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Abstract

Appropriate reaction selectivity is likely the biggest issue on the way to economically feasible industrial catalytic processes. Palladium particles are able to add one hydrogen molecule to both alkenes and alkynes, hence the question may arise how the catalyst prohibits total hydrogenation of alkynes and multiple unsaturated hydrocarbon. We investigated the hydrogenation of various alkenes and alkynes on palladium catalysts by catalytic reaction and high-pressure XPS experiments, and found that the active surface of selective alkyne hydrogenation consist of a Pd-C surface phase. Carbon embedded in the palladium lattice inhibits the emergence of bulk-dissolved hydrogen to the surface, which is reactive but unselective. Moreover, Pd-C does not build up from alkenes.