Phenylacetylene hydrogenation with Pd, Pt and Pd-Pt alloy catalysts dispersed on amorphous supports: effect of Pt/Pd ratio on catalytic activity and selectivity

Abstract

Phenylacetylene was hydrogenated using dispersed catalysts of Pd, Pt, and Pd-Pt alloys with different Pd/Pt ratios, in tetrahydrofuran suspension at 25°C and constant H 2 pressure; the same reaction was also carried out using mechanical mixtures of single Pd and Pt catalysts. The catalysts are sufficiently selective for the steps corresponding to the hydrogenation of phenylacetylene to styrene and of styrene to ethylbenzene to appear separated. The Pd-Pt system was studied as a function of the Pd/Pt ratio. Specific catalytic activity for the styrene hydrogenation displays a remarkable increase up to 20–30 at.% of Pt, whereas in the range 30–100 at.% Pt, it corresponds to the sum of the individual Pt and Pd activities; in the case of the hydrogenation of phenylacetylene to styrene, the specific catalytic activity of alloy catalysts is smaller than the sum of individual Pd and Pt in the 10–100 at.% Pt range. These results are discussed and interpreted in terms of the possible destabilizing effect of Pt alloying on the original Pd framework and of the chemical stability of the substrate + hydrogen + metallic surface ensemble. For the Pd-Pt alloy catalysts, the data suggest that the selectivity is independent of the degree of dispersion.