Adsorption and reaction on pristine and oxidized Co–Pd bimetallic particles supported on Al2O3 thin films

A model for bimetallic Co–Pd systems known to be active as Fischer–Tropsch catalysts has been constructed and studied under ultra-high vacuum conditions with respect to its adsorption and reaction properties. It was previously shown that subsequent deposition of Pd and Co results in the formation of core-shell structures; the morphology of the bimetallic particles can be controlled taking advantage of the different nucleation and growth behavior of Pd and Co. In this study, the reactive properties of pristine and oxidized bimetallic Co–Pd particles with O2, CO, D2, C2D4, and C2H4 have been investigated using temperature programmed desorption and reaction spectroscopy. Hydrogen and CO adsorption is facile on the non-oxidized particles, but is severely inhibited on the oxidized particles. Ethylene binds to the non-oxidized particles in π-bonded and di-σ-bonded configurations and dehydrogenates to form ethylidyne. In contrast, on the oxidized particles, only the π-bonded species is formed. To slightly different degrees, the bimetallic or monometallic particles are active for ethylene hydrogenation; the oxidized particles are essentially non-active for ethylene hydrogenation.