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 ∼3.2 nm size showed a lower degree of formation of β-phase hydride than 10–15 nm sized aggregates, which were formed from ∼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 β-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.