Structure and catalytic activity of alumina-supported platinum-cobalt bimetallic catalysts. 2. Chemisorption and catalytic reactions

Abstract

A series of Pt{sub 1{minus}x}Co{sub x}/Al{sub 2}O{sub 3} bimetallic catalysts have been characterized by temperature-programmed reduction (TPR), chemisorption of hydrogen and CO, deuterium exchange using both methanol and methane, and activity for the CO/H{sub 2} reaction. A Pt-assisted reduction mechanism over the entire range of composition was established by the TPR studies as well as by the chemisorption results. An enhanced metallic dispersion for the Pt-rich catalyst and formation of bimetallic particles on the Co-rich side was also indicated. In the CO hydrogenation over the Pt-rich catalysts the predominant products are methanol and dimethyl ether whereas on the Co-rich samples hydrocarbons and higher alcohols are produced. The mechanisms of deuterium exchange with methane and methanol are significantly different, the former being catalyzed solely by metallic sites while the latter utilizes both oxide and metallic sites for stepwise and multiple exchange, respectively. On the basis of the XPS data (preceding article) as well as the chemisorption results reported here, a surface model is introduced for interpretation of the catalytic results.