Liquid phase hydrogenation of phenylacetylene over Pd and PdZn catalysts in toluene: effects of alloying and CO2 pressurization

Abstract

Liquid-phase hydrogenation of phenylacetylene was investigated with Pd and PdZn alloy catalysts in toluene compressed by CO₂. The influence of alloying and dense phase CO₂ on the rate of conversion and the product selectivity was examined. With either Pd or PdZn the partially hydrogenated product of styrene was produced in high selectivity but the selectivity to styrene obtained with the latter was larger than that with the former when compared at the same conversion level. After the initial substrate was fully consumed, the styrene was fully hydrogenated to ethylbenzene for both catalysts but more slowly with the PdZn alloy catalyst. The presence of a dense phase of CO₂ (1.5 MPa) enhanced the rate of phenylacetylene hydrogenation and the selectivity to styrene for the Pd and PdZn catalysts. Possible reasons for the positive effects of alloying and dense phase CO₂ on the partial hydrogenation of phenylacetylene to styrene are discussed.