On the activation of Pt/Al<sub>2sub>O<sub>3sub> catalysts in HC-SCR by sintering: determination of redox-active sites using Multitrack
- 作者：Vaccaro ; A.R. ; Mul ; G. ; Pí ; rez ; J. ; Moulijn ; J.A.
- 关键词：Pt ; Al<sub>2sub>O<sub>3sub> ; Sintering ; TAP reactor ; Active site ; Oxidation ; Reduction ; NO<sub>xsub> ; HC-SCR ; Activation
- 刊名：Applied Catalysis B ; Environmental
- 出版年：2003
- 期刊代码：4_09263373
- 类别：ce
- 出版时间：December 15, 2003
- 卷：46
- 期：4
- 页码：687-702
- 文件大小：653 K
摘要
A highly dispersed Pt/Al<sub>2sub>O<sub>3sub> catalyst was used for the selective catalytic reduction of NO<sub>xsub> using propene (HC-SCR). Contact with the reaction gas mixture led to a significant activation of the catalyst at temperatures above 523K. According to CO chemisorption data and HRTEM analysis, Pt particles on the activated catalyst had sintered. The redox behavior of the fresh and sintered catalysts was investigated using Multitrack, a TAP-like pulse reactor. If Pt particles on the catalyst are highly dispersed (average size below 
s/glyphs/BQ1.GIF>2nm), only a small part (s/glyphs/BQ1.GIF>10%) of the total number of Pt surface sites as determined by CO chemisorption (Pt<sub>surfsub>) participates in H<sub>2sub>/O<sub>2sub> redox cycles (Pt<sub>surf,redoxsub>) in Multitrack conditions. For a sintered catalyst, with an average particle size of 2.7nm, the number of Pt<sub>surfsub> and Pt<sub>surf,redoxsub> sites are in good agreement. Similar results were obtained for both catalysts using NO as the oxidant. The low number of Pt<sub>surf,redoxsub> sites on highly dispersed Pt/Al<sub>2sub>O<sub>3sub> is explained by the presence of a kinetically more stable—probably ionic—form of Pts/glyphs/BO7.GIF>O bonds on all surface sites of the smaller Pt particles, including corner, edge and terrace sites. When the average particle size shifts to s/glyphs/BQ1.GIF>2.7nm, the kinetic stability of all Pts/glyphs/BO7.GIF>O bonds is collectively decreased, enabling the participation of all Pt surface sites in the redox cycles.