ABSTRACT
Abstract The promotional effect of bismuth on heterogeneous platinum catalysts has been studied for the selective oxidation of alcohols to the carbonyl and carboxylic acid functionality. Using either air or hydrogen peroxide as the oxidant it has been shown that effective promotion from bismuth is attained from precipitation onto the catalyst surface and not as an external reaction component. Catalyst activity tests for the selective oxidation of 1 and 2-octanol indicate that the optimal Bi loading for a 5%Pt/carbon catalyst is approximately 1wt.%. Cyclic voltammetry conducted on equivalent 5%Pt/graphite catalysts demonstrate that Bi is preferentially adsorbed onto Pt step and kink sites and that loadings >1wt.% are present mainly as a bulk Bi phase on the catalyst surface. The results of activity tests indicate that the bulk Bi species is an inactive component of the catalyst. Detailed experimental testing using conditions representative of those used in industry reveal that a 5%Pt,1%Bi/C is active for the selective oxidation of a variety of alcohols. The catalyst can be successfully reused for a number of cycles with minimal loss in activity. Introduction The development of clean selective oxidation routes is a challenge to the fine chemical and pharmaceutical industries (1,2). The use of heterogeneous catalysts in conjunction with air or hydrogen peroxide can provide a clean alternative to the use of stoichiometric oxidants (3,4). A potential drawback for this route is premature catalyst deactivation due to either poisoning from the strong adsorption of by-products (5) or the formation of an inactive surface oxide layer (6). An objective in catalyst development is to prepare catalysts having both high activity and stability thereby enabling successful reuse of the catalyst.
