IN-SITU CONTROLLED PROMOTION OF CATALYST SURFACES VIA NEMCA - THE EFFECT OF NA ON THE PT-CATALYZED CO OXIDATION

It was found that the catalytic activity of Pt for CO oxidation can be markedly and reversibly affected by depositing polycrystalline Pt fil ms on beta''-Al2O3, a Na+ conductor, and applying external potentials to supply or remove Na to or from the Pt catalyst surface. The change in the rate of CO oxidation is typically 10(3)-10(5) times larger than the rate of supply or removal of Na. The use of the beta''-Al2O3 soli d electrolyte supports permits precise in situ control of the Na cover age on the Pt surface. Sodium coverages of 0.02 cause up to 600% stead y-state increase in the rate of CO oxidation under CO-rich conditions. The promoting effect is due to enhanced oxygen chemisorption on the P t surface. Higher (>0.06) Na coverages poison the rate severely and re versibly due to the formation of a CO-Na-Pt surface complex. Rate osci llations can be reversibly induced or stopped and their frequency can be controlled by controlling the catalyst potential V(WR) and average work function ePHI. (C) 1994 Academic Press, Inc.