PLATINUM-CATALYZED OXIDATION OF ALCOHOLS IN AQUEOUS-SOLUTIONS - THE ROLE OF BI-PROMOTION IN SUPPRESSION OF CATALYST DEACTIVATION

Deactivation of Pt/alumina during the selective oxidation of primary and secondary alcohols to carbonyl compounds or acids has been studied and an overview is given on the influence of promotion with Pi. The o;uidation state of bimetallic catalysts was measured electrochemically during the reaction. The three main reasons of deactivation are the self-poisoning of Pt due to by-product formation, the over-oxidation of the contaminated active sites and the corrosion of oxidized metals. Only the unpoisoned catalyst is in a reduced state during reaction, as expected from the dehydrogenation mechanism. It is proposed that the dominant influence of Pi-promotion is a geometric (ensemble) effect, which suppresses the formation of CO and CxHy type poisoning species and their strong adsorption on Pt. The superior effect of Bi is likely due to the bigger site requirement of Pi adatoms, compared to other promoters. When the poisoned catalyst is in a partially oxidized state during reaction, the promoter may form new active centers, which adsorb the oxidizing species better than Pt (bifunctional catalysis).