Electrochemical Promotion in Emission Control Catalysis: The Role of Na for the Pt-Catalysed Reduction of NO by Propene

摘要

Conventional heterogeneous metal catalysts are commonly enhanced by the addition of so-called promoter species that are used to midify intrinsic metal surface chemistry with respect to activity and/or selectivity. Electrochemical promotion (EP) provides an in situ, reversible and efficacious means of catalyst promotion and it allows for a systematic study of the role of promoters in heterogeneous catalysis. EP studies relevant to the "three-way" catalytic chemistry i.e., control of automotive CO, NO and hydrocarbons emissions, demonstrate that major enhancements in activity of Pt catalyst supported on a"-Al_2O_3 (a sodium ion conductor) are possible when Na is electrochemically pumped to the catalyst surface. In the case of the important reactions involving NO reduction by CO or by hydrocarbons, major enhancements in selectivity towards N_2 (from 15 to 70percent) have been also achieved. The promotional effect of Na is due to enhanced NO chemisorption and pronounced NO dissociation on the Pt surface.