Counting Au catalytic sites for the water-gas shift reaction

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• 作者：Mayank Shekhar ; Jun Wang ; Wen-Sheng Lee ; M. Cem Akatay ; Eric A. Stach ; W. Nicholas Delgass ; Fabio H. Ribeiro
• 关键词：Water&ndash ; gas shift ; Gold ; Bromine poisoning ; WGS kinetics ; Transient isotopic switch ; Operando FTIR
• 刊名：Journal of Catalysis
• 出版年：2012
• 出版时间：September, 2012
• 年：2012
• 卷：293
• 期：Complete
• 页码：94-102
• 全文大小：872 K

文摘

We have developed various techniques to count catalytic sites of Au/TiO₂ catalysts for the water-gas shift (WGS) reaction. Addition of Br in an amount that is only 16 % of the moles of the surface Au on a 2.3 wt. % Au/TiO₂ catalyst decreases the majority of its WGS reaction rate per total mole of Au but does not result in an appreciable change in the average Au particle size, Au particle shape, apparent activation energy, or reaction orders. From transient isotopic switch experiments, the WGS turnover frequency (TOF) for Au/TiO₂ catalysts with and without Br, based on the operating active sites counted in the experiment, is 1.6 ¡À 0.5 s^?1 under 6.8 % CO, 8.5 % CO₂, 11.0 % H₂O, 37.4 % H₂ at 120 ¡ãC. The estimated number of potential active sites, ¡«2 % of the total amount of Au on the 2.3 wt. % Au/TiO₂ catalyst, best correlates with the Au corner atoms (¡«2 % ) of the cubo-octrahedral particles. From operando FTIR spectroscopy, the normalized IR peak area of CO adsorbed on Au⁰ near 2100 cm^?1 is proportional to the WGS reaction rate for Au/TiO₂ catalysts with and without Br. Thus, the dominant active sites on Au/TiO₂ catalysts for the WGS reaction are taken to be the metallic corner Au sites with Au-Au coordination number of 4.