Kinetic Study for Low-temperature SCR of NO with

Kinetic Study for Low-temperature SCR of NO with NH3 over Mn-Ce/Ti02 Catalyst
Yang L· " 1U , L' lao Welpmg
1 1*
' 12 , ang F el '
l. Nanjing Normal University, Nanjing, China, 210042 2. Beijing Lucency enviro-tech co.,LTD. Nanjing Branch, Nanjing, China, 210019 * E-mail: liaowp2005@
B.
Catalytic Activity Measurement
The SCR activity measurement was carried out in a fixed­ bed quartz tube reactor under atmospheric pressure at 333K�433K. The quartz tube reactor was placed 7ml of catalyst. The typical reactant gas composition was: NO of 200�1000 ppm, NH3 of 200�1000 ppm, O2 of 0�18%, and balanced N2. The total flow rate was 400�1400ml/min and the tube of the reactor system was heated to prevent formation and deposition of ammonium nitrate. The reaction temperature was controlled by a programmable temperature controller. NO, N02, and O2 concentrations were monitored by a flue gas analyzer
Abstract-In this paper, the Mn-Ce/Ti02 catalyst prepared by co­
precipitation, study the low temperature performance of selective catalytic reduction (SCR) NO of catalyst within the temperature range 333�433K with NH3 in presence of excess O2, Under ideal conditions, the study shows that when ratio of molar of catalyst Mn/(Mn+Ce) reach to 0.7, low temperature selective catalytic activity of catalyst will be the best. NO will be removal in more than 90% at 393K. Through steady-state kinetic experiments, the reaction of low temperature SCR of Mn-Ce/Ti02 catalyst is found to NO, NH3, O2 reaction order were 1, 0,0.5. By calculating, the activation energy of reaction of Mn-Ce/Ti02 catalyst is 40kJ/mol, which is lower than most of the reported activation energy of the catalyst reaction.
thesis, it was highlighted that the active components and support of the catalyst were precipitated in the mixture solution at the same time. Yang[9] investigated that the catalyst that was prepared by co-precipitation MnOX-Ce02' The co-precipitation method was a better way to obtain SCR catalysts with good amorphous oxides in the structure. Thus, in this paper, the catalyst was prepared by co-precipitation method to achieve higher NO conversion and an experimental of SCR reaction was carried out by using these catalysts. The catalyst great performance on the low-temperature SCR was experimentally studied, though the operating parameters contain catalyst composition, reaction temperature, oxygen concentration and ammonia concentration. Furthermore, apparent activation energy is an important parameter to evaluate the catalytic activity. Also we carried out experiments 0, to calculate the apparent activation energy [1 Ill, which could be used to compare the performance of Mn-Ce/Ti02 with that of other catalysts in low-temperature window. II. A. Catalyst Preparation
Research Projects of GuoDian Science and Technology Research Institute (NO.DlOT02)
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The catalyst was prepared by co-precipitation method. All chemicals used were of analytical grade. The solutions of titanium nitrate were prepared by titanium sulfate, which had been precipitated, filtered, cleaned and dissolved. Then the solutions of manganese nitrate and cerium nitrate were mixed into the solutions. And excess solution of ammonium carbonate was added slowly to the mixture solution with stirring. The mixtures were aged for I h and filtered. The obtained solid sample was first dried at 393K for 12h and then calcined at 773K for 6h in a tubular furnace. Finally, the sample was crushed and sieved to 60�80 mesh. The catalyst is denoted as Mn-Ce/Ti02 (Z). Z represents the molar ratio of Mn/(Mn+Ce). e.g. Mn-Ce/TiOiO.7).
EXPERIMENT
Keywords-low-temperature; co-precipitation; Mn-Ceni02; NO; selective catalytic reduction
I.
INTRODUCTION
Selective catalytic reduction (SCR) of NOx with ammonia is effectively control of the emission of NOx' A large number of materials have been tested as the SCR catalysts. It is a well established commercial technology, which employs V20S/ I, 2 Ti02 or V20s-W03/Ti02 [ ] as catalyst. Recently there is a strong interest in developing the highly active for low­ temperature (373�523K) SCR catalyst. Such catalyst would be placed downstream of the desulfurizer or particulate control device, which most of sulfur dioxide and dust are removed, but the temperature is relatively lower. If such a catalyst is successful developes, it will significantly improve the economics of SCR. Manganese oxides are well known for their activity in low­ temperature SCR, since they contain various types of labile oxygen, which are important to complete the catalytic cycle. 3 Kapteijn[ ] believed that the catalytic activity of pure manganese oxides was determined by the oxidation state of the manganese and the crystallinity. Furthermore, to improve catalytic activity of catalyst, manganese oxides were based on titanium dioxide (Ti02) or other carriers. And Pefie[4] found that the catalytic performance of metal oxides supporting on Ti02 decreased in the following order: Mn>Cu2':Cr2':Co>Fe2':V» > Ni. The activity of the catalyst with the introduction of Ceria investigated by Wu[S], is based on MnO/Ti02[6], and the addition of Ceria could improve the catalyst oxygen storage capacity and facilitate the oxygen mobility over catalysts. In previous literatures, almost all of the catalrsts studied ,8 were prepared by solution impregnation method [7 . But in this