Characterization of β-Palladium Hydride Formation in the Lindlar Catalyst and in Carbon-Supported Palladium

The proton dynamics of palladium catalysts on activated carbon, of palladium on calcium carbonate, and of lead-modified palladium on calcium carbonate (the Lindlar-catalyst), hydrogenated in situ to comparable equilibrium pressure, were measured by means of inelastic incoherent neutron scattering. Isolated primary particles of palladium of similar to 3.2 nm size showed a lower degree of formation of beta-phase hydride than 10-15 nm sized aggregates, which were formed from similar to 3.7 nm primary particles of palladium. The addition of lead to the palladium on calcium carbonate in catalysts of identical primary particle size (3.7 nm) and shape caused a decrease in the beta-phase hydride formation by a factor of 2. For the catalyst selectivity in the hydrogenation of triple to double bonds not only the presence of modifiers at the surface but also a reduced, moderated hydrogen storage function is of relevance.