Influence of bulk composition of the intermetallic compound ZnPd on surface composition and methanol steam reforming properties

Single-phase samples of the intermetallic compound ZnPd, all possessing the CuAu type of crystal struc- ture, were prepared with different bulk compositions and characterized by ICP-OES and XRD. Catalytic experiments in methanol steam reforming in a flow reactor on the unsupported intermetallic compounds proved that Pd-rich catalysts showed limited activity and very low selectivity to CO2, while Zn-rich cat- alysts possessed good activity and CO2 selectivity up to 99.4%. XP spectra of the near-surface region were recorded on as-prepared and reduced samples, showing significant variations in Zn/Pd surface ratios, Pd3d binding energies and the amount of oxidized Zn species on the surface. These properties were cor- related with the Pd content of the bulk compounds. In situ XPS studies revealed that only Zn-rich samples exhibited oxidized Zn species and intermetallic ZnPd on the surface. The catalytic properties correlate strongly with the electronic structure, i.e., the valence band which is determined by the bulk composi- tion. All ZnPd samples still revealed a partially intermetallic near-surface region under MSR conditions