Adsorption and Reaction of CO on (100) Surface of SrTiO3 by Density Function Theory Calcula

合集下载

ZrO_2在Si_100_2_1表面原子层淀积反应机理的密度泛函理论研究

2006年第64卷化学学报V ol. 64, 2006第11期, 1133～1139 ACTA CHIMICA SINICA No. 11, 1133～1139* E-mail: dwzhang@Received October 17, 2005; revised December 1, 2005; accepted February 14, 2006.1134化学学报V ol. 64, 2006料, 能够在保持和增大栅极电容的同时, 使介质层仍保持足够的物理厚度来限制隧穿效应的影响.以IVB族元素氧化物HfO2和ZrO2为代表的高k栅介质, 因其热稳定性好, 介电常数高, 被认为最有潜力成为下一代高k栅介质材料[6～11]. 目前, 像ZrO2 和HfO2这样的高k栅介质薄膜已经成功地由原子层气相淀积(ALD)、金属有机化学气相淀积(MOCVD)和物理气相淀积(PVD)技术制备. 其中, ALD被认为是淀积高k栅介质的一个最重要的技术[12,13].ALD技术的原理是基于在衬底表面交替的饱和反应, 每一个前体反应物交替、独立地进入反应腔, 它们之间不发生直接反应, 而是和吸附在衬底表面的已经反应的前体反应物进行反应. 由于 ALD表面反应是自限制反应, 即利用自身控制的化学反应进行淀积, 当衬底表面的反应物达到饱和时, 就不再进行反应, 增长自行中止. 这样就可以通过脉冲的次数在原子级水平精确控制薄膜的厚度. 所以使用ALD生长的薄膜, 具有良好的保持性, 一致性, 可重复和数字化精确控制性等优点[14～20].目前, 高k栅介质要完全取代传统的SiO2栅介质需要克服许多困难. 因为SiO2不仅和Si之间的界面近乎完美, 而且具有优异的机械、电学、介电和化学稳定性. 同时, 人们对SiO2和Si界面间的理论模型和各种反应机理也有了比较系统、全面和深入的研究. 而对于高k 栅介质的研究才刚刚起步, 面临很大的困难和挑战.最近几年, 高k栅介质ZrO2 ALD反应机理的量子化学研究已有报道, 例如, Widjaja和Musgrave[21]在B3LYP计算水平, 使用Zr-[O-Zr(OH)3]3-OH和Zr-[O- Zr(OH)3]3-Cl等簇来模拟 ZrO2表面, 研究了前体反应物ZrCl4和H2O在ZrO2表面的反应路径以及各个驻点的几何结构, 并且提出了ZrO2 ALD初始反应的反应机理. 另外, Widjaja等[22]也研究了单羟基和裸Si表面ZrO2 ALD的反应机理, 重点比较了前体反应物在Si—H*和Si—OH*, Zr—Cl*和Si—Cl*活性位的反应(星号表示表面活性基团). 最近, 我们[23]研究了ZrO2在Ge/Si(100)- 2×1表面的ALD的反应机理, 讨论了前体反应物在不同的Si1－x Ge x表面的反应路径, 以及相应的能量和结构的变化. 虽然关于ZrO2 ALD反应机理已经得到了不同侧面的研究, 然而, ALD过程中许多热力学和动力学问题还需要进一步研究. 例如, 实验发现裸Si表面的羟基化使ALD变得容易进行, 相邻羟基对反应的影响的理论研究却很少有报道. 在本文的研究中, 重点比较单羟基和双羟基Si表面反应, 考察相邻羟基对反应能量和结构的影响. 另外, 前面提到的研究中前体反应物ZrCl4和H2O在Si和SiO2表面反应势能面的计算完全基于各个驻点独立的优化结构. 在本研究中, 将在小的计算模型(SiH3—OH)中引入内禀反应坐标(IRC)方法[24]正确描述从化学吸附态到最终产物的连续最速降反应路径, 并且确定过渡态是否是正确的反应过渡态, 最后与Si9簇模型的计算结果进行了对比. 考虑到 ZrCl4化学吸附能对基组的敏感[22], 在本文的研究中, 对参与表面反应的活性原子, 在计算能力允许的情况下, 采用了比文献[22]相对更高级的基组, 来保证计算得到更加准确的能量值.使用ZrCl4和H2O作为前体反应物ALD ZrO2, 初始反应可以分为两个连续的半反应. 如Scheme 1所示, ZrCl4的半反应, 包括单羟基Si表面的反应I, 双羟基Si 表面的反应III和IV, 表示ZrCl4和Si表面的—OH的反应; H2O的半反应, 包括单羟基Si表面的反应II, 双羟基Si表面的反应V和VI, 表示H2O与I, IV和V得到的锆化物表面活性位的反应.图式1Scheme 11 计算模型与方法以前的计算中[22,25～27], Si9H12簇(图1)常常被用来作为模拟Si(100)-2×1表面的化学反应和振动性质. Si9簇由四层Si原子组成, 其中第一层两个表面Si原子, 第二层四个Si原子, 第三层两个Si原子, 第四层一个Si原子. 不饱和的Si原子用H原子饱和, 目的是阻止未配对电子的转移. 本研究中, 使用单羟基和双羟基化的Si9H13OH和Si9H12(OH)2簇模型. 另外, 在保证ZrO2 ALD反应的基本特征前体下, SiH3-OH小分子模型被用来代替SiNo. 11任杰等：ZrO 2在Si(100)-2×1表面原子层淀积反应机理的密度泛函理论研究1135算速度.图1 Si 9H 12簇Si 原子为灰色的大球, H 原子为浅灰色的小球Figure 1 Si 9H 12 one-dimer clusterSi atoms are grey and H atoms are light grey全部计算由Gaussian 03程序[28]完成, 采用B3LYP 计算方法[29,30], 混合基组方式. Zr 的价电子层基组采用LANL2DZ 基函数, 内层电子同样采用LANL2DZ 有效核势来加快计算速度. 第一层表面Si —Si, —OH 和—H 表面活性原子, 以及H 2O 和Cl 原子采用较高级的基函数6-31＋G(d), 2～4层Si 以及用于饱和的H 原子使用6-31G 基函数, 几何结构采用全部优化方法, 不做任何限制. 在优化结构的基础上做频率分析计算, 来验证各个驻点在反应势能面上的性质. 保证计算得到的局部极小点所有频率为正值, 过渡态只有一个虚频. 另外, 计算得到能量值都经过零点能修正.2 结果和讨论2.1 ZrCl 4在Si(100)-2×1表面的半反应I, III 和IVZrCl 4半反应I, III 和IV 的反应路径和能级如图2所示, 其中在单羟基Si 9H 13-OH 表面反应用虚线所示, 双羟基Si 9H 12-(OH)2用实线所示, 相应的焓值(ΔH 298)见表1和图2. ZrCl 4首先吸附在一个Si —OH*活性位, 形成一个稳定的络合物ZrCl 4 (a), 化学吸附能分别为－58.4 (b')和－100.6 (b) kJ/mol. Widjaja 和Musgrave [21]已经建议这个络合物的形成是由于表面羟基O 原子的 2p 孤对电子和空的Zr 原子d 轨道作用的结果. 可以预见, 双羟基Si 基表面反应, 相邻的—OH 的O 原子的孤对电子对Zr 原子空的d 轨道作用, 是其化学吸附能增加的主要原因. 随后反应经过一个四元环结构过渡态(TS). 相对于ZrCl 4 (a), 活化能分别为58.3 (c')和53.0 (c) kJ/mol. 可以看到, 相邻—OH 对活化势垒高度的影响却很小. 然后, ZrCl 4中的一个Cl 原子和—OH 的H 原子重新组合形成 HCl 分子, 最后解吸附. 这里需要指出的是, 对于半反应III, 由于相邻—OH 的存在, HCl 分子存在一个弱的物理吸附态HCl (a), 其能量仅仅比最后产物的总能量低 4.1 kJ/mol. 而对于半反应 I, 计算发现, 物理吸附态HCl (a)的能量相对于反应产物能量高, 不能稳定地存在于反应过程中. 而半反应IV, 可以看作 III 的后续反应, —O —ZrCl 3与相邻的—OH 作用, 经过一个66.4 kJ/mol 的势垒, 然后脱去一个HCl, 形成最后产物. 值得注意的是, 对于半反应IV, 这是一个吸热反应, 吸热64.5 kJ/mol.图2 298 K ZrCl 4在Si 9H 13-OH (虚线)和Si 9H 12-(OH)2 (实线)表面反应的反应路径和能级变化图(所示能量是和反应物总能量的能量差, 结构用Si 9H 12-(OH)2表示)Figure 2 Reaction path and predicted energetics for reactions of ZrCl 4 on the Si 9H 13-OH (dashed) and Si 9H 12-(OH)2 (solid) surface sites at 298 K (Energies are relative to the sum of the reactants energies. The structures are shown using Si 9H 12-(OH)2 cluster)从表1和图2可以看出, 无论前体反应物ZrCl 4在单羟基还是双羟基Si 表面反应, 最初的半反应I 和III 都是放热反应, 分别为－36.0 (e')和－65.8 (e) kJ/mol. 对于双羟基Si 表面反应, 过渡态TS-1的能级远远低于反应物总能级, 所以经过羟基化处理的Si 基表面, 从能量上看是非常有利于初始反应向生成产物的方向进行的. 从图2可以看到无论单羟基还是双羟基Si 表面的反应, 都要经历一个吸附中间体的反应路径, 所以说从机理上两者也没有区别.另外, 反应路径上关键键长和原子间距的变化也描绘了表面反应的特点, 从表2可以看到半反应I 和III 中, 吸附络合物ZrCl 4 (a), O —H 的键长分别是0.097 (b')和0.098 (b) nm, Zr —Cl 的键长是0.241 (b')和0.246 (b) nm, 而在TS 结构中, O —H 的键长增长为0.134 (c')和0.1381136化学学报V ol. 64, 2006表1 298 K ZrCl4和H2O半反应的吸附和解离反应焓(ΔH298) (kJ/mol)的比较(能量是和反应物总能量的能量差)Table 1Comparison of reaction enthalpies (ΔH298) (in unit kJ/mol) calculated for the ZrCl4 and H2O half-reactions at 298 K (Energiesare relative to the sum of the reactants energies)Reaction Chemisorptionstate a Transition state Physisorption state a Product aI －58.4 －0.1 —－36.0II －56.9 20.7 2.86.3III －100.6 －47.6 －69.9 －65.8IV — 66.4 62.064.5V －63.8 22.1 6.712.7VI －60.7 19.6 6.916.3a Chemisorption state including ZrCl4(a) and H2O (a), physisorption state including HCl (a) and product including —O—ZrCl3, —O—ZrCl2—O— and—O—Zr(OH)Cl—O— complexs in Figures 2 and 3.表2 反应路径各个驻点上一些代表性键长(nm) (半反应I, III和IV的O是Si—OH的O, II, V和VI的O是反应前体H2O的O, Cl是最后形成HCl分子的Cl)Table 2 Representative bond lengths (in unit nm) for the structures of stationary points on potential energy surface (O denotes the Oatom of Si—OH in reactions I, III and IV, and the O atom of H2O in reaction II, V and VI; Cl denotes the Cl atom forming HCl product) ReactantChemisorptionstate a Transitionstate Product a Reaction I III IV I III IV I IIIIV I III IVStationary point a a e b' b c' c f e' e h Zr—O 0.2350.2370.2060.2120.208 0.191 0.1960.195O—H 0.0970.0970.097 0.0970.098 0.1340.1380.139Zr—Cl 0.2340.2340.234 0.241 0.246 0.2880.2910.289Reaction II V VI II V VI II V VI II V VIStationarypointa a e b'b b" c'c c" e' e e"Zr—O 0.2410.2420.2410.207 0.2090.210 0.192 0.1940.195O—H 0.0970.0970.0970.0970.0970.0970.136 0.1350.131Zr—Cl 0.2370.2390.241 0.242 0.2430.2450.295 0.3100.323a Chemisorption state including ZrCl4(a) and H2O (a) and product including —O—ZrCl3, —O—ZrCl2—O— and —O—Zr(OH)Cl—O— complexes in Figures 2 and 3.(c) nm, Zr—Cl键增长为0.288 (c')和0.291 (c) nm, 最后O—H和Zr—Cl键断裂形成产物. 对于Zr—O键, 吸附络合物的键长是0.235 (b')和0.237 (b) nm, TS的键长减少为0.206 (c')和0.212 (c) nm, 最后的产物, 键长分别是0.191 (e')和0.196 (e) nm, Zr—O键最终形成.2.2 H2O在Si(100)-2×1表面半反应II, V和VI如表1所示, 半反应VI的能级与II和V的能级非常接近, 图3为了简单清晰, 省略了半反应VI的反应路径和能级图, 只画出了H2O在Si(100)-2×1表面半反应II和V的反应路径和能级图. 同样, 图中虚线表示单羟基Si表面反应, 实线表示双羟基Si表面反应. 半反应II和V的活性表面分别是I和IV的产物, 活性基团分别为—O—ZrCl3和—O—ZrCl2—O—. 同样, 半反应VI的反应表面是也是V的产物, 表示为—O—Zr(OH)Cl— O—. H2O首先吸附在表面活性基团形成一个稳定的吸附络合物, 化学吸附能分别为－56.9 (b'), －63.8 (b)和－60.7 (b") kJ/mol (半反应VI的标示参考表2), 这个络合物的形成机理与ZrCl4半反应中ZrCl4在Si—OH*活性Zr的空的d轨道的作用的结果. 同样, 经过一个与ZrCl4半反应相似的四元环过渡态. 相对于化学吸附态H2O (a), 活化能分别为77.6 (c'), 85.9 (c)和80.3 (c") kJ/mol, 然后经过一个弱的物理吸附态的HCl (a), HCl产物分子解吸附. 从表1和图3可以看出, H2O半反应(II, V和VI)都是弱的吸热反应, 分别为6.3 (e'), 12.7 (e)和16.3 (e") kJ/mol, 而且过渡态的能级都要稍高于反应物总能级. 从能量上看, 不利于反应向生成产物的方向进行. 另外, 半反应II, V和VI中相对应的各个驻点的能量差很小, 在2.5～10.0 kJ/mol之间, 这与ZrCl4半反应存在明显的不同. 可以理解为, 前体反应物H2O的吸附和解离反应并没有受到—O—ZrCl2—O—(h) (图2)和—O—Zr(OH)- Cl—O—(e) (图3)活性位中相邻—O—和—OH基团的影响.同时, 反应路径上的相关键的变化也显示了H2O半反应的特征, 对于吸附络合物H2O (a), O—H的键长分别是0.097 (b'), 0.097 (b)和0.097 (b") nm, Zr—Cl的键长分别是0.242 (b'), 0.243 (b)和0.245 (b") nm (表2); 而TS结构, O—H增长为0.136 (c'), 0.135 (c)和0.131 (c")No. 11 任杰等：ZrO2在Si(100)-2×1表面原子层淀积反应机理的密度泛函理论研究1137图3 298 K H2O在Si9H13-OH (虚线)和Si9H12-(OH)2(实线) 表面反应的反应路径和能级变化图(所示能量是和反应物总能量的能量差, 结构用Si9H12-(OH)2表示)Figure 3Reaction path and predicted energetics for reactions of H2O on the Si9H13-OH (dashed) and Si9H12-(OH)2 (solid) surface sites at 298 K (Energies are relative to the sum of the reactants energies. The structures are shown using Si9H12-(OH)2 cluster)nm, Zr—Cl增长为0.295 (c'), 0.310 (c)和0.323 (c") nm, 最后O—H和Zr—Cl键的断裂, 形成产物. 而对于Zr—O 键, 吸附络合物的键长是0.241 (b'), 0.241 (b)和0.242 (b") nm, TS的键长是0.207 (c'), 0.209 (c)和0.210 (c") nm, 产物的键长是0.192 (e'), 0.194 (e) 0.195 (e") nm, 最后Zr—O键完全形成.2.3 沿着IRC路径相关键长和原子间距的变化IRC通常被用来评价过渡态是不是真正的反应过渡态, 是不是正确连接反应物和产物的过渡态[31]. 由于IRC在计算上是一个非常耗时的计算方法, 如果直接用在Si9簇的表面反应上, 从计算能力上考虑不可行. 所以在本研究中取相对较小的SiH3-OH计算模型, 通过描述SiH3-OH-ZrCl4和SiH3-O-ZrCl3-H2O吸附配合物的HCl的消去反应, 来考察ZrCl4和H2O半反应的反应路径. 考虑到小的模型可能影响到最后得到正确的结论, 所以我们把计算得到的SiH3-OH和Si9H13-OH表面反应的过渡态结构进行了比较. 结果发现 SiH3-OH- 结构: 对应的Zr—O, Zr—Cl, Cl—H, O—H距离(nm)为: 0.206(S)/0.206(L), 0.285(S)/0.288(L), 0.148(S)/0.147(L), 0.133(S)/0.144(L); 对应的四元环内∠Zr—O—H, ∠O—Zr—Cl, ∠Zr—Cl—H, ∠Cl—H—O (°)为: 90.8(S)/90.1(L), 63.9(S)/63.9(L), 60.3(S)/58.9(L), 145.0(S)/147.0(L). 另外, 无论SiH3-OH-ZrCl4还是Si9H13-OH-ZrCl4过渡态, 虚频的主要振动模式都显示是O—H的伸缩振动. 因此, 我们认为SiH3-OH模型取得还是合理的, 用来模拟Si9H13-OH簇表面反应的反应路径是可行的. 值得指出的是, 最近Han等[32]用Si(OH3)-OH小分子模型模拟SiO2表面也取得了理想的计算结果.IRC计算的最低能量路径取的是质量权重内坐标, 最小步长为0.05 (amu)1/2•bohr. 沿着 SiH3-OH-ZrCl4吸附络合物的HCl的消除反应IRC路径, 和过渡态四元环结构紧密相关的几个键长和原子间距的变化如图4所示. 质量权重坐标用S表示, 其中过渡态位于S＝0 (amu)1/2•bohr处. 可以看到, 随着反应的进行, Zr—Cl和O—H键长是慢慢增加, 同时Zr—O键长慢慢缩短并且Cl—H距离逐渐靠近, 慢慢成键. 很明显, Zr—Cl和Zr—O键长的变化要比O—H和Cl—H距离的变化要小很多, 这是因为O—H和Cl—H涉及到键的断裂和生成. 从图4可以看到, 在S＝－1.0 (amu)1/2•bohr后, O—H键从逐渐增长到突然增加很快, 同时Cl—H的距离也突然缩短, 一直到键的形成. 图4也显示了键的形成和断裂主要在过渡态结构以后完成.图4沿着SiH3-OH-ZrCl4络合物的HCl消除反应的IRC路径的相关键长和原子距离(Zr—O, Zr—Cl, Cl—H和O—H)的变化左边是前体反应物的化学吸附态, 右边是产物HCl和SiH3-O-ZrCl3, 过渡态在S＝0 amu1/2•bohr处Figure 4Plot of the changes in selected bond lengths and dis-tances (Zr—O, Zr—Cl, Cl—H and O—H) along the calculated IRC for the elimination of HCl from SiH3-OH-ZrCl4 complexZrCl4 (a) chemisorbed complex is on the left; products, i.e., HCl and SiH3-O-ZrCl3 are on the right, and the TS is set to S＝0 [(amu)1/2•bohr]1138化学学报 V ol. 64, 2006同样, 我们考察了SiH 3-O-ZrCl 3-H 2O 的HCl 消除反应的IRC 路径上相关键的变化, 得到的键长和原子间距随 IRC 路径的变化图和图4非常相似, 由于篇幅所限没有列出. 这从一个侧面反映了ZrO 2 ALD 的基本特征, 即前体反应物ZrCl 4和H 2O 的半反应是交替进行的, 前一个半反应得到的产物提供活性表面给后一个半反应, 两半反应经历了一个相似的四元环过渡态结构和反应机理. 2.4 温度效应表3列出了半反应I ～VI 在298, 400和600 K 时的吉布斯自由能值(ΔG ). 由于IV 没有化学吸附态, VI 与V 能量非常相近, 为了简化, 表3只列入I ～III 和V 的自由能值作为单、双羟基Si 表面反应温度效应的比较. 可以看到, 相对于反应物和产物, 吸附络合物和过渡态的自由能随着温度的增加而增加, 结果导致络合物变得不稳定. 因此, 在实验中剩余的反应物和副产物可能通过增加温度而解吸附除去, 这一现象已经得到了验证[13,33]. 对于半反应I 和III, 总的自由能变化是负值, 说明整个半反应是自发的. 而对于半反应II, V, 总的自由能变化是正值, 意味着H 2O 的半反应不是自发的. 值得注意的是, 温度从298到600 K, 产物的总的自由能变化不是很明显, 只是对吸附中间体和活化势垒有明显的影响. 其中, ZrCl 4的半反应变化明显, 而H 2O 的半反应不是很明显. 从298到600 K 产物的最大自由能差, I, III, IV 分别为－5.6, 8.5, －38.5 kJ/mol, II, V, VI 分别为－1.6, －0.4, －0.8 kJ/mol. 这说明增加温度, 对H 2O 半反应影响不是很大, 而对于ZrCl 4半反应, 特别是IV 半反应有明显的影响.在一个高的温度, 吸附络合物向反应物方向的解吸附活化自由能明显比向产物方向的解离自由能要低, 提高表面反应温度, 吸附分子的解吸附将变得更容易, 而解离将变得更困难. 所以在实际ZrO 2 ALD 过程中, 将尽量保持合适的温度, 温度太低反应速度可能受到限制, 而过高会增加前体反应物的解吸附. 另外, 还需要保持一定的高压力, 增加反应物的浓度, 来降低前体反应物的解吸附对反应的影响. 总之, 在实验中通过控制反应条件, 如脉冲时间, 腔体压力和反应温度, 可以使薄膜达到最大的生成速度和最好的质量.3 结论从理论上研究了在经过羟基预处理的Si(100)-2×1表面ZrO 2 ALD 的初始反应机理. 由于Zr 的空的d 轨道和接近的O 的2p 孤对电子的强烈作用, ZrCl 4和H 2O 可以直接吸附在表面活性位形成稳定的化学吸附态, ZrCl 4和H 2O 半反应都经历了相似的吸附中间体反应路径. 同样, IRC 研究也证实了ZrCl 4和H 2O 半反应具有相似的过渡态结构和反应路径. 通过对单、双羟基Si 簇模型反应势能面上各个驻点的能量比较, 发现相邻—OH 对ZrCl 4半反应有较明显的影响, 特别是对ZrCl 4化学吸附能的影响比较大, 而对H 2O 半反应, —O —ZrCl 2—O —和—O —Zr(OH)Cl —O —活性位中相邻—O —和—OH 基团的影响不明显. 另外, 我们也发现随着温度的增加, 吸附络合物的稳定性也随之降低, 这样的结果就使吸附络合物向反应物方向的解吸附将变得更容易, 而向产物方向的解离将变得更困难.表3 不同温度(K)下ZrCl 4和H 2O 在Si 9H 13-OH 和Si 9H 12-(OH)2表面吸附和解离反应的吉布斯自由能值a (kJ/mol)(能量都是和反应物总吉布斯自由能的能量差)Table 3 Predicted Gibbs free energies a (in unit kJ/mol) for the adsorption and decomposition of ZrCl 4 and H 2O on Si 9H 13-OH and Si 9H 12-(OH)2 surface at different temperatures (K) (Energies are relative to the sum of the reactants energies)Chemisorption stateb Transition statePhysisorption state b Product bReaction I III I III I III I III ΔG 298 －17.2 －46.4 42.8 10.3 －24.7 －40.5－56.8ΔG 400－3.3－28.1 57.4 30.1－9.4 －42.2－53.8ΔG 600 22.8 7.0 85.3 68.5 20.1 －46.1－48.3Reaction II V II V II V II V ΔG 298 －15.3 －22.7 65.6 63.6 36.7 39.5 5.8 13.3ΔG 400－1.2－8.8 81.0 77.748.150.5 5.4 13.3ΔG 600 25.6 17.6 110.6 105.0 69.3 71.1 4.2 12.9aIncluding zero-point energy corrections. b Chemisorption state including ZrCl 4 (a) and H 2O (a), physisorption state including HCl (a) and product including —O —ZrCl 3, —O —ZrCl 2—O — and —O —Zr(OH)Cl —O — complexes in Figures 2 and 3.No. 11 任杰等：ZrO2在Si(100)-2×1表面原子层淀积反应机理的密度泛函理论研究1139References1 Muller, D. A.; Sorsch, T.; Moccio, S.; Baumann, F. H.; Ev-ans-Lutterodt, K.; Timp, G. Nature1999, 399, 758.2 Packan, P. A. Science1999, 285, 2079.3 Gusev, E. P.; Cabral, C., Jr.; Copel, M.; D’Emic, C.; Gribe-lyuk, M. Microelectron. Eng. 2003, 69, 145.4 Green, M. L.; Gusev, E. P.; Degraeve, R.; Garfunkel, E. L.J. Appl. Phys. 2001, 90, 2057.5 Wilk, G. D.; Wallace, R. M.; Anthony, J. M. J. Appl. Phys.2001, 89, 5243.6 Ngai, T.; Qi, W. J.; Sharma, R.; Fretwell, J. L.; Chen, X.;Lee, J. C.; Banerjee, S. K. Appl. Phys. Lett. 2001, 78, 3085.7 Ngai, T.; Qi, W. J.; Sharma, R.; Fretwell, J. L.; Chen, X.;Lee, J. C.; Banerjee, S. K. Appl. Phys. Lett. 2000, 76, 502.8 Copel, M.; Gribelyuk, M.; Gusev, E. Appl. Phys. Lett. 2000,76, 436.9 Wang, S. J.; Ong, C. K.; Xu, S. Y.; Chen, P.; Tiju, W. C.;Chai, J. W.; Huan, A. C. H.; Yoo, W. J.; Lim, J. S.; Feng, W.; Choi, W. K. Appl. Phys. Lett. 2001, 78, 1604.10 Qi, W.-J.; Nieh, R.; Lee, B. H.; Kang, L.; Jeon, Y.; Lee, J.C. Appl. Phys. Lett. 2000, 77, 3269.11 Lee, J. Y.; Lai, B. C. In Handbook of Thin Film Materials,Vol. 3, Ed.: Nalwa, H. S., Academic Press, San Diego, 2002, p. 53.12 Kukli, K.; Ritala, M.; Aarik, J.; Uustare, T.; Leskelä, M. J.Appl. Phys. 2002, 92, 1833.13 George, S. M.; Ott, A. W.; Klaus, J. W. J. Phys. Chem.1996, 100, 13121.14 Leskelä, M.; Ritala, M. Thin Solid Films2002, 409, 138.15 Ritala, M.; Leskelä, M. In Handbook of Thin Film Materi-als, Vol. 1, Ed.: Nalwa, H. S., Academic Press, San Diego, 2002, p. 103.16 Leskelä, M.; Ritala, M. Angew. Chem., Int. Ed. 2003, 42,5548.17 Suntola, T. Thin Solid Films1992, 216, 84.18 Leskelä, M.; Ritala, M. Nanotechnology1999, 10, 19.19 Kim, H. J. Vac. Sci. Technol., B 2003, 21, 2231.20 Crowell, J. E. J. Vac. Sci. Technol., A 2003, 21, S88.21 Widjaja, Y.; Musgrave, C. B. Appl. Phys. Lett. 2002, 81,304.22 Widjaja, Y.; Han, J. H.; Musgrave, C. B. J. Phys. Chem. B2003, 107, 9319.23 Chen, W.; Zhang, D.-W.; Ren, J.; Lu, H.-L.; Zhang, J.-Y.;Xu, M.; Wang, J.-T.; Wang, L.-K. Thin Solid Films 2005, 479, 73.24 Gonzalez, C.; Schlegel, H. B. J. Chem. Phys. 1989, 90,2154.25 Jeloaica, L.; Estève, A.; Djafari Rouhani, M.; Estève, D.Appl. Phys. Lett. 2003, 83, 542.26 Estève, A.; Djafari Rouhani, M.; Jeloaica, L.; Estève, D.Comput. Mater. Sci. 2003, 27, 75.27 Kang, J. K.; Musgrave, C. B. J. Appl. Phys. 2002, 91, 3408.28 Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G.E.; Robb, M. A.; Cheeseman, J. R.; Zakrzewski, V. G.;Montgomery, J. A. Jr.; Stratmann, R. E.; Burant, J. C.;Dapprich, S.; Millam, J. M.; Daniels, A. D.; Kudin, K. N.;Strain, M. C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.;Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghava-chari, K.; Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Ste-fanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Ko-maromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J.; Keith, T.; AlLaham, M. A.; Peng, C. Y.; Nanayakkara, A.; Gon-zalez, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.;Chen, W.; Wong, M. W.; Andres, J. L.; Gonzalez, C.;HeadGordon, M.; Replogle, E. S.; Pople, J. A. Gaussian 03, Gaussian, Inc., Pittsburgh PA, 2003.29 Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B1988, 37, 785.30 Becke, A. D. J. Chem. Phys. 1993, 98, 5648.31 Wang, W.-L.; Liu, Y.; Wang, W.-N.; Luo, Q.; Li, Q.-S.Acta Chim. Sinica2005, 63, 1554 (in Chinese).(王文亮, 刘艳, 王渭娜, 罗琼, 李前树, 化学学报, 2005, 63, 1554.)32 Han, J. H.; Gao, G.; Widjaja, Y.; Garfunkel, E; Musgrave,C. B. Surf. Sci. 2004, 550, 199.33 Kukli, K.; Forsgren, K.; Aarik, J.; Uustare, T.; Aidla, A.;Niskanen, A.; Ritala, M.; Leskelä, M.; Hårsta, A. J. Cryst.Growth2001, 231, 262.(A0510175 SONG, J. P.; DONG, H. Z.)。

在硫酸钠熔盐中合成莫来石晶须

在硫酸钠熔盐中合成莫来石晶须.txt爱人是路，朋友是树，人生只有一条路，一条路上多棵树，有钱的时候莫忘路，缺钱的时候靠靠树，幸福的时候别迷路，休息的时候靠靠树！本文由suxiaohua84752贡献pdf文档可能在WAP端浏览体验不佳。

建议您优先选择TXT，或下载源文件到本机查看。

NA IHUO CA I I O /耐火材料 LA2006 , 40 ( 3 ) 165 ～168研发与应用在硫酸钠熔盐中合成莫来石晶须朱伯铨李雪冬瑞郝汪厚植武汉科技大学高温陶瓷与耐火材料湖北省重点实验室武汉 430081 摘要采用 A l2 ( SO4 ) 3 ?18H2 O 和 SiO2 作为反应原料 , 在 Na2 SO4 熔盐中合成了莫来石晶须 , 利用 XRD、 FESEM 和 SEM 等手段研究了合成产物的组成和形貌 , 并研究了合成温度( 700 ℃、 800 ℃、 900 ℃、 950 ℃、1000 ℃、 1100 ℃ 1200 ℃) 、和熔盐用量 (反应料与 Na2 SO4 的质量比分别为 2: 1、 1、 2 和 1: 4 ) 、 1: 1: 保温时间 ( 2 h、 h和 4 h )等工艺因素对合成反应的影响。

结果表明 : 用熔盐法合成的莫来石不含其他晶相 , 纯度高 , 晶 3 须直径在 50 ～150 nm ,长度为 3 ～8 μm。

研究还发现 : Na2 SO4 熔盐的合适用量为反应料与 Na2 SO4 的质量比是1: 1,此时 ,混合料在 900 ℃开始生成莫来石 , 950 ℃石英相基本消失 , 1000 ℃保温 3 h 合成反应基本完成 ,超过 1100 ℃ ,合成的莫来石开始分解。

因此 ,熔盐法合成莫来石的合理温度为 1000 ℃时保温 3 h。

关键词熔盐法 ,硫酸钠 ,莫来石 ,晶须莫来石陶瓷的高温物理化学性质稳定 , 熔点高 , 热膨胀系数小 ,而且其强度和韧性随着温度的升高不仅不衰减反而大幅度提高 ,所以莫来石的应用极其广泛[1 - 3]100 ℃干燥 ,以去除吸附水 , 按 A l2 O3 与 SiO2 物质的量比为 3: 2 准确称取 A l2 ( SO4 ) 3 ?18H2 O 和 SiO2 , 置于刚玉行星球磨罐中 , 加入适量刚玉球 , 以 250r?m in 的转速 , 在行星球磨机上研磨 10 m in, 取出- 1。

CO在金属掺杂TiO2纳米管阵列中的吸附及氧化

[Article]物理化学学报(Wuli Huaxue Xuebao )Acta Phys.-Chim.Sin.2012,28(1),44-50JanuaryReceived:September 6,2011;Revised:October 10,2011;Published on Web:October 28,2011.∗Corresponding author.Email:jgw@;Tel:+86-571-88871037.The project was supported by the National Natural Science Foundation of China (20906081)and Natural Science Foundation of Zhejiang Province,China (R4110345).国家自然科学基金(20906081)和浙江省自然科学基金(R4110345)资助项目ⒸEditorial office of Acta Physico-Chimica SinicaCO 在金属掺杂TiO 2纳米管阵列中的吸附及氧化董华青潘西谢琴孟强强高建荣王建国*(浙江工业大学化学工程与材料学院,杭州310014)摘要:采用密度泛函理论(DFT)研究了五种不同金属元素V 、Cr 、Pd 、Pt 、Au 掺杂二氧化钛纳米管阵列(TNTAs)的性质以及CO 在这些二氧化钛纳米管阵列中的吸附和氧化.结果表明:金属的掺杂使TNTAs 的带隙减小;弱吸附的CO 能够和二氧化钛纳米管阵列中的晶格氧通过氧化还原机理生成CO 2,这可归因于纳米管阵列的限域效应和金属元素的掺杂.合适的金属掺杂能促进CO 氧化,除Cr 以外的金属元素的掺杂降低了CO 氧化的活化能垒,特别是Pd 或Au 的掺杂使能垒降低最为明显.贵金属元素Pd 或Au 掺杂TiO 2纳米管阵列具有优良的光催化性能,可用于CO 的低温氧化催化剂.关键词:密度泛函理论;二氧化钛纳米管阵列;一氧化碳氧化中图分类号:O641;O647CO Adsorption and Oxidation on Metal-DopedTiO 2Nanotube ArraysDONG Hua-Qing PAN XiXIE Qin MENG Qiang-Qiang GAO Jian-RongWANG Jian-Guo *(College of Chemical Engineering and Materials Science,Zhejiang University of Technology,Hangzhou 310014,P .R.China )Abstract:Density functional theory (DFT)calculations were used to investigate the structural and electronic properties of V-,Cr-,Pd-,Pt-,and Au-doped titania nanotube arrays (TNTAs)where Ti was replaced by dopants.The adsorption of CO and the formation of CO 2on these various nanotube arrays were also studied in detail.We found that CO physisorbed weakly inside the TNTAs and CO was oxidized by lattice oxygen to form CO 2by the redox mechanism.This may thus be attributed to the unique confinement effect and to different metal doping.All the metal doped systems except the Cr-TNTAs showed a lower activation energy barrier than the undoped TNTAs,indicating that proper metal dopants can promote CO oxidation.The reaction on the Pd-or Au-doped TNTAs had the lowest barrier.Therefore,we found that Pd-or Au-doped TNTAs led to enhanced catalytic activity for CO oxidation at low temperatures.Key Words:Density functional theory;TiO 2nanotube arrays;CO oxidation1引言纳米半导体光催化剂TiO 2、ZnO 、CdS 、WO 3、Fe 2O 3等具有不同于体相材料的独特催化性能,1其中半导体纳米TiO 2具有光催化活性高、氧化力强、化学稳定性好、成本低廉和无毒等优点,2-4在太阳能电池、5,6气体传感器、7光解水制氢8及有机污染物降解9等能源利用和环境保护方面备受青睐.自从电化学阳极氧化法成功合成自组装的二氧化钛纳米doi:10.3866/PKU.WHXB2012284444董华青等:CO在金属掺杂TiO2纳米管阵列中的吸附及氧化No.1管(TNTs)以来,10TiO2的研究进入了新阶段.与其他形态的TiO2(如纳米粉体和薄膜)相比,TNTs因具有更大的比表面积、较强的吸附能力、高度有序的结构而作为催化剂或催化剂载体.11-15理论研究表明,和体相锐钛矿类似,TNTs是宽带隙的半导体,16光催化量子效率和太阳光利用率低.为了提高其光催化活性,金属元素掺杂是一种有效的方法.17掺杂可以改变催化剂的晶体结构、尺寸以及表面性质,掺杂金属离子作为有效的电子捕获阱,显著延长了电子与空穴复合的时间.18-20CO的催化氧化在CO气体传感器、燃料电池中CO的消除以及空气污染治理,尤其是汽车尾气排放控制中有着重要的现实作用.21汽车尾气净化器中所用的Pt/Rh/Pd及载体组成的三效热催化剂(TWCs)因需要在200°C以上才能氧化大部分CO,22,23研究者从理论或实验上开发了CO的低温氧化催化剂,如纳米Au、21,24螺旋形Au纳米管、25TiO2粉末或掺Pt的TiO2颗粒、19,26,27Pd/TiO2粉末、28Au/ TiO2颗粒、29-32TNTs,33但却存在热力学不稳定的问题.为了有效抑制Au粒子的聚集,提高金催化剂的稳定性,刘玉良等34以大肠杆菌为模板,制得氧化钛包裹纳米金粒子的杆状催化剂Au@TiO2.俞俊等35向Au/TiO2催化剂中添加稀土助剂La2O3,使TiO2的晶格应变增强,提高了CO的氧化速率.迄今,对金属元素掺杂的TNTs用于CO的低温氧化研究较少. Ntho等36发现CO在Au/TNTs上氧化形成的中间物种重碳酸盐易使催化剂失活.Chien等11用原位红外光谱研究水热合成的Pt/TNTs和Au/TNTs,发现二者的催化活性会因TNTs的高比表面积而显著增强,但Pt/TNTs的催化活性比Au/TNTs更高,前者有助于CO2还原,后者有助于CO低温氧化.而Akita等37应用沉淀浸渍法制备了Au/TNTs,透射电镜(TEM)观察TNTs的晶体结构不同于金红石或锐钛矿型TiO2,Au/TNTs用于CO氧化的催化活性比Au/TiO2 (金红石或锐钛矿)粉末更低.文献中对金属掺杂二氧化钛纳米管阵列(TNTAs)用于CO氧化的理论研究却较少.我们已经系统研究了二氧化钛纳米管38,39以及其他金属氧化物纳米管40的形成、几何构型与电子结构性质,建立了二氧化钛纳米管阵列的理论模型并研究了水在其中的分解性质.39本文采用密度泛函理论方法研究了V、Cr、Pd、Pt和Au五种不同金属掺杂取代Ti的二氧化钛纳米管阵列的性质,尤其是金属掺杂对CO被晶格氧氧化的催进作用.2计算方法本文采用基于密度泛函理论的第一性原理,全部计算在Materials Studio中的DMol3模块41,42上完成.计算时电子交换相关作用采用广义梯度近似(GGA)的PW9143交换关联势描述.价电子波函数采用双数值基加极化函数(DNP)展开,它相当于Gaussian中6-31G**基组.布里渊区积分的Monk-horst-Pack网格参数设置为2×2×4.结构优化中,能量的收敛标准为1×10-5Ha,力收敛标准为2×10-4 Ha·nm-1.反应的过渡态搜索采用LST/QST方法进行,并进一步做验证.TNTAs是由重构的单层金红石(110)薄片建立的最稳定二氧化钛纳米管(6,6)形成.39其单元晶胞尺寸为14.2nm×14.2nm×8.91nm,包含36个钛原子和72个氧原子.3结果和讨论3.1金属掺杂TiO2纳米管阵列的几何与电子结构性质图1为二氧化钛纳米管(6,6)阵列的模型.在该几何结构中,虽然所有钛原子的配位数均为6,但是由于周围环境中氧原子位置的影响,钛原子可分为两种,即M1和M2.因而在对TiO2纳米管阵列掺杂改性时,我们考察用金属原子替代这两类不同位置上的钛原子.为了比较V、Cr、Pd、Pt和Au五种金属掺杂TNTAs的难易程度和掺杂后结构的稳定性,计算了杂质形成能.形成能E form定义为：E form=E(M+TNTAs)-[E(TNTAs)+E(M)-E(Ti)]图1金属掺杂TiO2纳米管阵列示意图Fig.1Scheme of metal-doped TNTAs45Acta Phys.⁃Chim.Sin.2012V ol.28其中,E (M+TNTAs)为掺杂体系总能量,E (TNTAs)为完美的TiO 2纳米管阵列的能量,E (M)(M=V 、Cr 、Pd 、Pt 、Au)为掺杂金属体材料的能量,E (Ti)为Ti 体材料的能量.此种方法已用于卤素掺杂TiO 2、44过渡金属掺杂钛酸纳米管45等体系来计算形成能.形成能为正,说明掺杂取代过程需要吸收一定的能量,该值越低,越容易掺杂,掺杂体系越稳定.所有金属掺杂体系的形成能如表1所示,可以看出:每种金属在M 1和M 2取代位的掺杂都需要能量,除Au 以外的金属在M 1位的形成能稍稍低于M 2位的(差值小于0.20eV),说明金属替代两种Ti 位出现的几率差不多.比较这五种金属的形成能,Au 掺杂体系最大,Cr 体系最小,表明Au 掺杂TNTAs 较其他四种体系并不十分稳定;贵金属Au 、Pd 、Pt 体系的形成能远高于V 和Cr 体系,意味着在实验制备中贵金属离子需要较高的能量才能掺入TNTAs 中,而Cr 和V 很容易取代,这是因为V 4+、Cr 4+与Ti 4+的离子半径相近(V 4+0.0580nm 、Cr 4+0.0560nm 、Ti 4+0.0605nm).46金属掺杂后,掺杂原子附近的几何构型发生了较大的变化.无论是M 1位还是M 2位取代,Au 、Pd 和Pt 的引入使附近的氧原子有远离掺杂原子的趋势,掺杂原子与氧原子的平均键长比原位Ti 与O 的平均键长更大,特别是Au 取代导致其配位氧原子数不再是6,而是5,取代处形成的点缺陷破坏了原有原子间作用力的平衡,造成近邻的氧原子偏离其平衡位置.而Cr 和V 的掺杂取代使掺杂原子与氧原子的平均键长比原位Ti 与O 的平均键长要小,但对TNTAs 的整体结构影响不大,几乎不会发生阵列的畸变,其对称性与完美TNTAs 几乎一致.总之,掺杂促使掺杂金属原子附近的氧原子的活性发生了改变,有利于催化反应.而掺杂体系表现的不同性质与各掺杂金属原子半径、电负性和外层电子的排布等有关.为了清楚地说明各金属掺杂对TNTAs 电子结构的影响,图2(a,b)分别给出了五种金属掺杂TNTAs 前后的总态密度以及在带隙附近的各原子的分态密度图(取费米能级为能量零点).由图2可知,对于完美TNTAs,费米能级附近的价带主要由O 原子2p 轨道上的电子组成,导带主要由Ti 原子3d 轨道上的电子组成.对于掺杂体系,在禁带出现了一个新的态密度峰,这是掺杂金属的d 能态(V 3d ,Cr 3d ,Pt 5d ,Pd 4d ,Au 5d )参与导带形成的结果,从而使掺杂TNTAs 的导带向低能端移动,带隙缩小.对于Pt 和Pd 掺杂,价带顶不动,只是导带向低能级表1金属原子掺杂TiO 2纳米管阵列的形成能Table 1Formation energies of metal-doped TNTAsE 1and E 2represent formation energies relative to M 1-andM 2-doped sites,respectively.V-TNTAs Cr-TNTAs Pt-TNTAs Pd-TNTAs Au-TNTAsE 1/eV0.4372.6337.91610.57414.145E 2/eV 0.4422.6548.10510.75314.084图2金属掺杂TNTAs 前后的总态密度图(a)和分态密度图(b)Fig.2Total DOS (a)and partial DOS (b)of TNTAs before and after metal-doping46董华青等:CO 在金属掺杂TiO 2纳米管阵列中的吸附及氧化No.1移动,而V 、Cr 和Au 掺杂均使价带和导带向低能级移动,可认为费米能级升高了.对于Pd 和V 掺杂,杂质峰出现在禁带中靠近导带底的位置,电子有可能从价带顶部直接跃迁至杂质能带,使TNTAs 吸收带红移,这与V 掺杂锐钛矿相TiO 2引起带隙减小具有相似的效应.47对于Cr 掺杂体系,杂质峰穿过费米能级,电子在该能带上是未充满状态,具有很高的活性,体系体现出金属性.杂质峰强度较大,即电子在其上存在的概率较大,价带中的电子可以先跃迁到该杂质能级中,再吸收能量较小的光子跃迁到导带,从而拓宽TNTAs 光吸收范围,这与Ghicov 等48使用Cr 掺杂的TNTAs 在紫外区和可见光区的响应均明显增强的实验结果相符,而Cr 掺杂体相锐钛矿TiO 2却使带隙增大0.06eV .49Au 体系的杂质峰类似Cr 体系,也几乎出现在禁带中间,但杂质峰强度不同.Pt 掺杂对带隙宽度影响最小,杂质峰并不很明显,价带顶几乎不动,导带稍微向低能端移动.3.2CO 在金属掺杂TiO 2纳米管阵列中的吸附对于自由的CO 分子,计算得到C ―O 键键长是0.1141nm,与实验值(0.1128nm)50吻合较好,说明所采用方法的精确性.为便于比较CO 在五种金属掺杂TNTAs 上的吸附和氧化反应情况,均考查M 1取代位.图3为CO 在这些纳米管阵列中吸附的优化构型.相关几何参数(如碳原子和阵列氧原子的最近距离d C ―Oa ,CO 的键长d C ―O b )和吸附能E a 如表2所示.由图3可知,CO 分子和各纳米管阵列均没有成键;从吸附能数据来看,均为弱的物理吸附.V 、Pt 或Pd 掺杂TNTAs 和完美TNTAs 的吸附能一致,均为-0.14eV ,比Au 或Cr 体系的吸附能更负,吸附更强.虽然CO 分子的键长均相等且优化前后几乎不变,但与完美TNTAs 相比,掺杂体系中碳原子和晶格氧的最近距离减小,O a ―C ―O b 的角度也减小,说明金属元图3CO 在金属掺杂TiO 2纳米管吸附的优化构型Fig.3Optimized geometries of CO adsorption on M 1-doped TiO 2nanotube arraysdistances in nm,angles in degree表2各纳米管阵列中CO 氧化反应优化的初态(IS)、过渡态(TS)和终态(FS)结构的几何参数及CO 的吸附能(E a )Table 2Optimized geometric parameters of initial state (IS),transition state (TS),final state (FS),andadsorption energy (E a )of CO on various TNTAsO a denotes the lattice oxygen atom in the arrays which binds with the dopant and has the closest distance from theC atom of CO.O b indicates the O atom of CO.d means the distances.TNTAs V-TNTAs Cr-TNTAs Pt-TNTAs Pd-TNTAs Au-TNTAsd C —O a /nmIS0.34110.32590.32250.31080.32040.3194TS 0.17780.17900.17620.18200.18390.1897FS 0.11890.11880.11880.11810.11820.1180d C —O b /nm IS 0.11390.11390.11390.11390.11390.1139TS 0.11520.11520.11600.11510.11460.1151FS 0.11580.11590.11590.11670.11660.1167∠O a CO b /(°)IS 141.414123.545101.301113.567121.141116.660TS 122.981119.906119.255119.842119.629120.597FS 179.317179.621179.713179.705179.738179.779E a /eV -0.14-0.14-0.11-0.14-0.14-0.1247Acta Phys.⁃Chim.Sin.2012V ol.28素的掺杂有利于CO 与阵列的相互作用.3.3CO 在金属掺杂TiO 2纳米管阵列上的氧化CO 弱吸附后,我们进一步研究了CO 和TNTAs 的晶格氧反应生成CO 2的反应.图4示出了在六种模型上反应所得到的过渡态结构,其几何参数如表2所示.可以看出所有二氧化钛纳米管阵列体系中的掺杂原子和参与反应的晶格氧O a 的键长变长,C 与O a 之间的平均距离缩短,∠O a CO b 均在120°左右,这样的弯曲结构使得CO 分子的C 端可以更加靠近O a ,O a 端受CO 附近的管内表面氧原子的更大排斥,导致更短的O a ―CO 距离和更大的∠O a CO b 角度.处于过渡态的CO 偏离了初始状态,C ―O b 键均被拉长,说明CO 分子被活化了.CO 氧化反应的终态几何参数如表2所示.在每种纳米管阵列的终态结构中,∠O a CO b 均接近180°,C 与O b 键长变大,CO 中C ―O 键轻微活化;C 与O a 的距离较初态和过渡态减小,成键作用得到强化,均对CO 氧化起到促进作用.氧化产物在结构上接近计算得到的自由CO 2分子(两个C ―O 键长0.1175nm,键角180°),由于CO 2气体分子非常稳定,相对不活泼,CO 2和管表面只有很弱的相互作用,会很快脱附.比较CO 在六种体系中的氧化反应情况,尽管CO 吸附的结构不同,但产物CO 2在V 、Cr 这两种掺杂体系及完美TNTAs 中的结构均很相似,在三种贵金属掺杂中的结构也表现出相似性,但后者的C ―O 平均键长显著高于前者.这种差异与掺杂离子的稳定氧化态、离子半径、掺杂原子与氧原子的配位环境等有密切关系.51搜索CO 氧化的过渡态,可以知道CO 在掺杂纳米管阵列中的氧化遵循氧化还原机理,即所谓的Mars-van Krevelen 机理:52CO 吸附在纳米管阵列中,因纳米管阵列中与掺杂原子和钛原子共同成键的晶格氧原子活性高于其他氧原子,CO 与该晶格氧原子发生氧化反应生成CO 2,CO 2解吸后形成氧空缺,纳米管阵列处于还原态,会被来自气相中的氧氧化.这与DFT 研究CO 在Au 掺杂金红石TiO 2(110)表面53和锐钛矿TiO 2(001)表面54的氧化机理一样.事实上,CO 和完美体相二氧化钛表面氧原子很难发生反应,当表面氧原子处于低配位和碱性较强时,CO 才有可能与该活性晶格氧反应生成CO 2,54故CO 能与TiO 2纳米管阵列中的晶格氧反应可归因于纳米管阵列所具有的限域效应.为了更直观地认识CO 在不同金属掺杂TNTAs 中氧化反应的能量变化,图5给出反应过程中初态、过渡态、终态结构的势能面图,以CO 吸附前的体系能量为能量零点.可以看出,与完美TNTAs 相比,CO 在金属掺杂TNTAs 中氧化放出的热量更多.Cr 掺杂使反应能垒升高,不利于CO 的氧化;V 掺杂的能垒比完美TNTAs 的能垒低0.03eV ,几乎没有改变.Pd 、Pt 或Au 掺杂使能垒明显降低,特别是贵金属元素Pd 或Au 掺杂的反应活化能最低,均为0.34eV ,比CO 在体相金红石TiO 2表面的氧化反应能垒(0.56eV)55低得多,这是纳米管阵列独特的物化特性和不同金属掺杂导致的.这说明合适的金属元素掺杂能使TiO 2纳米管阵列有更高的催化活性,从而促图4CO 在金属掺杂TNTAs 中氧化的过渡态的优化构型Fig.4Optimized geometries of transition state of CO oxidation by lattice oxygen of M 1-doped TNTAsdistances in nm,angles in degree48董华青等:CO 在金属掺杂TiO 2纳米管阵列中的吸附及氧化No.1进CO 在较低的温度下氧化.4结论采用密度泛函理论研究了五种不同的金属V 、Cr 、Pd 、Pt 、Au 掺杂二氧化钛纳米管阵列的几何与电子结构性质,特别研究了CO 在其中的吸附及氧化机理.结果表明,金属原子的掺杂使二氧化钛纳米管阵列的带隙减小,光催化活性有所提高.CO 以物理吸附方式弱吸附在六种纳米管阵列中,尽管吸附很弱,但能与晶格氧通过氧化还原机理生成CO 2,而CO 和体相二氧化钛表面的氧原子很难发生反应,可以认为管腔独特的限域环境使CO 能在二氧化钛纳米管阵列中得以催化氧化.合适的金属掺杂能促进CO 氧化,除Cr 以外的金属元素的掺杂降低了反应能垒,特别是贵金属Pd 或Au 的掺杂使能垒降低最为明显.Pd 或Au 掺杂TiO 2纳米管阵列这种优良的光催化剂可用于暗条件下CO 的低温氧化.References(1)Hoffman,M.R.;Martin,S.T.;Choi,W.;Bahnemann,D.W.Chem.Rev.1995,95(1),69.(2)Tachikawa,T.;Tojo,S.;Fujitsuka,M.;Majima,T.J.Phys.Chem.B 2004,108,11054.(3)Macak,J.M.;Tsuchiya,H.;Schmuki,P.Angew.Chem.Int.Edit.2005,44,2100.(4)Ivanovskaya,V .V .;Enyashin,A.N.;Ivanovskii,A.L.Mendeleev Commun.2003,13(1),5.(5)Gr ätzel,M.Nature 2001,414,338.(6)Zhu,K.;Neale,N.R.;Miedaner,A.;Frank,A.J.Nano Lett.2007,7(1),69.(7)Varghese,O.K.;Gong,D.;Paulose,M.;Ong,K.G.;Dickey,E.C.;Grimes,C.A.Adv.Mater.2003,15,624.(8)Fujishima,A.;Honda,K.Nature 1972,238,37.(9)Rivera,A.P.;Tanaka,K.;Hisanaga,T.Appl.Catal.B 1993,3(1),37.(10)Gong,D.;Grimes,C.A.;Varghese,O.K.;Hu,W.C.;Singh,R.S.;Chen,Z.;Dickey,E.C.J.Mater.Res.2001,16,3331.(11)Chien,S.H.;Liou,Y .C.;Kuo,M.C.Synth.Met.2005,152,333.(12)Idakiev,V .;Yuan,Z.Y .;Tabakova,T.;Su,B.L.Appl.Catal.A 2005,281,149.(13)Bavykin,D.V .;Lapkin,A.A.;Plucinski,P.K.;Friedrich,J.M.;Walsh,F.C.J.Catal.2005,235,10.(14)Tsai,C.C.;Teng,H.Chem.Mater.2004,16,4352.(15)Zhu,B.;Guo,Q.;Huang,X.;Wang,S.;Zhang,S.;Wu,S.;Huang,W.J.Mol.Catal.A 2006,249,211.(16)Enyashin,A.N.;Seifert,G.Phys.Stat.Sol.B 2005,242,1361.(17)Akpan,U.G.;Hameed,B.H.Appl.Catal.A 2010,375,1.(18)Ishitani,O.;Inoue,C.;Suzuki,Y .;Ibusuki,T.J.Photochem.Photobiol.A-Chem.1993,72,269.(19)Linsebigler,A.L.;Lu,G.;Yates,J.T.,Jr.Chem.Rev.1995,95,735.(20)Murruni,L.;Leyva,G.;Litter,M.I.Catal.Today 2007,129,图5CO 在金属掺杂TNTAs 中氧化的能量图Fig.5Potential energy diagrams of CO oxidation on M 1-dopedTNTAs49Acta Phys.⁃Chim.Sin.2012V ol.28127.(21)Min,B.K.;Friend,C.M.Chem.Rev.2007,107,2709.(22)Campbell,C.T.Science2004,306,234.(23)Corti,C.W.;Holliday,R.J.;Thompson,D.T.Appl.Catal.A2005,291,253.(24)Haruta,M.;Yamada,N.;Kobayashi,T.;Iijima,S.J.Catal.1989,115,301.(25)An,W.;Pei,Y.;Zeng,X.C.Nano Lett.2008,8(1),195.(26)Einaga,H.;Harada,M.;Futamura,S.;Ibusuki,T.J.Phys.Chem.B2003,107,9290.(27)V orontsov,A.V.;Savinov,E.N.;Barannik,G.B.;Troitsky,V.N.;Parmon,V.N.Catal.Today1997,39,207.(28)Zhang,M.;Jin,Z.S.;Wang,S.B.;Zhang,S.L.;Zhang,Z.J.Acta Phys.-Chim.Sin.2003,19,100.[张敏,金振声,王守斌,张顺利,张治军.物理化学学报,2003,19,100.](29)Valden,M.;Lai,X.;Goodman,D.W.Science1998,281,1647.(30)Boccuzzi,F.;Chiorino,A.;Manzoli,M.;Lu,P.;Akita,T.;Ichikawa,S.;Haruta,M.J.Catal.2001,202,256.(31)Chen,M.S.;Goodman,D.W.Science2004,306,252.(32)Chen,M.;Cai,Y.;Yan,Z.;Goodman,D.W.J.Am.Chem.Soc.2006,128,6341.(33)Vesborg,P.C.K.;In,S.-I.;Olsen,J.L.;Henriksen,T.R.;Abrams,B.L.;Hou,Y.;Kleiman-Shwarsctein,A.;Hansen,O.;Chorkendorff,I.J.Phys.Chem.C2010,114,11162.(34)Liu,Y.L.;You,C.R.;Li,Y.;He,T.;Zhang,X.Q.;Suo,Z.H.Acta Phys.-Chim.Sin.2010,26,2455.[刘玉良,由翠荣,李杨,何涛,张香芹,索掌怀.物理化学学报,2010,26,2455.] (35)Yu,J.;Wu,G.S.;Mao,D.S.;Lu,G.Z.Acta Phys.-Chim.Sin.2008,24,1751.[俞俊,吴贵升,毛东森,卢冠忠.物理化学学报,2008,24,1751.](36)Ntho,T.A.;Anderson,J.A.;Scurrell,M.S.J.Catal.2009,261,94.(37)Akita,T.;Okumura,M.;Tanaka,K.;Ohkuma,K.;Kohyama,M.;Koyanagi,T.;Date,M.;Tsubota,S.;Haruta,M.Surf.Interface Anal.2005,37,265.(38)Meng,Q.Q.;Wang,J.G.;Xie,Q.;Li,X.N.J.Phys.Chem.C2010,114,9251.(39)Meng,Q.Q.;Wang,J.G.;Xie,Q.;Dong,H.Q.;Li,X.N.Catal.Today2011,165,145.(40)Su,Y.;Meng,Q.Q.;Wang,J.G.J.Phys.Chem.C2009,113,21338.(41)Delley,B.J.Chem.Phys.1990,92,508.(42)Delley,B.J.Chem.Phys.2000,113,7756.(43)Perfew,J.P.;Wang,Y.Phys.Rev.B1992,45,13244.(44)Yang,K.S.;Dai,Y.;Huang,B.B.;Whangbo,M.H.Chem.Mater.2008,20,6528.(45)Le,L.C.;Ma,X.G.;Tang,H.;Wang,Y.;Li,X.;Jiang,J.J.ActaPhys.Sin.2010,59,1314.[乐伶聪,马新国,唐豪,王扬,李翔,江建军.物理学报,2010,59,1314.](46)Yao,Y.B.;Xie,T.;Gao,Y.M.Handbook of PhysicalChemistry;Shanghai Science and Technology Press:Shanghai,1985;pp99-104.[姚允斌,解涛,高英敏.物理化学手册.上海:上海科学技术出版社,1985:99-104.](47)Xu,L.;Tang,C.Q.;Huang,Z.B.Acta Phys.-Chim.Sin.2010,26,1401.[徐凌,唐超群,黄宗斌.物理化学学报,2010,26,1401.](48)Ghicov,A.;Schmidt,B.;Kunze,J.;Schmuki,P.Chem.Phys.Lett.2007,433,323.(49)Yang,K.;Dai,Y.;Huang,B.ChemPhysChem2009,10,2327.(50)Lide,D.R.CRC Handbook of Chemistry and Physics,76th ed.;CRC Press:New York,1996.(51)Pala,R.G.S.;Metiu,H.J.Phys.Chem.C2007,111,8617.(52)Mars,P.;van Krevelen,P.W.Chem.Eng.Sci.1954,3,41.(53)Chretien,S.;Metiu,H.Catal.Lett.2006,107,143.(54)Mguig,B.;Calatayud,M.;Minot,C.J.Mol.Struct.-Theochem2004,709,73.(55)Wang,Z.;Zhao,Y.;Cui,X.;Tan,S.;Zhao,A.;Wang,B.;Yang,J.;Hou,J.G.J.Phys.Chem.C2010,114,18222.50。

211064127_逆水煤气变换反应研究进展

化工进展Chemical Industry and Engineering Progress2023 年第 42 卷第 3 期逆水煤气变换反应研究进展王晓月，张伟敏，姚正阳，郭晓宏，李聪明（太原理工大学省部共建煤基能源清洁高效利用国家重点实验室，山西太原 030024）摘要：逆水煤气变换（RWGS ）反应是将二氧化碳（CO 2）加氢转化为甲醇、低碳烯烃、芳烃以及汽油等高附加值化学品和燃料的关键步骤，对于实现CO 2资源化利用具有重要意义。

本文综述了近年来RWGS 反应的研究进展，包括RWGS 反应热力学分析、催化机理、可选择的催化剂种类以及提升催化剂性能策略等方面。

文章从热力学角度分析，RWGS 反应在高温下有利，而低温下存在甲烷化竞争反应。

RWGS 反应机理主要包括氧化还原机理以及缔合机理，其中缔合机理包括甲酸盐路径和羧酸盐路径等。

相比于其他催化体系，负载型金属催化剂展现出较优异的RWGS 反应性能。

另外，通过添加碱金属助剂、形成双金属合金以及选择合适载体和减小金属颗粒尺寸以优化金属-载体相互作用等手段可实现低温高效稳定的RWGS 反应催化剂的设计开发。

关键词：逆水煤气变换反应；二氧化碳；一氧化碳；热力学；催化剂中图分类号：TQ073 文献标志码：A 文章编号：1000-6613（2023）03-1583-12Research progress of reverse water gas shift reactionWANG Xiaoyue ，ZHANG Weimin ，YAO Zhengyang ，GUO Xiaohong ，LI Congming(State Key Laboratory of Clean and Efficient Coal Utilization, Taiyuan University of Technology, Taiyuan 030024, Shanxi, China)Abstract: Reverse water gas conversion (RWGS) reaction is a key step in the catalytic hydrogenation ofcarbon dioxide (CO 2) to high value-added chemicals and fuels such as methanol, light olefins, aromatics and gasoline, which is of great significance for the utilization of CO 2. This review summarizes the research progress of RWGS reaction in recent years, including thermodynamic analysis of RWGS reaction, catalytic mechanisms, selective catalysts and strategies to improve the performance of catalysts. From the perspective of thermodynamics, RWGS reaction is favorable at high temperature, as methanation reaction emerges at low temperature. The mechanisms of RWGS reaction mainly consist of redox mechanism and association mechanism, and the latter further contains a formate route and/or carboxylate route. Compared with other catalyst system, supported metal catalysts commonly exhibit a superior RWGS reaction performance. In addition, the rational design of RWGS reaction catalysts with high reactivity and durability could be realized by adding alkali metal additives, forming bimetallic alloy as well as modulating the metal-support interaction via selecting a good support or reducing the metal particle size.Keywords: reverse water gas shift reaction; carbon dioxide; carbon monoxide; thermodynamics; catalyst综述与专论DOI ：10.16085/j.issn.1000-6613.2022-0816收稿日期：2022-05-05；修改稿日期：2022-07-13。

碳酸锰的几种漂亮结构

Yu Qiao, Si-Rong Li, Yan Yu and Chun-Hua Chen*
Yolk-structured microspheres of spinel LiMn2O4 are successfully prepared by a specially designed multi-step synthesis procedure involving precipitation, controlled oxidation, selective etching and chemical lithiation. Solid-structured and hollow-structured LiMn2O4 are also synthesized by a similar method for comparison. X-ray diﬀraction, scanning electron microscopy, transmission electron microscopy, Brunauer–Emmett–Teller method and IR spectroscopy are employed to study their structures and compositions. The electrochemical
case of large particle sizes. Although the nano-structured LiMn2O4 is very eﬀective in improving the rate capability, the low tap density of nano-sized powders directly leads to the low energy density of a cell. To achieve a high tap density, electrode materials are preferred to have micron-sized particles, especially with spherical shapes which can pack more densely.21–25 In our study, we want to nd a balance between high tap density and short diﬀusion distance. Inspired by the work of Qian et al. who have synthesized hollow structures of Mn2O3, MnO2 and Mn2O3 microspheres,26–28 we design and synthesize a special yolk-structured LiMn2O4 microsphere (Scheme 1b). In this structure model, the outer shell is porous and composed of many nanoparticles, which can enlarge the specic surface area of the electrode and provide more reaction sites for lithium insertion and extraction. The core is relatively dense to increase the volumetric energy density. The spacing between the shell and the core can buﬀer any volume change of the core during heating/cooling or charge/discharge. In the present work, we rst synthesize a yolk-structured Mn2O3 as a precursor and then follow a simple solid-state reaction or chemical lithiation to produce the yolk-structured LiMn2O4 microsphere (LMO-Y) (Scheme 1a). Moreover, we compare the electrochemical performance of LMO-Y with those of hollow LiMn2O4 microspheres (LMO-H) (Scheme 1c) and solid LiMn2O4 microspheres (LMO-S) (Scheme 1d).

CO在Cu(100)表面最佳吸附位研究

CO在Cu(100)表面最佳吸附位研究赵国利;刘丹;刘实;张晓彤;孙兆林【期刊名称】《辽宁化工》【年(卷),期】2005(034)002【摘要】采用密度泛函理论(DFT)对CO分子在Cu(100)表面上的吸附行为进行了研究.计算结果表明:顶位吸附和桥位吸附这两种模型中CO分子都倾斜地吸附在Cu原子上,其中顶位吸附的C-O键长(0.115 5 nm)和Cu-C键长(0.184 0 nm)与实验值符合得很好,而且C-O键长均比自由CO分子的C-O键长要长,说明Cu原子活化了CO分子.另外,顶位吸附时的体系能量较低,且有较大的吸附能,说明顶位吸附模型更稳定,所以CO很可能采用顶位吸附模型.从Mulliken轨道分布数据可以看出Cu原子上的σ电子向Cu原子的4p轨道和O原子的2p轨道转移,从而CO 分子上的电子云会发生重排,组成新的轨道,所以CuCO就会形成弯曲结构.【总页数】4页(P58-60,63)【作者】赵国利;刘丹;刘实;张晓彤;孙兆林【作者单位】辽宁石油化工大学石油化工学院,辽宁,抚顺,113001;辽宁石油化工大学石油化工学院,辽宁,抚顺,113001;辽宁石油化工大学石油化工学院,辽宁,抚顺,113001;辽宁石油化工大学石油化工学院,辽宁,抚顺,113001;辽宁石油化工大学石油化工学院,辽宁,抚顺,113001【正文语种】中文【中图分类】O641.12【相关文献】1.CO在修饰的邻位Cu(100)表面低温吸附的对比研究 [J], Przemyslaw JanGodowski;Jens Onsgaard2.DOPA醌在Cu(100)表面吸附的密度泛函理论研究 [J], 周太刚;王伯初;陈双扣;冯莹柱;梁华民;杨丽君3.丙烯腈在Cu(100)表面化学吸附的密度泛函理论研究 [J], 夏树伟;高林娜;徐香;孙雅丽;夏少武4.Pd(Cu)在MgO(100)表面吸附CO和O2的理论研究 [J], 郝兰;王艳;陈光巨5.噻吩在Ni(100),Cu(100),Co(100)表面吸附的密度泛函研究 [J], 赵亮;陈燕;高金森;陈玉因版权原因，仅展示原文概要，查看原文内容请购买。

水分子和二氧化铈（111）表面相互作用的DFT+U研究

水分子和二氧化铈（111）表面相互作用的DFT+U研究水分子和二氧化铈(111)表面相互作用的DFT+U研究王清高;杨宗献;危书义【期刊名称】《物理化学学报》【年(卷),期】2009(025)012【摘要】The interaction of water molecule and a ceria (111) surface was investigated using DFT+U (density functional theory with the inclusion of on-site Coulomb interaction by introducing Hubbard U parameter) method. The results show that water molecules adsorb on the oxidized ceria (111) surface through a single H-bond configuration and they do not decompose. On a reduced ceria (111) surface, the water molecules adsorb through a non-H-bond configuration. Furthermore, water molecules prefer to dissociate and form a hydroxyl surface. The hydroxyl surface is much more stable than the physisorption state of H_2 on the oxidized ceria (111) surface. In other words, reoxidation of the reduced ceria (111) surface through the dissociation of the hydroxyl surface and the generation of H_2 molecules is an endothermic process. Therefore, there are mainly two adsorption states for water molecules on the reduced ceria (111) surface: ⅰ)chemisor ption through a non-H-bond configuration andⅱ) dissociative adsorption with a hydroxyl surface. The hydroxyl surface may dissociate under certain conditions and reoxidize the reduced ceria (111) surface.%采用引入Hubbard参数U 修正的密度泛函理论(DFT+U)方法,对水分子在二氧化铈(111)表面的吸附作用。

铜铈改性镁铝尖晶石作为助催化剂同时脱除FCC烟气中的SOx,NOx

CHEMICAL INDUSTRY AND ENGINEERING PROGRESS 2016年第35卷第10期·3190·化工进展铜铈改性镁铝尖晶石作为助催化剂同时脱除FCC烟气中的SO x，NO x皮志鹏，沈本贤，刘纪昌，刘逸锋，赵基钢（华东理工大学化工学院石油加工研究所，上海200237）摘要：为降低催化裂化烟气中的SO x、NO x，采用溶胶凝胶法合成了Mg-Al尖晶石，并通过共胶法进行金属氧化物改性制备得到催化裂化烟气脱硫脱硝助催化剂。

在小型固定床反应装置上考察了铜铈改性以及烟气中O2含量对尖晶石脱硫脱硝性能的影响，并在小型提升管装置上考察了铜铈复合改性后尖晶石同时脱硫脱硝的性能。

结果表明：经铜铈复合改性后的尖晶石脱硫活性最高，40min内仍能保持90.67%的SO2脱除率；含铜尖晶石的脱硝性能最优，450℃后NO转化率达100%。

烟气中O2含量对脱硫有利而对脱硝不利，当O2含量过高时，NO不能有效脱除。

原位红外漫反射分析表明：含铜尖晶石良好的脱硝性能是因为其含有的Cu+对CO优异的吸附性能，O2的影响在于其与CO的反应，导致CO消耗。

提升管装置评价实验结果表明：主风量为0.6m3/h时，CuCe-MgAl 脱硫效率为59.96%，脱硝效率为87.63%。

当主风量为0.8m3/h时，脱硫效果提升至74.50%而失去了脱硝功能。

关键词：烟气；脱硫；脱硝；尖晶石；改性中图分类号：TE 991.1 文献标志码：A 文章编号：1000–6613（2016）10–3190–06DOI：10.16085/j.issn.1000-6613.2016.10.024CuO，CeO2 modified Mg-Al spinel as additives for removal of SO x andNO x from FCC flue gasPI Zhipeng，SHEN Benxian，LIU Jichang，LIU Yifeng，ZHAO Jigang （Research Institute of Petroleum Processing，School of Chemical Engineering，East China University of Science andTechnology，Shanghai 200237，China）Abstract：Mg-Al spinel was synthetized by Sol-Gel method and modified with CuO and CeO2 via co-gelling method，and was further used to remove SO x and NO x from FCC flue gas. The synthetized catalysts were evaluated on a fixed bed reactor and a lab-scale riser fluid catalytic cracking unit by investigating the influence of metal oxides and O2 content. After modified by CuO and CeO2，Mg-Al spinel kept a desulfurization rate of 90.67% after 40 minutes. Cu-containing spinel showed the best NO removal efficiency，and the NO conversion was 100% when the temperature was over 450℃. O2 was favorable to desulfurization but unfavorable to denitrification. DRIFTS analysis indicated that the excellent adsorption of CO on Cu+ was the reason for high denitrification efficiency of Cu-containing spinel. Lab-scale riser FCC unit evaluation showed that when the flow of air into the regenerator was0.6m3/h，CuCe-MgAl showed a desulfurization rate of 59.96% and a denitrification rate of 87.63%；whenthe air flow was 0.8m3/h，desulfurization rate increased to 74.50% but the denitrification disappeared.Key words：fuel gas；desulfurization；denitrification；spinel；modification催化裂化（FCC）是重要的原油二次加工手段之一，中国的FCC加工能力目前已经达到1.5亿收稿日期：2015-12-25；修改稿日期：2016-03-10。

甲烷二氧化碳重整制氢

Research ArticleNi/SiO2Catalyst Prepared with Nickel NitratePrecursor for Combination of CO2Reforming andPartial Oxidation of Methane:Characterization and Deactivation Mechanism InvestigationSufang He,1Lei Zhang,2Suyun He,2Liuye Mo,3Xiaoming Zheng,3Hua Wang,1and Yongming Luo21Research Center for Analysis and Measurement,Kunming University of Science and Technology,Kunming650093,China2Faculty of Environmental Science and Engineering,Kunming University of Science and Technology,Kunming650500,China3Institute of Catalysis,Zhejiang University,Key Lab of Applied Chemistry of Zhejiang Province,Hangzhou310028,ChinaCorrespondence should be addressed to Y ongming Luo;environcatalysis222@Received5August2014;Revised6January2015;Accepted6January2015Academic Editor:Mohamed BououdinaCopyright©2015Sufang He et al.This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use,distribution,and reproduction in any medium,provided the original work is properly cited.The performance of Ni/SiO2catalyst in the process of combination of CO2reforming and partial oxidation of methane to produce syngas was studied.The Ni/SiO2catalysts were prepared by using incipient wetness impregnation method with nickel nitrate as a precursor and characterized by FT-IR,TG-DTA,UV-Raman,XRD,TEM,and H2-TPR.The metal nickel particles with the average size of37.5nm were highly dispersed over the catalyst,while the interaction between nickel particles and SiO2support is relatively weak.The weak NiO-SiO2interaction disappeared after repeating oxidation-reduction-oxidation in the fluidized bed reactor at 700∘C,which resulted in the sintering of metal nickel particles.As a result,a rapid deactivation of the Ni/SiO2catalysts was observed in2.5h reaction on stream.1.IntroductionThe Ni-based catalyst has recently attracted considerable attention due to the plentiful resources of nickel,as well as its low cost and good catalytic performance comparable to those of noble metals for many catalytic reactions,such as hydrogenation of olefins and aromatics[1],methane reforming[2],and water-gas shift reaction[3].Therefore,Ni-based catalyst is believed to be the most appropriate catalyst applied in the industrial process[4–6].It is generally accepted that the catalytic performance of Ni-based catalyst is closely related to several parameters,including the properties of support,preparation method,and active phase precursor employed.Support plays an important role in determining the performance of Ni-based catalyst.Generally,a support with high surface areas is very necessary since it is effective in increasing Ni dispersion and improving thermal stability, hence not only providing more catalytically active sites,but also decreasing the deactivation over time of the catalysts due to sintering and migration effects[7,8].For its good thermostability,availability,and relative high specific surface area,SiO2support was widely used for preparing Ni-based catalyst[9].In particular,spherical silica is successfully used as a catalyst support in fluidized bed reactor due to its high mechanical strength.The method of catalyst preparation is another key param-eter which needs to be optimized because it will result in different structural and textural properties of Ni-based catalyst.Therefore,numerous methods,including precipi-tation,homogeneous deposition-precipitation,and sol-gel techniques,have been developed to enhance the performance of Ni-based catalyst[10–18].However,allthe above method-ologies mentioned are too complex or expensive to scaleHindawi Publishing Corporation Journal of NanomaterialsVolume 2015, Article ID 659402, 8 pages /10.1155/2015/659402up in industry.The incipient wetness impregnation(IWI) is one of the most extensively used method[19–23]due to its simplicity in practical execution on both laboratory and industrial scales,in addition to its facility in controlling the loading amount of the active ingredient.In addition,the choice of the precursor salt is also crucial since it determines whether the Ni-based catalyst will be prepared successfully or not.As an efficient precursor,two terms must be met:firstly,high solubility is desirable because the precursor concentration in the impregnation solution must be high[24];secondly,the ability to be decomposed during calcinations is prerequisite since the precursor must be fully transformed into oxide particles without leaving side species that may modify the properties of the support [24].As a result,owing to its commercial availability and low cost,as well as its high solubility in water and effortless decomposition at moderate temperatures,nickel nitrate is the precursor most often used in the preparation of Ni-based catalyst[23,24].In this paper,Ni/SiO2catalyst was prepared by incipient wetness impregnation(IWI)with nickel nitrate as precursor and tested in the process of combination of CO2reforming and partial oxidation of methane(CRPOM)to produce syngas.TG-DTA,HR-TEM,IR,UV-Raman,XRD,and H2-TPR were employed to characterize the Ni/SiO2catalysts in detail to reveal the relationship between synthesis,properties, and catalytic performances as well as to investigate the causes of deactivation.2.Experimental Section2.1.Catalyst Preparation.The Ni/SiO2catalysts were pre-pared with IWI using nickel nitrate as precursor according to our previous works[21,22].The SiO2was commer-cially obtained(S BET=498.8m2/g,Nanjing Tianyi Inorganic Chemical Factory).Prior to use,the SiO2was pretreated with5%HNO3aqueous solution for48h and then washed with deionized water until the filtrate was neutrality.The size of SiO2was selected between60and80mesh.It was then impregnated with an aqueous solution of nickel nitrate. The obtained sample was dried overnight at100∘C and subsequently calcined in air at700∘C for4h.Unless otherwise stated,the loading of Ni was3wt%,and the calcination temperature was700∘C.The Ni/SiO2catalyst was designated as3NiSN.2.2.Catalytic Reaction.The catalytic reaction was performed in a fluidized-bed reactor that was comprised of a quartz tube (I.D.=20mm,H=750mm)under atmospheric pressure at700∘C.Prior to reaction,2mL of catalyst was reduced at700∘C for60min under a flow of pure hydrogen at atmospheric pressure with a flow rate of50mL/min.A reactant gas stream that consisted of CH4,CO2,and O2,with a molar ratio of1/0.4/0.3,was used with a gas hourly space velocity(GHSV)of9000h−1.The feed gas was controlled by mass flow controllers.The effluent gas cooled in an ice trap was analyzed with an online gas chromatograph that was equipped with a packed column(TDX-01)and a thermal conductivity detector.Under our reaction conditions,the oxygen in the feed gas was completely consumed in all cases.2.3.Catalyst Characterization.FTIR spectra were measured using a Nicolet560spectrometer equipped with a MCT detector.The samples were tabletted to thin discs with KBr.Thermogravimetric analysis(TGA)and differential ther-mal analysis(DTA)were performed on a PERKIN ELMER-TAC7/DX with a heating rate of10∘C/min under oxygen (99.99%,20mL/min).The samples were pretreated with oxygen flow at383K for1h.UV-Raman spectra were carried out with a Jobin Yvon LabRam-HR800instrument,using325.0nm Ar+laser radi-ation.The excitation laser was focused down into a round spot approximately2μm in diameter.The resolution was 4cm−1and1000scans were recorded for every spectrum.The catalysts were ground to particle diameters<150μm before analysis.X-ray powder diffraction(XRD)patterns of samples were obtained with an automated power X-ray diffractometer (Rigku-D/max-2550/PC,Japan)equipped with a computer for data acquisition and analysis,using Cu Kαradiation, at40kV and300mA.The reduced samples were priorly reduced at700∘C for1h and cooled to room temperature in hydrogen atmosphere,but the fresh samples were used directly after calcined in air at700∘C for4h.All the samples were ground to fine powder in an agate mortar before XRD measurements.Transmission electron microscopy(TEM)images were recorded on a Philips-FEI transmission electron microscope (Tecnai G2F30S-Twin,Netherlands),operating at300kV. Samples were mounted on a copper grid-supported carbon film by placing a few droplets of ultrasonically dispersed suspension of samples in ethanol on the grid,followed by drying at ambient conditions.H2-temperature-programmed reduction(H2-TPR) experiments were performed in a fixed-bed reactor(I.D.= 4mm).50mg samples were used and reduced under a stream of5%H2/N2(20mL/min)from50∘C to800∘C with a ramp of7∘C/min.Hydrogen consumption of the TPR was detected by a TCD and its signal was transmitted to a personal computer.The experiments for reduction-oxidation cycle(redox) performance were performed as follows.The catalysts were pretreated with H2flow at700∘C for1h and then were cooled down to room temperature and reoxidized in O2at different temperature for1h.The reoxidized samples were then performed by H2-TPR experiments as above.3.Results and Discussion3.1.Catalytic Activity Measurements.The catalytic perfor-mance of Ni/SiO2was shown in Figure1.A rapid deactivation was detected for the3NiSN,and the corresponding conver-sion of CH4(X CH4)decreased from∼58%to∼25%within 1.5h reaction on stream.In order to investigate the causes of deactivation,the3NiSN catalyst was characterized by TG-DTA,HR-TEM,IR,UV-Raman,XRD,and H2-TPR in detail.Time on stream (h)60555045403530252015C o n v e r s i o n o f C H 4(%)Figure 1:CH 4conversion versus time on 3NiSN catalyst for combination of CO 2reforming and partial oxidation of methane to produce syngas (reaction temperature:700∘C,CH 4/CO 2/O 2=1/0.4/0.3,and GHSV =9000h −1).Wavenumber (nm)Figure 2:FT-IR spectra of 3NiSN (dried at 100∘C)and nickel nitrate (Ni(NO 3)2).3.2.Catalyst Characterization Results3.2.1.FT-IR Analysis.The FT-IR spectra of 3NiSN before cal-cination and Ni(NO 3)2precursor were illustrated in Figure 2.Two intense bands of Ni(NO 3)2centered at 1620cm −1and 1376cm −1were ascribed to asymmetric and symmetric vibra-tions of nitrate,respectively [25].After Ni(NO 3)2being impregnated on SiO 2,the position of the two bands of Ni(NO 3)2shifted to higher wavenumber about 1643cm −1and1385cm −1,respectively.Similar to our previous study [23],this shift to higher wavenumber might be contributed to the interaction between nickel nitrate and support SiO 2.3.2.2.Thermal Analysis.In order to study the formation of NiO from precursor,thermal analysis of 3NiSN before calcination was carried out (shown in Figure 3).The extra water should be removed by holding the precursor under O 2at 110∘C for 1h.The thermal oxidation degradation of the dried 3NiSN consisted of two main steps.The first weight loss (9.1wt%)at 110–240∘C region in TG together with a differential peak at around 224∘C in DTG curve was probably due to the dehydration of 3NiSN.The second large weight loss at region of 240–380∘C (11.1wt%)in TG,accompanied with a small endothermic peak around 293∘C in DTA,had been attributed to thermoxidative degradation of nickel nitrate.This decomposition step exhibited a differential peak around 277∘C in DTG profile.Above 380∘C,practically weight loss could not be observed any more.The TG-DTA curves confirmed the absolute volatility of water and nitrate and also the formation of NiO over catalysts around 380∘C.The calcination of 3NiSN beyond 380∘C would enhance the interaction between the NiO and SiO 2support,according to our earlier study [23].3.2.3.UV-Raman Analysis.Further evidence for the for-mation of NiO might be drawn from UV-Raman spectra exhibited in Figure 3.Herein,the spectrum for NiO was included as a reference.As seen from Figure 4,the intense and sharp peak at 1139cm −1,together with three weak peaks at 900,732,and 578cm −1,was assigned to the Raman responses of NiO.Similar to NiO reference,the peaks of 3NiSN center at about 1135,900,726,and 580cm −1were also attributed to NiO.Furthermore,compared with the reference of NiO,the four Raman peaks of NiO over 3NiSC appeared more intensive,thus suggesting that the NiO particles over 3NiSN catalyst were larger [23,26,27].3.2.4.XRD Analysis.XRD measurements were carried out to understand the crystalline structure of 3NiSN catalysts,and the results were presented in Figure5.The XRD patterns of all samples exhibited a broad and large peak around 22∘,which was attributed to amorphous silica of support.After calcination,the sample showed only the fcc-NiO phase,with typical reflections of the (111),(200),and (220)planes at 2θ=37∘,43∘,63∘,respectively.After being reduced with H 2for 4h,the peaks assigned to NiO disappeared,and three other peaks around 44∘,52∘,and 76∘for Ni (111),Ni (200),and Ni (220)planes were detected,thus inferring the successful transformation of NiO to metallic Ni after reduction with H 2.3.2.5.TEM Analysis.Further insight on the aggregation of Ni particles over the 3NiSN could be obtained by TEM analysis.Figures 6(a)and 6(b)exhibited the TEM images of 3NiSN after reduction and deactivation,respectively.The Ni particles over both catalysts were approximately spherical in shape.Highly dispersed Ni particles were detected for the Ni/SiO 2just after reduction.However,obvious glomeration200300400500600700Temperature (∘C)T G +D T G(a)200300400500600700Temperature (D T A∘C)(b)Figure 3:(a)TG +DTG and (b)DTA thermogram of 3NiSN dried at 100∘C.Raman shift (cm −1)I n t e n s i t y (a .u .)Figure 4:UV-Raman spectra of 3NiSN (calcined at 700∘C for 4h)and NiO (as a reference).of Ni particles was observed for the 3NiSN catalyst after deactivation.In order to make a profound analysis,the corresponding particle size distributions obtained from TEM were summarized in Figures 6(c)and 6(d)for 3NiSN after reduction and deactivation,respectively.The particle size values of reduced 3NiSN were distributed in a range of 16.1–84.0nm with the average size around 37.5nm.As for 3NiSN after deactivation,the mean size increased to 50.4nm2θ(deg)Ni NiOI n t e n s i t y (a .u .)Figure 5:XRD patterns of 3NiSN before and after reduction in H 2for 4h.with distributed range of 36.0–73.6nm.An evident particle aggregation was formed over 3NiSN catalyst,which was in accordance with the XRD result.3.2.6.H 2-TPR Analysis.TPR is an efficient method to char-acterize the reducibility of supported nickel-based catalysts.(a)(b)Particle diameter (nm)0.250.200.150.100.050.00R e l a t i v e p a r t i c l e n u m b e r (%)(c)0.200.150.100.050.00R e l a t i v e p a r t i c l e n u m b e r (%)Particle diameter (nm)(d)Figure 6:TEM images of (a)reduced 3NiSN and (b)deactivated 3NiSN,and histogram of the particle size distribution obtained from sampling of nanoparticles from TEM data (c)for reduced 3NiSN and (d)for deactivated 3NiSN.TPR profiles of 3NiSN catalysts were depicted in Figure 7.Two reduction peaks were observed for the fresh 3NiSN cata-lyst (just calcined)at 430∘C and 450∘C.The low-temperature peak might be contributed to the reduction of NiO which is negligible weak interaction with SiO 2.The high-temperature peak was caused by the reduction of nickel oxide which interacted weakly with SiO 2.Furthermore,ttthe reduction-oxidation cycle (redox)performance of a catalyst would strongly influence the catalytic activity for an oxidation involved reaction [28].Therefore,the redox performances of 3NiSN catalysts were investigated,and the corresponding experiment results were depicted in Figure 7.After beingreduced in H 2flow at 700∘C for 1h,the 3NiSN catalysts were reoxidized in O 2at different temperatures and then tested with H 2-TPR.No clear reduction peak of NiO was detected for 3NiSN with reoxidized temperature below 300∘C.As reoxidization temperature increased from 400to 700∘C,the rereduction temperature increased from ∼290to ∼370∘C;however,it was always less than the temperature needed to reduce the NiO of fresh 3NiSN.Distinctly,the weak NiO-SiO 2interaction over 3NiSN catalyst disappeared with repeat-ing oxidation-reduction-oxidation process.Studies from the previous work show that the strong interaction between NiO and support could suppress efficiently the sintering of200300400500600Temperature (FED C B A∘C)H 2c o n s u m p t i o n (a .u .)Figure 7:The reduction-oxidation cycle (redox)performance of 3NiSN catalysts with different reoxidization temperature (A:300∘C;B:400∘C;C:500∘C;D:600∘C;E:700∘C;F:fresh,just calcined).metallic nickel [21–23].Therefore,the disappearance of NiO-SiO 2interaction would lead to the sintering of active nickel particles at high reaction temperature.3.2.7.Effect of the Particle Size of Ni.It is generally accepted that the crystalline size of metallic nickel plays an important role in the catalytic performance for nickel-catalyzed reac-tions:smaller metallic Ni size helps to provide more active sites to reach the much better catalytic activity.Our previous works had also demonstrated this view [21,22].In order to investigate the particle size dependence of the catalytic reaction,the 3NiSN catalysts after different time (1.5h,2.0h,and 2.5h)reaction on stream were taken out to be estimated by XRD and calculated with the Scherrer equation (shown in Figure 8).For all the 3NiSN (even after deactivation),only Ni and amorphous SiO 2phase detected by XRD.No NiO phase was found,which meant no significant change in Ni phase was observed for 3NiSN even after deactivation.Noteworthily,the diffraction intensity of nickel crystalline increased with reaction time,which indicated the crystalline size of nickel on 3NiSN increased with reaction time.The crystalline size of nickel on 3NiSN as a function of reaction time was shown in Figure 9.The crystalline size of nickel was ∼30.3nm,∼32.6nm,∼33.6nm,and ∼34.6nm,for 3NiSN after 0h,1.5h,2h,and 2.5h reaction on stream,respectively.The change trend of Ni size was in conformance with the catalytic activity of 3NiSN in process of bined with H 2-TPR results above,with the process of CRPOM proceeding,the NiO-SiO 2interaction over 3NiSN catalyst weakened down as it disappeared.At the same time,the crystalline size of nickel increased with the weakening of NiO-SiO 2interaction,finally leading to the sintering of active nickel particles over 3NiSNcatalyst.2θ(deg)NiI n t e n s i t y (a .u .)Figure 8:The effect of reaction time on the XRD patterns of3NiSN.Reaction time (h)353433323130C r y s t a l l i n e s i z e o f n i c k e l (n m )Figure 9:Crystalline size of nickel as a function of reaction time.By comprehensively analyzing the characterization results,important information could be concluded.On one hand,graphic carbon was not detected in the spent 3NiSN catalyst by XRD and TEM,suggesting that no carbon deposition was formed during the reaction.On the other hand,except for the characteristic XRD peak of metallic nickel,no other nickel species (such as NiO)was detected,indicating that the transformation of active metallic Ni was not the reason for deactivation of 3NiSN.Importantly,the weak interaction between Ni and support disappeared asthe reaction proceeding,resulting in sintering of active nickel particles.This was the reason that3NiSN catalyst showed a rapid deactivation in the CRPOM reaction.4.ConclusionsIn this work,Ni/SiO2catalysts were prepared with nickel nitrate precursor by IWI method and characterized by FT-IR,TG-DTA,UV-Raman,XRD,TEM,and H2-TPR.By being calcined around380∘C,water and nitrate were volatilized absolutely to form NiO,which could be reduced into metallic Ni after being treated with H2at700∘C.The active nickel particles(around37.5nm)of3NiSN catalyst were dispersed highly but weakly interacted with SiO2support.However, this weak interaction disappeared after repeating oxidation-reduction-oxidation in the fluidized bed reactor at700∘C. Therefore,3NiSN catalyst suffered from obvious sintering of the active nickel particle.In light of these,a rapid deactivation of3NiSN was shown in the process of combination of CO2 reforming and partial oxidation of methane(CRPOM)to produce syngas.Conflict of InterestsThe authors declare that there is no conflict of interests regarding the publication of this paper. AcknowledgmentsThe authors thank the financial supports of National Natural Foundation of China(nos.21003066,21367015,and51068010) and Zhejiang Province Key Science and Technology Innova-tion Team(2012R10014-03).References[1]B.Pawelec,P.Casta˜n o,J.M.Arandes et al.,“Katalizatory ni-klowe i rutenowo-niklowe na no´s nikach zawierających zeolit ZSM-5i tlenek glinu.Wybrane wła´s ciwo´s ci fizykochemiczne i katalityczne,”Applied Catalysis A:General,vol.7,no.7,pp.20–33,2007.[2]T.V.Choudhary and V.R.Choudhary,“Energy-efficient syngasproduction through catalytic oxy-methane reforming reac-tions,”Angewandte Chemie,vol.47,no.10,pp.1828–1847,2008.[3]K.-R.Hwang,S.-W.Lee,S.-K.Ryi,D.-K.Kim,T.-H.Kim,and J.-S.Park,“Water-gas shift reaction in a plate-type Pd-membrane reactor over a nickel metal catalyst,”Fuel Processing Technology, vol.106,pp.133–140,2013.[4]D.P.Liu,X.-Y.Quek,H.H.A.Wah,G.M.Zeng,Y.D.Li,andY.H.Yang,“Carbon dioxide reforming of methane over nickel-grafted SBA-15and MCM-41catalysts,”Catalysis Today,vol.148, no.3-4,pp.243–250,2009.[5]V.R.Choudhary,B.S.Uphade,and A.S.Mamman,“Partialoxidation of methane to syngas with or without simultaneous CO2and steam reforming reactions over Ni/AlPO4,”Microp-orous and Mesoporous Materials,vol.23,no.1-2,pp.61–66,1998.[6]E.Ruckenstein and Y.H.Hu,“Combination of CO2reformingand partial oxidation of methane over NiO/MgO solid solution catalysts,”Industrial and Engineering Chemistry Research,vol.37,no.5,pp.1744–1747,1998.[7]J.Newnham,K.Mantri,M.H.Amin,J.Tardio,and S.K.Bhargava,“Highly stable and active Ni-mesoporous alumina catalysts for dry reforming of methane,”International Journal of Hydrogen Energy,vol.37,no.2,pp.1454–1464,2012.[8]M.Garc´ıa-Di´e guez,I.S.Pieta,M.C.Herrera,rrubia,and L.J.Alemany,“Nanostructured Pt-and Ni-based catalysts for CO2-reforming of methane,”Journal of Catalysis,vol.270, no.1,pp.136–145,2010.[9]L.Yao,J.Zhu,X.Peng,D.Tong,and C.Hu,“Comparative studyon the promotion effect of Mn and Zr on the stability of Ni/SiO2 catalyst for CO2reforming of methane,”International Journal of Hydrogen Energy,vol.38,no.18,pp.7268–7279,2013.[10]S.Tada,T.Shimizu,H.Kameyama,T.Haneda,and R.Kikuchi,“Ni/CeO2catalysts with high CO2methanation activity and high CH4selectivity at low temperatures,”International Journal of Hydrogen Energy,vol.37,no.7,pp.5527–5531,2012.[11]I.Rossetti,C.Biffi,C.L.Bianchi et al.,“Ni/SiO2and Ni/ZrO2catalysts for the steam reforming of ethanol,”Applied Catalysis B:Environmental,vol.117-118,pp.384–396,2012.[12]X.L.Yan,Y.Liu,B.R.Zhao,Y.Wang,and C.-J.Liu,“Enhancedsulfur resistance of Ni/SiO2catalyst for methanation via the plasma decomposition of nickel precursor,”Physical Chemistry Chemical Physics,vol.15,no.29,pp.12132–12138,2013. [13]W.S.Xia,Y.H.Hou,G.Chang,W.Z.Weng,G.-B.Han,and H.-L.Wan,“Partial oxidation of methane into syngas(H2+CO) over effective high-dispersed Ni/SiO2catalysts synthesized by a sol-gel method,”International Journal of Hydrogen Energy,vol.37,no.10,pp.8343–8353,2012.[14]L.Li,S.He,Y.Song,J.Zhao,W.Ji,and C.-T.Au,“Fine-tunable Ni@porous silica core-shell nanocatalysts:synthesis, characterization,and catalytic properties in partial oxidation of methane to syngas,”Journal of Catalysis,vol.288,pp.54–64, 2012.[15]D.P.Liu,Y.F.Wang,D.M.Shi et al.,“Methane reformingwith carbon dioxide over a Ni/ZiO2-SiO2catalyst:influence of pretreatment gas atmospheres,”International Journal of Hydrogen Energy,vol.37,no.13,pp.10135–10144,2012. [16]M.V.Bykova,D.Y.Ermakov,V.V.Kaichev et al.,“Ni-based sol-gel catalysts as promising systems for crude bio-oil upgrading:guaiacol hydrodeoxygenation study,”Applied Catalysis B:Environmental,vol.113-114,pp.296–307,2012. [17]M.Xue,S.Hu,H.Chen,Y.Fu,and J.Shen,“Preparationof highly loaded and dispersed Ni/SiO2catalysts,”Catalysis Communications,vol.12,no.5,pp.332–336,2011.[18]R.Nares,J.Ram´ırez,A.Guti´e rrez-Alejandre,and R.Cuevas,“Characterization and hydrogenation activity of Ni/Si(Al)—MCM-41catalysts prepared by deposition-precipitation,”Indus-trial and Engineering Chemistry Research,vol.48,no.3,pp.1154–1162,2009.[19]A.Corma,A.Martinez,V.Martinezsoria,and J.B.Monton,“Hydrocracking of vacuum gasoil on the novel mesoporous MCM-41aluminosilicate catalyst,”Journal of Catalysis,vol.153, no.1,pp.25–31,1995.[20]T.Halachev,R.Nava,and L.Dimitrov,“Catalytic activityof(P)NiMo/Ti-HMS and(P)NiW/Ti-HMS catalysts in the hydrogenation of naphthalene,”Applied Catalysis A:General, vol.169,no.1,pp.111–117,1998.[21]S.He,H.Wu,W.Yu,L.Mo,H.Lou,and X.Zheng,“Combi-nation of CO2reforming and partial oxidation of methane to produce syngas over Ni/SiO2and Ni–Al2O3/SiO2catalysts with different precursors,”International Journal of Hydrogen Energy, vol.34,no.2,pp.839–843,2009.[22]S.F.He,Q.S.Jing,W.J.Yu,L.Y.Mo,H.Lou,and X.M.Zheng,“Combination of CO2reforming and partial oxidation of methane to produce syngas over Ni/SiO2prepared with nickel citrate precursor,”Catalysis Today,vol.148,no.1-2,pp.130–133,2010.[23]S.He,X.Zheng,L.Mo,W.Yu,H.Wang,and Y.Luo,“Characterization and catalytic properties of Ni/SiO2catalysts prepared with nickel citrate as precursor,”Materials Research Bulletin,vol.49,pp.108–113,2014.[24]E.Marceau,M.Che,J.ˇCejka,and A.Zukal,“Nickel(II)nitrate vs.acetate:influence of the precursor on the structure and reducibility of Ni/MCM-41and Ni/Al-MCM-41catalysts,”ChemCatChem,vol.2,no.4,pp.413–422,2010.[25]J.Chen and Q.Z.Song,Organic Spectral Analysis,BIT Press,Beijing,China,1996.[26]J.F.Xu,W.Ji,Z.X.Shen et al.,“Raman spectra of CuOnanocrystals,”Journal of Raman Spectroscopy,vol.30,no.5,pp.413–415,1999.[27]H.Richter,Z.P.Wang,and L.Ley,“The one phonon Ramanspectrum in microcrystalline silicon,”Solid State Communica-tions,vol.39,no.5,pp.625–629,1981.[28]Z.Zhao,Y.Yamada,A.Ueda,H.Sakurai,and T.Kobayashi,“The roles of redox and acid-base properties of silica-supported vanadia catalysts in the selective oxidation of ethane,”Catalysis Today,vol.93–95,pp.163–171,2004.Scientifica Corrosion Polymer ScienceCeramics Composites Nanoparticles International Journal of Biomaterials Nanoscience TextilesJournal of Nanotechnology Crystallography The Scientific World Journal Coatings Advances in Materials Science and Engineering S mart MaterialsResearch Metallurgy Journal ofBioMed Research International Materials Journal of Journal ofNanomaterials。

尖晶石型铝酸盐光催化还原CO2

尖晶石型铝酸盐光催化还原CO2王剑波;李井芳;陶灿;王玉丰;杜颖;祝现礼【摘要】采用有机物前驱法制备了3种尖晶石型铝酸盐催化剂(CoAl2O4,ZnA12O4,CuA12O4).采用FTIR,XRD, UV-Vis DRS等技术对催化剂进行表征,并将催化剂应用于CO2的光催化还原.表征结果显示:除CuAl2O4外,CoAl2O4和ZnAl2O4在煅烧时均直接形成尖晶石相;CoAl2O4,CuAl2O4,ZnAl2O4的平均粒径分别为25.21,21.35,23.26 nm,禁带宽度分别为1.77,1.45,3.82 eV.分别以煅烧温度为900 ℃、煅烧时间为4h时制得的ZnAl2O4,CoAl2O4,CuAl2O4为催化剂,在催化剂加入量为1.5 g/L、CO2流量为200 mL/min、反应温度为60 ℃的条件下光催化反应8h,甲酸产生量分别为443.54,365.65,241.39 μmol/g.【期刊名称】《化工环保》【年(卷),期】2015(035)005【总页数】5页(P542-546)【关键词】尖晶石型铝酸盐;光催化;二氧化碳;还原【作者】王剑波;李井芳;陶灿;王玉丰;杜颖;祝现礼【作者单位】安徽理工大学化工学院,安徽淮南232001;安徽理工大学化工学院,安徽淮南232001;安徽理工大学化工学院,安徽淮南232001;安徽理工大学化工学院,安徽淮南232001;安徽理工大学化工学院,安徽淮南232001;安徽理工大学化工学院,安徽淮南232001【正文语种】中文【中图分类】TQ034因化石燃料的燃烧生成大量CO2所导致的全球温室效应和过度使用化石原料而导致的能源枯竭问题引起了广泛的关注。

光催化还原CO2技术的出现有望缓解温室效应，并实现碳资源的循环利用。

1979年，Inoue等［1］首先研究了利用粉末状半导体催化剂光电催化CO2和水，生产甲酸、甲醛、甲醇和甲烷。

其中，研究制备的催化剂有TiO2，ZnO，CdS，GaP，SiC，WO3。

1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。

CHIN.PHYS.LETT.Vol.25,No.9(2008)3364AdsorptionandReactionofCOon(100)SurfaceofSrTiO3byDensityFunctionTheoryCalculation∗

YUNJiang-Ni(󰀁󰀁󰀁)1∗∗,ZHANGZhi-Yong(󰀁󰀁󰀁)1,ZHANGFu-Chun(󰀁󰀁󰀁)21SchoolofInformationScienceandTechnology,NorthwestUniversity,Xi’an710127

2Xi’anInstituteofOpticsandPrecisionMechanics,ChineseAcademyofSciences,Xi’an710068

(Received26April2008)AdsorptionandreactionofCOontwopossibleterminationsofSrTiO3(100)surfaceareinvestigatedbytheﬁrst-principlescalculationofplanewaveultrasoftpseudopotentialbasedonthedensityfunctiontheory.Theadsorptionenergy,Mullikenpopulationanalysis,densityofstates(DOS)andelectronicdensitydiﬀerenceofCOonSrTiO3(100)surface,whichhaveneverbeeninvestigatedbeforeasfarasweknowareperformed.ThecalculatedresultsrevealthattheTi-COorientationisthemoststableconﬁgurationandtheadsorptionenergy(0.449eV)isquitesmall.COmoleculesadsorbweaklyontheSrTiO3(100)surface,thereispredominantlyelectrostaticattractionbetweenCOandthesurfaceratherthanachemicalbondingmechanism.

PACS:71.15.Mb,71.20.−b,73.20.AtCarbonmonoxide(CO),whichisreleasedbycarexhaustsasaresultofincompletecombustion,hasbeenoneofthemostdangerousenvironmentalcon-taminationsandharmstohumanbeingbadly.ABO3perovskitesareactivecatalystsforoxidationofCOandmethane,hydrogenationandhydrogenolysisofhydrocarbons,NOreduction,photolysisofwater,etc.[1,2]Amongtheperovskites,SrTiO3exhibitsthetypicalcubicstructureofperovskiteatroomtempera-tureandhighertemperature,anditisaperfectmodelofstudyingtheinteractionbetweenCOandperovskitesurfaces.Toourknowledge,the(100)surfacesofSrTiO3havebeenextensivelystudiedbyvariousexperimen-talandtheoreticalmethods.[3−6]However,thestudyofCOadsorptiononSrTiO3surfaceisrareandtherehasbeennotheoreticalinvestigationonitsofar.Sam-inaetal.[7]experimentallyhavereportedthatCOad-sorbsweaklyontheoxidizedSrTiO3anddissociatesalittle.ItisunclearwhySrTiO3hasweakactivitytoCO.Thusitisnecessarytousethedensityfunctiontheory(DFT)toexplorethebondingmechanismofCOwithSrTiO3(100)surface.InthisLetter,weperformtheﬁrstprinciplescalcu-lationtoinvestigatetheinteractionofCOwithSrTiO3(100)surfacebytheCASTEPsoftwarepackage[8]basedonDFTinaslabmodel.Theperiodicboundaryconditionisusedinthecal-culationwiththerepeatedslabmodel.FortheSrO-terminatedsurface,theslabconsistsoffourSrOlayersandthreeTiO2layers,andfortheTiO2-terminatedonetheslabconsistsoffourTiO2layersandthreeSrOlayers.Inboththecases,theslabswithsevenlatticeconstantthicknessinthesurfaceperpendiculardirectionareseparatedbyafourlatticeconstantvac-uumregion.TwodiﬀerentCOcoverages,p(1×1)andp(2×1)conﬁgurations,correspondingtoadsorptionof1MLand0.5MLofCOhavebeenconsidered.Figure1displaystheadsorptiongeometries,p(2×1)conﬁg-urations,examinedforCOonSrTiO3(100)surface.AllthesevenlayersandCOmoleculeareallowedtofullyrelaxtominimizethetotalenergy.Ourcalculationsareperformedusingtheultra-softpseudopotentialsandthePerdewandWang91parametrizationistakenastheexchangecorrela-tionpotentialinthegeneralizedgradientapproxima-tion(GGA).TheBrillouinzoneintegrationisapproxi-matedbyusingaspecialK-pointssamplingschemeofMonkhorst-Pack.Thecutoﬀenergyofplane-waveissettobe420eVandthe6×6×6and6×6×1K-pointgridsareused,respectively,forbulkand(100)surfaceslab.Eachcalculationisconsideredwhenthemax-imumroot-mean-squareconvergenttoleranceislessthan1×10−5eV/atom.

Fig.1.AdsorptiongeometriesexaminedforCOonSrTiO3(100)surface.

∗SupportedbytheNaturalScienceFoundationofShaanxiProvinceunderGrantNo2005F06.

∗∗Towhomcorrespondenceshouldbeaddressed.Email:yunjiangni821001@sohu.comandzhangzy@nwu.edu.cn

c󰀃2008ChinesePhysicalSocietyandIOPPublishingLtdNo.9YUNJiang-Nietal.3365Beforestartingthesurfacecalculations,weopti-mizeCOmoleculesandthebulkSrTiO3structure.ThecalculatedfreeCObondlengthis1.141˚A.ThecomputedgroundstatestructurallatticeconstantofcubicSrTiO3is3.9104˚A,whichisinagreementwiththeexperimentalresult3.905˚A.[9]Table1displaysthecalculatedMullikenpopulationanalysisforbulkSrTiO3.TheeﬀectivechargeofSr(1.94e)isclosetothe+2formalcharges,whereastheOatomiswith0.8negativechargesandtheTiatomcarries0.48positivecharges,whicharemuchsmallerthantheir−2eand+4eformalcharges,respectively.ThisresultsfromtheTi–OcovalentbondingandSr-Oionicbonding.Thepositiveandnegativevaluesoftheoverlappop-ulationsindicatebondingandantibondingstates,re-spectively.Avaluefortheoverlappopulationclosetozeroindicatesthatthereisnosigniﬁcantinteractionbetweentheelectronicpopulationsofthetwoatoms.Thepositive1.09overlappopulationsofTi–Obondandnegative−0.14overlappopulationsofSr–ObondinTable1havewellconﬁrmedtheaboveresults.Table1.CalculatedMullikenpopulationanalysisforbulkSrTiO3.IonBondOTiSrTi–OSr–OEﬀectivecharge−0.80e0.48e1.94ePopulation1.09−0.14RelaxationsoftheTiO2-andSrO-terminatedsur-facestructuresarelistedinTable2.BoththeTiO2-andSrO-terminatedsurfacesdisplaythereductionofinterlayerdistanced12andexpansionofd23,whichisingoodagreementwiththeLEEDobservation.[6]ThecalculatedsurfacerumplingsfortheTiO2-terminatedsurface(0.085˚A)issmallerthanthatfortheSrO-terminatedsurface(0.203˚A).Experimentalmeasure-mentswithLEED[6]giverumplingsof0.08and0.16˚AfortheTiO2-andSrO-terminatedsurfaces,respec-tively.WhenSrTiO3iscutacross(100)plane,SrlosesmoreOneighboursthanTi(4vs1)andtheSr–Obondshaveahighdegreeofionicity.Therefore,there-laxationoftheSrO-terminatedsurfacealongthe(100)directionislarger.Especially,thelargediﬀerenceintheelectronicchargesofSrandTiobservedinthebulkofSrTiO3ismaintainedinthe(100)surfacesofthismaterial.ForcationsintheSrO-terminatedsur-face,thecalculatedMullikenchargeis1.67e,whereasachargeof0.94eiscalculatedforthecationsintheTiO2-terminatedsurface.ThechargesontheSrandTisurfacecationshaveabigimpactontheadsorbedCOmolecule.