.80.7017.9046.96CuMgAl156.70.6112.4338.29CuMgAlCe-0133.80.6014.0944.85CuMgAlCe-0.05142.10.7216.4842.19CuMgAlCe-0.1142.20.7116.5242.18CuMgAlCe-0.2125.60.8622.0447.78H.-T.Kang et al./Ceramics International40(2014)5357–53635360The SO 2uptake capacity upon four oxidative adsorption of prepared material is shown in Table 3.It is found that adsorption is highly in ﬂuenced by the chemical composition of catalysts.According to Cycle I data,the SO 2pickup capacity of MgAl is higher than CuMgAl and MgAlCe.However,regenerability of MgAl is very limited,achieving only 79%after the second cycle at 923K.This can also be signi ﬁcantly re ﬂected in adsorption capacity for Cycle III and Cycle IV,suggesting promotion effect of Ce or Cu oxides on SO 2adsorption capacity.Moreover,it can be observed that both incorporation of Ce and Cu slightly improved the capacity,comparing with MgAl.This may be due to the dual effects of structural properties and synergistic promotion.As to CuMgAlCe samples with different CTAB/metal ratios,the catalytic activity also shows difference.When CTAB/metal ratio reached 0.1,the SO 2uptake capacity reached the highest 4231.3m g (Cycle I),about removing 38%of SO 2in mixed gas.Its best bene ﬁcial effect on oxidative adsorption can be assigned to the textural properties (Table 2).High speci ﬁc surface area would provide more adsorption sites and exposed active sites,which is bene ﬁcial for SO x adsorption and SO 2oxidationrespectively.Fig.3.N 2adsorption –desorption isotherms of calcinedoxides.Fig.4.Pore size distributions of calcined oxides.Table 3SO 2uptake upon four adsorption –reduction cycles.sampleTotal SO 2(m g/30min)Adsorbed SO 2(m g/30min)Regeneration (%)aCycle ICycle II Cycle III Cycle IV 123MgAl 11,1103079.22772.12187.61522.3907969MgAlCe 11,1102753.32676.32325.81862.7978780CuMgAl 11,1102933.12999.52708.42294.21009085CuMgAlCe-011,1103152.43133.52753.12360.9998886CuMgAlCe-0.0511,1104151.84214.93806.03234.81009085CuMgAlCe-0.111,1104231.34201.83653.23116.2998785CuMgAlCe-0.211,1103796.43805.73441.62890.91009084aRegeneration 1,2,and 3are calculated by CycleII/CycleI,CycleIII/CycleII,CycleIV/CycleIII,respectively.H.-T.Kang et al./Ceramics International 40(2014)5357–53635361However,higher CTAB/metal ratio could decrease the adsorption capacity due to the decrease of speci ﬁc surface area.For the lifetime of a given additive,regenerability is very crucial,it can be seen that CuMgAlCe samples possess good regeneration capacity,especially for sample CuMgAlCe-0.1,the SO 2uptake capacity still reached 3116.2m g after the fourth oxidative adsorption.SO 2transfer additives used in FCC units must have high adsorption rates,to achieve suitable SO x adsorption in short time.For this,SO 2adsorption test was carried out again by contacting 30mg catalyst with the mixed gas (60mL min À1),and the SO 2instantaneous concentration in tail gas along with time is shown in Fig.5.Fig.5presents that almost all the samples exhibit the highest adsorption rate at about ﬁrst 15min,which is desirable since catalyst's residence time in the regenerator of FCC process is very short (about 5–15min),depending on its operation mode (partial or total combustion respectively).Obviously,CuMgAlCe-0also shows the highest adsorption rate in ﬁrst 15min comparing with MgAl,CuMgAl and MgAlCe.The SO 2adsorption rate decreased with elapsed time in accordance the progress of the chemisorption.The SO 2adsorption rate of all samples almost dropped to the same level,approximately 25–50m g SO 2min À1after 60min.For those catalysts synthesized by surfactant-assisted route,the CuMgAlCe-0.1displayed the highest SO 2adsorptionrate,and followed by CuMgAlCe-0.05,CuMgAlCe-0.2and CuMgAlCe-0.The catalytic behavior of the samples could be assigned to their textural properties determined by different synthetic conditions and CuMgAlCe-0.1with the best bene ﬁcial structural properties could provide more chemisorption sites,which is desired for SO 2abatement.Fig.6presents the adsorption rate of CuMgAlCe-0.1upon three cycles.After third cycle the sample CuMgAlCe-0.1still shows a high SO 2uptake rate at ﬁrst 15min,processing stable SO 2removal performance under FCC reaction and regeneration conditions.4.ConclusionsHigh-surface-area CuMgAlCe mixed oxides prepared by a surfactant-assisted method were proposed to be applied as SO x transfer additives for SO x removal in FCC units and the effects of surfactant (CTAB)to metal molar ratio on the structural properties and catalytic activity were investigated.The pre-cursors exhibited hydrotalcite-like structures,determined by XRD and TG/DSC characterization.N 2adsorption –desorption analysis showed that CuMgAlCe-0.1(the CTAB/metal molar ratio is 0.1)mixed oxide possessed the highest speci ﬁc surface area and higher ratio would decrease the speci ﬁc surface area.MgAl,MgAlCe,CuMgAl and CuMgAlCe mixed oxides (hydrotalcite-like precursors calcined at 1023K)were all tested for SO 2removal under the conditions similar to those of FCC units.CuMgAlCe-0mixed oxide with incorporation of both Ce and Cu showed highest adsorption capacity and rate than MgAl,CuMgAl and MgAlCe.Addition of CTAB during synthetic process also had a signi ﬁcant in ﬂuence on catalytic performance of CuMgAlCe mixed oxides and CuMgAlCe-0.1with the highest surface area presented the best SO 2removal performance probably due to its more chemisorption sites,which is bene ﬁcial for SO 2abatement.Besides,these catalysts still have satisfactory SO 2removal performance after four adsorption –reduction cycles and desirable adsorption rate,which is very applicable for SO 2abatement in FCC units.AcknowledgmentsWe gratefully appreciate the ﬁnancial support from Petro-China Innovation Foundation(2012D-5006-0401).Fig.5.SO 2adsorption curve of mixedoxides.Fig.6.SO 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片状铋钒酸铋复合催化剂的制备及其光催化性能

Vol.53 No.1Jan.,2021第 53 卷第 1 期2021年1月无机盐工业INORGANIC CHEMICALS INDUSTRYDoi:10.11962/1006-4990.2020-0064]开放科学(资源服务)标志识码(OSID)片状铋/钒酸铋复合催化剂的制备及其光催化性能冯飞「,李书文1,汪铁林1,2,王为国匕王存文1'2(1.武汉工程大学化工与制药学院,湖北武汉430205 ； 2.武汉工程大学绿色化工过程教育部重点实验室)摘要：用溶剂热法合成了一系列不同铋含量的片状铋/钒酸铋(Bi/BiVO 4)复合光催化剂。

采用X 射线衍射 (XRD)、X 射线光电子能谱(XPS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)、紫夕卜-可见漫反射光谱(UV-vis DRS)、电感耦合等离子发射光谱(ICP-OES)、氮气吸附脱附和光电流响应等技术对所制备的催化剂进行了表征。

通过氙灯下光催化降解亚甲基蓝的性能来评价样品的光催化活性，实验结果表明铋的自掺杂能显著提高钒酸铋的光催化活性。

最后，通过自由基捕获实验对铋/钒酸铋光催化机理进行了探讨。

关键词:钒酸铋;复合半导体;光催化;染料降解中图分类号：0643.36 文献标识码:A 文章编号：1006-4990(2021)01-0107-06Synthesis and photocatalytic performance of sheet -like Bi/BiVO 4 composite catalystFeng Fei 1, Li Shuwen 1, Wang Tielin 1,2, Wang Weiguo 1,2, Wang Cunwen 1,2(1.School of Chemical Engineering and Pharmacy , Wuhan Institute of Technology , Wuhan 430205,China ；2.Key Laboratory of Green Chemical Engine e ring Proces s of M inistry ofEducation , Wuhan Institute of Technology )Abstract ： A series of sheet-like Bi/BiVO 4 composite photocatalysts with different Bi contents were synthesized using solvo thermal method.The prepared catalysts were characterized by using X-ray diffraction (XRD ), X-ray photoelectron spectro-scopy ( XPS ), scanning electron microscopy (SEM ), transmission electron microscopy ( TEM ), ultraviolet-visible diffuse reflec tion spectroscopy (UV -Vis DRS ), inductively coupled plasma optical emission spectroscopy (ICP-OES ), nitrogen adsorp tion-desorption analysis and photocurrent response measurements.The photocatalytic performance of the sample was assessed by photodecomposition of methylene blue (MB ) under xenon lamp irradiation.The results showed that the photocatalytic ac tivity of BiVO 4 was enhanced significantly with Bi self-doping.Finally , the photocatalytic reaction mechanism of Bi/BiVO 4composite was discussed by free radical capture experiments.Key words : bismuth vanadate 曰 composite semiconductor ； photocatalysis 曰 dye degradation单斜相钒酸铋(BiV04)具有价廉、无毒等优点咱1］,是一种优良的光催化材料。

高分子论文参考文献

Published:May 12,2011COMMUNICATION /JACSInterface-Directed Assembly of One-Dimensional Ordered Architecture from Quantum Dots Guest and Polymer HostShengyang Yang,Cai-Feng Wang,and Su Chen*State Key Laboratory of Materials-Oriented Chemical Engineering,and College of Chemistry and Chemical Engineering,Nanjing University of Technology,Nanjing 210009,P.R.ChinabSupporting Information ABSTRACT:Assembly of inorganic semiconductor nano-crystals into polymer host is of great scienti ﬁc and techno-logical interest for bottom-up fabrication of functional devices.Herein,an interface-directed synthetic pathway to polymer-encapsulated CdTe quantum dots (QDs)has been developed.The resulting nanohybrids have a highly uniform ﬁbrous architecture with tunable diameters (ranging from several tens of nanometers to microscale)and enhanced optical performance.This interfacial assembly strategy o ﬀers a versatile route to incorporate QDs into a polymer host,forming uniform one-dimensional nanomaterials po-tentially useful in optoelectronic applications.Similar to the way that atoms bond to form molecules and complexes,inorganic nanoparticles (NPs)can be combined to form larger ensembles with multidimensional ordered hier-archical architecture,evoking new collective functions.To this end,the development of the controlled self-assembly method for well-de ﬁned structures of these ensembles is signi ﬁcant for creating new and high-performance tunable materials and hence has aroused appealing scienti ﬁc and industrial interest.1Particu-larly,much e ﬀort has been devoted to the construction of one-dimensional (1D)structures of NPs,owing in part to their application as pivotal building blocks in fabricating a new generation of optoelectronic devices.2In this context,directed host Àguest assembly of NPs into polymer matrices is an e ﬀective “bottom-up ”route to form 1D ordered functional materials with advantageous optical,electrical,magnetic,and mechanical properties.3Some typical routes have been developed for the generation of these 1D hybrids so far,involving template-assisted,4seeding,5and electro-static approaches.6However,the challenge still remains to precisely manipulate assembly of aqueous NPs and water-insoluble polymers into uniform 1D nanocomposites with a high aspect ratio because of phase separation and aggregation.7Moreover,facile synthetic strate-gies are highly needed to fabricate homogeneous 1D composites in which each component still preserves favorable properties to produce optimal and ideal multifunctional materials.A liquid Àliquid interface o ﬀers an ideal platform to e ﬃciently organize NPs into ordered nanostructures driven by a minimiza-tion of interfacial energy.8While much of this research has been directed toward NP hybrids with diverse morphologies based on small organic ligand-directed assembly,9some success has also been achieved in polymer-based NPs nanocomposites.10Russelland co-workers developed ultrathin membranes and capsules of quantum dots (QDs)stabilized by cross-linked polymers at the toluene/water interface.10a,11Brinker ’s group reported the fab-rication of free-standing,patternable NP/polymer monolayer arrays via interfacial NP assembly in a polymeric photoresist.12Herein,a simple host Àguest assembly route is developed to facilely create homogeneous 1D CdTe/polymer hybrids without any indication of phase separation at the aqueous/organic inter-face for the ﬁrst time.The CdTe nanocrystal is a semiconductor that has been used extensively for making thin ﬁlm for solar cells.13Some elegant studies have been made in synthesizing pure inorganic 1D CdTe nanowires via assembly from corre-sponding individual CdTe nanocrystals.14In this work,CdTe QDs are covalently grafted with poly(N -vinylcarbazole-co -glycidylmethacrylate)(PVK-co -PGMA)to form uniform ﬁbrous ﬂuorescent composites at the water/chloroform interface via the reaction between epoxy groups of PVK-co -PGMA and carboxyl groups on the surface of CdTe QDs (Scheme 1).15These 1D composite ﬁbers can be allowed to grow further in the radial direction by “side-to-side ”assembly.Additionally,this type of interfacial QD Àpolymer assembly can observably improve the ﬂuorescence lifetime of semiconductor QDs incorporated in theScheme 1.Schematic Representation of the Synthesis of PVK-co -PGMA/CdTe QDs Composite Nano ﬁbersReceived:February 8,2011polymeric matrix.It can be expected that this example of both linear axial organization and radial assembly methodology can be applied to fabricate spatial multiscale organic Àinorganic com-posites with desired properties of NPs and polymers.Figure 1a shows a typical scanning electron microscope (SEM)image of PVK-co -PGMA/CdTe QDs composite nano ﬁ-bers obtained at the water/chloroform interface after dialysis.The as-prepared ﬁbers have uniform diameters of about 250nm and typical lengths in the range of several tens to several hundreds of micrometers (Figures 1a and S4Supporting In-formation [SI]).Interestingly,PVK-co -PGMA/CdTe composite ﬁbers can randomly assemble into nestlike ring-shaped patterns (Figures 1b and S5[SI]).Given the interaction among epoxy groups,the formation of nestlike microstructures could be attributed to incidental “head-to-tail ”assembly of composite ﬁbers.Moreover,in order to establish the relationship between the role of epoxy groups and the formation of composite nano ﬁbers,control experiments were performed,in which pure PGMA or PVK was used to couple CdTe QDs.The PGMA/CdTe composites could be obtained with ﬁbrous patterns (Figure S6[SI]),but no ﬁbrous composites were achieved at the biphase interface with the use of PVK under the same conditions.The microstructures and ﬂuorescence properties of PVK-co -PGMA/CdTe composite ﬁbers were further character-ized using laser confocal ﬂuorescence microscopy (LCFM).Confocal ﬂuorescence micrographs of composite ﬁbers show that the di ﬀerently sized QDs have no obvious in ﬂuence on the morphology of composites (Figure 1c Àe).Clearly,uniform and strong ﬂuorescence emission is seen throughout all the samples,and the size-dependent ﬂuorescence trait of CdTe QDs in PVK-co -PGMA matrix remains well.In order to verify the existence and distribution of CdTe QDs in the ﬁbers,transmission electron microscopy (TEM)was employed to examine the assembled structures.Figure 2a shows a TEM image of PVK-co -PGMA/CdTe QDs composite nano ﬁ-bers,indicating each composite ﬁber shown in Figure 1a was assembled from tens of ﬁne nano ﬁbers.An individual ﬁne nano ﬁber with the diameter of about 30nm is displayed in Figure 2b,from which we can see that CdTe QDs have been well anchored into the ﬁber with polymeric protection layer,revealing this graft-form process at the interface e ﬀectively avoidednon-uniform aggregation in view of well-dispersed CdTe QDs within the composite ﬁber,consistent with the LCFM observa-tion.Unlike previous works where the nanoparticles were ad-sorbed onto the polymer ﬁbers,16CdTe QDs were expelled from the surface of ﬁbers (∼2.5nm)in our system (Figure 2c),albeit the high percentage of QDs in the polymer host (23wt %)was achieved (Figure S7[SI]).This peculiarity undoubtedly confers CdTe QDs with improved stability.The clear di ﬀuse rings in the selected area electron di ﬀraction (SAED)pattern further indicate excellent monodispersion and ﬁnely preserved crystalline struc-ture of QDs in the nano ﬁbers (Figure 2d).The SAED data correspond to the cubic zinc blende structure of CdTe QDs.A possible mechanism for the assembly of 1D nanostructure was proposed,as illustrated in Figure S8[SI].The hydrophilic epoxy groups of the PVK-co -PGMA chain in the oil phase orient toward the biphase interface and then react with carboxyl groups on the surface of CdTe QDs in the aqueous phase to a ﬀord premier PVK-co -PGMA/CdTe QDs composites.Such nanocomposites will reverse repeatedly,resulting from iterative reaccumulation of epoxy groups at the interface and the reaction between the active pieces (i.e.,epoxy or carboxyl groups)in the composites with intact CdTe QDs or PVK-co -PGMA,forming well-de ﬁned nano-ﬁbers.The control experiments showing that the diameter of composite ﬁbers increases with the increase in the concentration of PVK-co -PGMA are in agreement with the proposed mechan-ism (Figure S9[SI]).In addition,it is expected that the pure polymeric layer on the surface of the ﬁbers (red rectangular zone in Figure 2c)will allow further assembly of ﬁne ﬁbers into thick ﬁbers,and these ﬁbers also could randomly evolve into rings,forming nestlike microstructures when the “head ”and “tail ”of ﬁbers accidentally meet (Figure 1b).To further examine the assembly behavior of composite ﬁbers,the sample of PVK-co -PGMA/CdTe QDs composite nano ﬁbers were kept at the water/chloroform interface for an additional month in a close spawn bottle at room temperature (Figure S10[SI]).With longer time for assembly,thicker composite ﬁbers with tens of micrometers in diameter were obtained (Figure 3a).These micro-ﬁbers have a propensityto form twisted morphology (Figure 3a,b),Figure 1.(a,b)SEM images of PVK-co -PGMA/CdTe QDs composite nano ﬁbers.(c Àe)Fluorescence confocal microscopy images of PVK-co -PGMA/CdTe QDs composite nano ﬁbers in the presence of di ﬀerently sized QDs:(c)2.5nm,(d)3.3nm,and (e)3.6nm.The excitation wavelengths are 488(c),514(d),and 543nm (e),respectively.Figure 2.(a,b)TEM images of PVK-co -PGMA/CdTe QDs composite nano ﬁbers,revealing composite nano ﬁber assemblies.(c)HRTEM image and (d)SAED pattern of corresponding PVK-co -PGMA/CdTe QDs composite nano ﬁbers.while their re ﬁned nanostructures still reveal relatively parallel character and con ﬁrm the micro ﬁbers are assembled from countless corresponding nano ﬁbers (Figure 3c).The corresponding LCFM image of an individual micro ﬁber is shown in Figure 3d (λex =488nm),indicating strong and homogeneous green ﬂuorescence.Another indication is the ﬂuorescent performance of PVK-co -PGMA/CdTe QDs composite micro ﬁbers (Figure 4a).The ﬂuorescent spectrum of composite ﬁbers takes on emission of both PVK-co -PGMA and CdTe QDs,which suggests that this interfacial assembly route is e ﬀective in integrating the properties of organic polymer and inorganic nanoparticles.It is worth noting that there is a blue-shift (from 550to 525nm)and broadening of the emission peak for CdTe QDs upon their incorporation into polymeric hosts,which might be ascribed to the smaller QD size and less homogeneous QD size distribution resulting from the photooxidation of QD surfaces.17Since the emission spectra of PVK-co -PGMA spectrally overlap with the CdTe QD absorption (Figure S11[SI]),energy transfer from the copolymer to the CdTe QDs should exist.18However,the photoluminescence of PVK-co -PGMA does not vanish greatly in the tested sample in comparison with that of polymer alone,revealing inferior energy transfer between the polymer host and the QDs.Although e ﬃcient energy transfer could lead to hybrid materials that bring together the properties of all ingredients,18it is a great hurdle to combine and keep the intrinsic features of all constituents.19In addition,by changing the polymeric compo-nent and tailoring the element and size of QDs,it should be possible to expect the integration of organic and inorganic materials with optimum coupling in this route for optoelectronic applications.Finally,to assess the stability of CdTe QDs in the composite micro ﬁbers,time-resolved photoluminescence was performed using time-correlated single-photon counting (TCSPC)parative TCSPC studies for hybrid PVK-co -PGMA/CdTe QDs ﬁbers and isolated CdTe QDs in the solid state are presented in Figure 4b.We can see that the presence of PVK-co -PGMA remarkably prolongs the ﬂuorescence lifetime (τ)of CdTe QDs.Decay traces for the samples were well ﬁttedwith biexponential function Y (t )based on nonlinear least-squares,using the following expression.20Y ðt Þ¼R 1exp ðÀt =τ1ÞþR 2exp ðÀt =τ2Þð1Þwhere R 1,R 2are fractional contributions of time-resolved decaylifetimes τ1,τ2and the average lifetime τhcould be concluded from the eq 2:τ¼R 1τ21þR 2τ22R 1τ1þR 2τ2ð2ÞFor PVK-co -PGMA/CdTe QDs system,τh is 10.03ns,which is approximately 2.7times that of isolated CdTe QDs (3.73ns).Photooxidation of CdTe QDs during the assembly process can increase the surface states of QDs,causing a delayed emission upon the carrier recombination.21Also,the polymer host in this system could prevent the aggregation of QDs,avoid self-quench-ing,and delay the ﬂuorescence decay process.22The increased ﬂuorescence lifetime could be also ascribed to energy transfer from PVK-co -PGMA to CdTe QDs.18c The result suggests that this host Àguest assembly at the interface could ﬁnd signi ﬁcant use in the fabrication of QDs/polymer hybrid optoelectronic devices.In summary,we have described the ﬁrst example of liquid/liquid interfacial assembly of 1D ordered architecture with the incorporation of the QDs guest into the polymer host.The resulting nanohybrids show a highly uniform ﬁbrous architecture with tunable diameter ranging from nanoscale to microscale.The procedure not only realizes the coexistence of favorable properties of both components but also enables the ﬂuorescence lifetime of QDs to be enhanced.This interesting development might ﬁnd potential application for optoelectronic and sensor devices due to high uniformity of the 1D structure.Further e ﬀorts paid on optimal regulation of QDs and polymer composition into 1D hybrid nanostructure could hold promise for the integration of desirable properties of organic and inorganic compositions for versatile dimension-dependent applications.In addition,this facile approach can be easily applied to various semiconductor QDs and even metal NPs to develop highly functional 1D nanocomposites.’ASSOCIATED CONTENTbSupporting Information.Experimental details,FT-IR,GPC,UV Àvis,PL,SEM,TGA analysis,and complete ref 9c.This material is available free ofcharge via the Internet at .Figure 3.(a,b)SEM and (c)FESEM images of PVK-co -PGMA/CdTe QDs composite micro ﬁbers.(d)Fluorescence confocal microscopy images of PVK-co -PGMA/CdTe QDs composite micro ﬁbers inthe presence of green-emitting QDs (2.5nm).Figure 4.(a)Fluorescence spectra of PVK-co -PGMA,CdTe QD aqueous solution,and PVK-co -PGMA/CdTe QDs composite micro-ﬁbers.(b)Time-resolved ﬂuorescence decay curves of CdTe QDs (2.5nm diameter)powders (black curve)and the corresponding PVK-co -PGMA/CdTe QDs composite micro ﬁbers (green curve)mea-sured at an emission peak maxima of 550nm.The samples were excited at 410nm.Biexponential decay function was used for satisfactory ﬁtting in two cases (χ2<1.1).’AUTHOR INFORMATIONCorresponding Authorchensu@’ACKNOWLEDGMENTThis work was supported by the National Natural Science Foundation of China(21076103and21006046),National Natural Science Foundation of China-NSAF(10976012),the Natural Science Foundations for 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制备条件对铜铬催化剂酸性质的影响

ａｎａｌｙｓｉｓ，ｉｔｉｓｉｎｄｉｃａｔｅｄｔｈａｔｉｎｔｈｅａｍｏｒｐｈｏｕｓｃａｔａｌｙｓｔｓ，ｔｈｅａｃｉｄｉｃｓｉｔｅｓａｒｅｐｒｏｖｉｄｅｄｍｅｒｅｌｙｂｙＣｕＯａｎｄＣｒ２Ｏ，ｗｈｉｌｅｉｎｔｈｅｃｒｙｓｔａｌｓａｍｐｌｅｓ，ｔｈｏｓｅｃｏｍｐｏｓｅｄｏｆｂｏｔｈｔｈｅｏｘｉｄｅｓｔｈｅｍｓｅｌｖｅｓａｎｄｉｎｃｒｅａｓｅｍｅｎｔｏｆＢａｃｉｄｉｃｓｉｔｅｓｃａｕｓｅｄｂｙｔｈｅａｓｙｍｍｅｔｒｉｃａｌｍｉｘｔｕｒｅｏｆＣｕＯａｎｄＣｒ２Ｏ３，ｗｈｉｃｈｆｕｒｔｈｅｒｉｌｌｕｓｔｒａｔｅｄｔｈａｔｗｉｔｈｔｈｅｃｒｙｓｔａｌｓｉｚｅｏｆｏｘｉｄｅｓｄｅｃｒｅａｓｉｎｇ，ｔｈｅｐａｒｔｉｃｌｅｓｂｅｃａｍｅｗｅｌｌ — ｄｉｓｔｒｉｂｕｔｅｄ，ｔｏｇｅｔｈｅｒｗｉｔｈｔｈｅｄｅｃｒｅａｓｉｎｇｏｆａｃｉｄｉｃｐｒｏｐｅｒｔｉｅｓｏｆｔｈｅｃａｔａｌｙｓｔｓａｎｄＢａｃｉｄｒａｔｉｏ，ａｎｄｖｉｃｅｖｅｒｓａ．
（ＦｕｓｈｕｎＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅｏＪＰｅｔｒｏｌｅｕｍａｎｄＰｅｔｒｏｃｈｅｍｉｃａｌｓ，ＳＩＮＯＰＥＣ，ＦｕｓｈｕｎＬｉａｏｎｉｎｇ１１３００１，Ｃｈｉｎａ）

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Ａｖａｉｌａｂｌｅ　ｏｎｌｉｎｅ　ａｔ　ｗｗｗ．ｓｃｉｅｎｃｅｄｉｒｅｃｔ．ｃｏｍ　８ＣＩＥＮＣＥ　ＤＩＲＥＣ１１－０　

Ｊｏｕｒｎａｌ　ｏｆ　Ｎａｔｕｒａｌ　Ｇａｓ　Ｃｈｅｍｉｓｔｒｙ　１５（２００６）１４４—１４８　Ａｒｔｉｃｌｅ　ＳＣＩＥＮＣＥ　ＰＲＥＳＳ　

Ｅｆｆｅｃｔ　ｏｆ　Ｃｒ　ａｎｄ　Ｃｏ　Ｐｒｏｍｏｔｅｒｓ　Ａｄｄｉｔｉｏｎ　ｏｎ　Ｖａｎａｄｉｕｍ　Ｐｈｏｓｐｈａｔｅ　Ｃａｔａｌｙｓｔｓ　ｆｏｒ　Ｍｉｌｄ　Ｏｘｉｄａｔｉｏｎ　ｏｆ佗．Ｂｕｔａｎｅ　

Ｙｕｎ　Ｈｉｎ　Ｔａｕｆｉｑ－Ｙａｐ　Ｐｕｔｒａ　Ｌａｂｏｒａｔｏｒｙ　ｊｏＴ　Ｃａｔａｌｙｓｉｓ　ａｎｄ　Ｔｅｃｈｎｏｌｏｇｙ．Ｄｅｐａｒｔｍｅｎｔ　ｏｆ　Ｃｈｅｍｉｓｔｒｙ　Ｆａｃｕｌｔｙ　ｏｆ　Ｓｃｉｅｎｃｅ　Ｕｎｉｖｅｒｓｉｔｉ　Ｐｕｔｒａ　Ｍａｌａｙｓｉａ　４３４Ｏ０　ＵＰＭ　Ｓｅｒｄａｎｇ．Ｓｅｌａｎｇｏｒ，Ｍａｌａｙｓｉａ．　［Ｍａｎｕｓｃｒｉｐｔ　ｒｅｃｅｉｖｅｄ　Ｊａｎｕａｒｙ　２０，２００６；ｒｅｖｉｓｅｄ　Ｍａｒｃｈ　２５，２００６］　

Ａｂｓｔｒａｃｔ：　Ｉｎ　ｔｈｉｓ　ｓｔｕｄｙ，Ｃｒ　ａｎｄ　Ｃｏ　ｐｒｏｍｏｔｅｄ，ａｓ　ｗｅｌｌ　ａｓ　ｕｎｐｒｏｍｏｔｅｄ　ｖａｎａｄｉｕｍ　ｐｈｏｓｐｈａｔｅ（ＶＰＯ）　

ｃａｔａｌｙｓｔｓ　ｗｅｒｅ　ｓｙｎｔｈｅｓｉｚｅｄ　ｂｙ　ｔｈｅ　ｒｅａｃｔｉｏｎ　ｏｆ　Ｖ２Ｏ５　ａｎｄ（９－ＨａＰＯ４　ｉｎ　ｏｒｇａｎｉｃ　ｍｅｄｉｕｍ　ｆｏｌｌｏｗｅｄ　ｂｙ　ｃａｌｃｉｎａｔｉｏｎ　

ｉｎ　ｎ－ｂｕｔａｎｅ／ａｉｒ　ｅｎｖｉｒｏｎｍｅｎｔ　ａｔ　６７３　Ｋ．Ｔｈｅ　ｐｈｙｓｉｃｏ－ｃｈｅｍｉｃａｌ　ｐｒｏｐｅｒｔｉｅｓ　ａｎｄ　ｔｈｅ　ｃａｔａｌｙｔｉｃ　ｂｅｈａｖｉｏｒ　ｗｅｒｅ　ａｆｆｅｃｔｅｄ　ｂｙ　ｔｈｅ　ａｄｄｉｔｉｏｎ　ｏｆ　Ｃｒ　ａｎｄ　Ｃｏ　ｄｏｐａｎｔｓ．Ｈ２－ＴＰＲ　ｗａｓ　ｕｓｅｄ　ｔｏ　ｉｎｖｅｓｔｉｇａｔｅ　ｔｈｅ　ｎａｔｕｒｅ　ｏｆ　ｏｘｉｄａｎｔｓ　ｉｎ　ｔｈｅ　ｕｎｐｒｏｍｏｔｅｄ　ａｎｄ　ｐｒｏｍｏｔｅｄ　ｃａｔａｌｙｓｔｓ．Ｔｈｅ　ｒｅｓｕｌｔｓ　ｓｈｏｗｅｄ　ｔｈａｔ　ｂｏｔｈ　ｔｈｅ　Ｃｒ　ａｎｄ　Ｃｏ　ｐｒｏｍｏｔｅｒｓ　ｒｅｍａｒｋａｂｌｙ　ｌｏｗｅｒｅｄ　ｔｈｅ　ｔｅｍｐｅｒａｔｕｒｅ　ｏｆ　ｔｈｅ　ｒｅｄｕｃｔｉｏｎ　ｐｅａｋ　ａｓｓｏｃｉａｔｅｄ　ｗｉｔｈ　Ｖ５４－．Ｔｈｅ　ａｍｏｕｎｔ　ｏｆ　ｏｘｙｇｅｎ　

ｓｐｅｃｉｅｓ　ｏｒｉ百ｎａｔｅｄ　ｆｒｏｍ　ｔｈｅ　ａｃｔｉｖｅ　ｐｈａｓｅ，Ｖ４＋，ｒｅｍｏｖｅｄ　ｗａｓ　ｓｉｇｎｉｆｉｃａｎｔｌｙ　ｉｎｃｒｅａｓｅｄ　ｆｏｒ　Ｃｏ　ａｎｄ　Ｃｒ—ｐｒｏｍｏｔｅｄ　ｃａｔａｌｙｓｔｓ．Ｂｏｔｈ　Ｃｒ　ａｎｄ　Ｃｏ　ｄｏｐａｎｔｓ　ｉｍｐｒｏｖｅ　ｓｔｒｏｎｇｌｙ　ｔｈｅ佗一ｂｕｔａｎｅ　ｃｏｎｖｅｒｓｉｏｎ　ｗｉｔｈｏｕｔ　ｓａｃｒｉｆｉｃｉｎｇ　ｔｈｅ　ＭＡ　ｓｅｌｅｃｔｉｖｉｔｙ．Ａ　ｇｏｏｄ　ｃｏｒｒｅｌａｔｉｏｎ　ｗａｓ　ｏｂｓｅｒｖｅｄ　ｂｅｔｗｅｅｎ　ｔｈｅ　ａｍｏｕｎｔ　ｏｆ　ｏｘｙｇｅｎ　ｓｐｅｃｉｅｓ　ｒｅｍｏｖｅｄ　ｆｒｏｍ　Ｖ　＋　ｐｈａｓｅ　ａｎｄ　ｔｈｅ　ａｃｔｉｖｉｔｙ　ｆｏｒ　Ｔｔ—ｂｕｔａｎｅ　ｏｘｉｄａｔｉｏｎ　ｔｏ　ｍａｌｅｉｃ　ａｎｈｙｄｒｉｄｅ．Ｔｈｉｓ　ｓｕｇｇｅｓｔｅｄ　ｔｈａｔ　Ｖ４４－＿Ｏ　ｗａｓ　ｔｈｅ　ｃｅｎｔｅｒ　ｆｏｒ　ｔｈｅ　ａｃｔｉｖａｔｉｏｎ　ｏｆ佗一ｂｕｔａｎｅ．　Ｋｅｙ　ｗｏｒｄｓ：佗一ｂｕｔａｎｅ　ｏｘｉｄａｔｉｏｎ；ＶＰＯ：ｐｒｏｍｏｔｅｒ；ｍａｌｅｉｃ　ａｎｈｙｄｒｉｄｅ；ＴＰＲ　

１．Ｉｎｔｒｏｄｕｃｔｉｏｎ　Ｖａｎａｄｙｌ　ｐｙｒｏｐｈｏｓｐｈａｔｅ　ｃａｔａｌｙｓｔｓ　ａｒｅ　ｗｅｌｌ　ｋｎｏｗｎ　ａｓ　ｔｈｅ　ａｃｔｉｖｅ　ｐｈａｓｅ　ａｎｄ　ａｒｅ　ｃｏｍｍｅｒｃｉａｌｌｙ　ｕｓｅｄ　ｆｏｒ　ｔｈｅ　ｓｅｌｅｃｔｉｖｅ　ｏｘｉｄａｔｉｏｎ　ｏｆ　ｎ—ｂｕｔａｎｅ　ｔｏ　ｍａｌｅｉｃ　ａｎｈｙｄｒｉｄｅ　［】．１　Ｔｈｅ　ｃａｔａｌｙｔｉｃ　ｐｒｏｐｅｒｔｉｅｓ　ｏｆ　ｔｈｉｓ　ｃａｔａｌｙｓｔ　ｃｏｕｌｄ　ｂｅ　ｉｍｐｒｏｖｅｄ　ｂｙ　ｔｈｅ　ａｄｄｉｔｉｏｎ　ｏｆ　ｐｒｏｍｏｔｅｒｓ．Ｓｔｕｄｉｅｓ　ｂｙ　ｓｅｖｅｒａｌ　ｒｅｓｅａｒｃｈｅｒｓ　ｆ２－７１　ｓｈｏｗｅｄ　ｔｈａｔ　ＶＰＯ　ｃａｔａｌｙｓｔｓ　ｄｏｐｅｄ　ｗｉｔｈ　ｃｅｒｔａｉｎ　ｃａｔｉｏｎｓ　ｇａｖｅ　ｈｉｇｈｅｒ　ｓｅｌｅｃｔｉｖｉｔｙ　ｔｏ　ｍａｌｅｉｃ　ａｎｈｙｄｒｉｄｅ．Ａ　ｗｉｄｅ　ｓｐｅｃｔｒｕｍ　ｏｆ　ｃａｔｉｏｎｓ　ｈａｖｅ　ｂｅｅｎ　ｓｔｕｄｉｅｄ　ａｎｄ　ｒｅｐｏｒｔｅｄ　ｉｎ　ｂｏｔｈ　ｐａｔｅｎｔｓ　ａｎｄ　ｏｐｅｎ　ｌｉｔｅｒａｔｕｒｅ［８】ｓｕｃｈ　ａｓ　Ｃｏ，Ｃｄ，Ｚｎ，Ｂｉ，Ｌｉ，Ｎｉ，Ｃｒ，ｚｒ，　Ｍｇ，Ｆｅ　ａｎｄ　Ｔｉ．　Ｃｏｂａｌｔ　ａｎｄ　ｃｈｒｏｍｉｕｍ　ａｒｅ　ａｍｏｎｇ　ｔｈｅ　ｐｒｏｍｏｔｅｒ　ｅｌ—　ｅｍｅｎｔｓ　ａｆｆｅｃｔｉｎｇ　ｔｈｅ　ｃａｔａｌｙｔｉｃ　ｐｒｏｐｅｒｔｉｅｓ　ｏｆ　ｔｈｅ　ｂｕｌｋ　ｗｈｉｃｈ　ｈａｖｅ　ｂｅｅｎ　ｅｘａｍｉｎｅｄ　ｉｎ　ｄｅｔａｉｌ．Ｔｈｅ　ｅａｒｌｉｅｒ　ｗｏｒｋ　ｂｙ　Ｈｏｄｎｅｔ　ａｎｄ　Ｄｅｌｍｏｎ　ｆ９］９　ｃｏｎｃｌｕｄｅｄ　ｔｈａｔ　ｔｈｅ　ａｄｄｉ—　ｔｉｏｎ　ｏｆ　Ｃｏ　ａｔ　ｌｏｗｅｒ　ｌｅｖｅｌｓ　ｆＣｏ／Ｖ　ｕｐ　ｔｏ　０．０１５　ｉｎ　ａｔｏｍｉｃ　

ｒａｔｉｏ）ｉｎｃｒｅａｓｅｄ　ｔｈｅ　ｓｅｌｅｃｔｉｖｉｔｙ，ｗｈｉｌｅ　ｆｏｒ　ｔｈｅ　ａｄｄｉｔｉｏｎ　ａｔ　ｈｉｇｈｅｒ　ｌｅｖｅｌｓ　ｆＣｏ／Ｖ＝０．０１６—０．０５　ｉｎ　ａｔｏｍｉｃ　ｒａｔｉｏ１，　ｔｈｅ　ｅｘｃｅｓｓ　Ｃｏ　ｏｎ　ｔｈｅ　ｓｕｒｆａｃｅ　ｅｎｈａｎｃｅｄ　ｔｈｅ　ｆｏｒｍａｔｉｏｎ　ｏｆ　ＣＯ　ａｎｄ　ＣＯ２．Ｓａｊｉｐ　ｅｔ　ａ１．［１０】ｆｏｕｎｄ　ｔｈａｔ　ｔｈｅ　Ｃｏ　ｄｏｐａｎｔ（１％一５％）ｓｉｇｎｉｆｉｃａｎｔｌｙ　ｅｎｈａｎｃｅｄ　ｔｈｅ　ｓｅｌｅｃ—　ｔｉｖｉｔｙ　ａｎｄ　ｔｈｅ　ｉｎｔｒｉｎｓｉｃ　ａｃｔｉｖｉｔｙ　ｔｏ　ｍａｌｅｉｃ　ａｎｈｙｄｒｉｄｅ．　Ｐｉｅｒｉｎｉ　ｅｔ　ａ１．Ｉ　１１　ｌ　ｒｅｐｏｒｔｅｄ　ｔｈａｔ　ｔｈｅ　ａｃｔｉｖｉｔｙ　ａｎｄ　ｔｈｅ　ｓｅｌｅｃｔｉｖｉｔｙ　ｏｆ　ｔｈｅ　ＶＰＯ　ｃａｔａｌｙｓｔｓ　ｗｅｒｅ　ａｆｆｅｃｔｅｄ　ｂｙ　ｔｈｅ　ｉｎｃｏｒｐｏｒａｔｉｏｎ　ｏｆ　１％Ｃｒ　ｗｈｉｃｈ　ｗａｓ　ｐｒｅｐａｒｅｄ　ｂｙ　ｉｍ—　ｐｒｅｇｎａｔｉｏｎ　ｍｅｔｈｏｄ．Ｔｈｅ　ａｄｄｉｔｉｏｎ　ｏｆ　Ｃｒ　ｙｉｅｌｄｓ　ｃａｔａ—　ｌｙｓｔｓ　ｗｉｔｈ　ｃａ．５０％ｈｉｇｈｅｒ　ｓｕｒｆａｃｅ　ａｒｅａ　ｔｈａｎ　ｔｈｅ　ａｎ—　ｐｒｏｍｏｔｅｄ　ＶＰＯ．Ｔｈｅｙ　ａｌｓｏ　ｆｏｕｎｄ　ｔｈａｔ　ｔｈｅｒｅ　ｗａｓ　ｎｏ　ｃｏｒｒｅｌａｔｉｏｎ　ｂｅｔｗｅｅｎ　ｓｕｒｆａｃｅ　ａｒｅａ　ａｎｄ　Ｃｒ　ｌｏａｄ．Ｔｈｅ　ｐｏｔｅｎｔｉａｌ　ｏｆ　Ｃｒ　ａｎｄ　Ｃｏ　ｉｎ　ｉｍｐｒｏｖｉｎｇ　ｔｈｅ　ｃａｔａｌｙｔｉｃ　ｐｅｒ—　ｆｏｒｍａｎｃｅ　ｏｆ　ＶＰＯ　ｃａｔａｌｙｓｔｓ　ｉｎ　ｒｅｌａｔｉｏｎｓｈｉｐｓ　ｔｏ　ｔｈｅ　ｍｏ－　ｂｉｌｉｔｙ，ｒｅａｃｔｉｖｉｔｙ，ａｎｄ　ｏｒｉｇｉｎ　ｏｆ　ｔｈｅ　ｌａｔｔｉｃｅ　ｏｘｙｇｅｎ　ａｒｅ　ｉｎｖｅｓｔｉｇａｔｅｄ　ｉｎ　ｔｈｉｓ　ｓｔｕｄｙ．　

Ｃｏｒｒｅｓｐｏｎｄｉｎｇ　ａｕｔｈｏｒ．Ｔｅｌ：＋６Ｏ３＿８９４６　６８０９；Ｆａｘ：＋６０３－８９４６　６７５８；Ｅ－ｍａｉｌ：ｙａｐ＠ｆｓａｓ．ｕｐｍ．ｅｄｕ．ｍｙ　

一　维普资讯 http://www.cqvip.com ２．Ｅｘｐｅｒｉｍｅｎｔａｌ　２．１．Ｓｙｎｔｈｅｓｉｓ　ｏｆ　ｃａｔａｌｙｓｔｓ　

Ｊｏｕｒｎａｌ　ｏｆ　Ｎａｔｕｒａｌ　Ｇａｓ　Ｃｈｅｍｉｓｔｒｙ　Ｖｏ１．１５　Ｎｏ．２　２００６　

Ｔｈｅ　ｖａｎａｄｉｕｍ　ｐｈｏｓｐｈｏｒｕｓ　ｏｘｉｄｅ　ｐｒｅｃｕｒｓｏｒｓ　ｗｅｒｅ　ｐｒｅｐａｒｅｄ　ｖｉａ　ｏｒｇａｎｉｃ　ｒｏｕｔｅ　ｂｙ　ｔｈｅ　ｒｅａｃｔｉｏｎ　ｏｆ　Ｖ２Ｏ５　（２Ｏ．Ｏ　ｇ１　ｗｉｔｈ　ｉｓｏｂｕｔａｎｏ１（１２０　ｍ１）ｉｎ　ｔｈｅ　ｓｏｌｖｅｎｔ　ｏｆ　ｂｅｎ—　ｚｙｌ　ａｌｃｏｈｏｌ　ｆ８０　ｍｌ１．Ｏｎｅ　ｐｅｒｃｅｎｔ　ｏｆ　Ｃｒ　ｏｒ　Ｃｏ　ｐｒｏｍｏｔｅｒ　ｗａｓ　ａｄｄｅｄ　ａｓ　Ｃｒ（ＮＯ３）３・９Ｈ２０　ｏｒ　Ｃｏ（ＮＯ３）２・６Ｈ２０　ｉｎｔｏ　ｔｈｅ　ｒｅａｃｔｉｏｎ　ｍｉｘｔｕｒｅ　ｆｏｒ　Ｃｒ　ａｎｄ　Ｃｏ　ｐｒｏｍｏｔｅｄ　ｐｒｅ—　ｃｕｒｓｏｒｓ．Ａｆｔｅｒ　ｔｈｅ　ｒｅａｃｔｉｏｎ　ｍｉｘｔｕｒｅ　ｗａｓ　ｒｅｆｌｕｘｅｄ　ｆｏｒ　７　ｈ　ａｔ　３９３　Ｋ，ｔｈｅ　ｍｉｘｔｕｒｅ　ｗａｓ　ｃｏｏｌｅｄ　ｔｏ　ｒｏｏｍ　ｔｅｍｐｅｒ－　ａｔｕｒｅ　ａｎｄ　ｗａｓ　ｌｅｆｔ　ｓｔｉｒｒｉｎｇ　ｏｖｅｒｎｉｇｈｔ．Ｔｈｅｎ　２５．３８　ｍｌ　ｏｆ　ｏ－Ｈ３ＰＯ４（８５％１　ｗａｓ　ａｄｄｅｄ　ｔｏ　ｏｂｔａｉｎ　ｔｈｅ　ｄｅｓｉｒｅｄ　Ｐ：Ｖ　ａｔｏｍｉｃ　ｒａｔｉｏ　ｏｆ　１．０．Ｔｈｅ　ｍｉｘｔｕｒｅ　ｗａｓ　ｆｕｒｔｈｅｒ　ｒｅｆｌｕｘｅｄ　ｆｏｒ　ａｎｏｔｈｅｒ　３　ｈ　ａｔ　３９３　Ｋ　ｗｉｔｈ　ｓｔｉｒｒｉｎｇ．Ｔｈｅ　ｏｂｔａｉｎｅｄ　ｂｌｕｅ　ｓｌｕｒｒｙ　ｗａｓ　ｃｏｏｌｅｄ　ｔｏ　ｒｏｏｍ　ｔｅｍｐｅｒａｔｕｒｅ　ａｎｄ　ｔｈｅ　ｓｏｌｉｄ　ｗａｓ　ｒｅｃｏｖｅｒｅｄ　ｂｙ　ａ　ｃｅｎｔｒｉｆｕｇｅ．Ｔｈｅ　ｓｏｌｉｄ　ｗａｓ　ｗａｓｈｅｄ　ｓｐａｒｉｎｇｌｙ　ｗｉｔｈ　ｗａｔｅｒ　ａｎｄ　ｄｒｉｅｄ　ｉｎ　ａｉｒ　ａｔ　３７３　Ｋ　ｆｏｒ　２４　ｈ。　Ｔｈｅ　ｕｎｐｒｏｍｏｔｅｄ．Ｃｒ　ａｎｄ　Ｃｏ　ｐｒｏｍｏｔｅｄ　ｐｒｅｃｕｒ－　ｓｏｒｓ，ＶＯＨＰＯ４・０．５Ｈ２Ｏ　ｗｅｒｅ　ａｃｔｉｖａｔｅｄ　ｉｎ　ａ　ｒｅａｃｔｉｏｎ　ｆｌｏｗ　ｏｆ　ｎ—ｂｕｔａｎｅ／ａｉｒ　ｍｉｘｔｕｒｅ（Ｏ．７５％ｎ－ｂｕｔａｎｅ　ｉｎ　ａｉｒ）　ａｔ　６７３　Ｋ　ｆｏｒ　６　ｈ．Ｔｈｅ　ｏｂｔａｉｎｅｄ　ｃａｔａｌｙｓｔｓ　ｗｅｒｅ　ｄｅｎｏｔｅｄ　ａｓ　ＶＰＯ，ＶＰＯＣｒ　ａｎｄ　ＶＰＯＣｏ，ｒｅｓｐｅｃｔｉｖｅｌｙ．　