PdZn=Cu: Can an Intermetallic Compound Replace an Element?

Abstract

An intermetallic compound, PdZn, exhibits a similar valence electron density of states as pure Cu, which has been confirmed by energy band calculation and X-ray photoelectron spectroscopy. The catalytic function was verified to be identical for PdZn and Cu. This explains the origin of the high selectivity of PdZn for the steam reforming of methanol (SRM), CH₃OH+H₂O→3H₂+CO₂, a chemical reaction for which Cu is known to be one of the best catalyst; namely, PdZn is catalytically equivalent to Cu. Compared with PdZn, PtZn and NiZn, which have the same crystal structure but different valence band structures, exhibit a poorer selectivity of CO₂. This suggests that the catalytic function, at least for SRM, is solely governed by the valence band structure of the catalyst. A simple but very important principle has been derived that an intermetallic compound may be logically designed by band structure calculation, aiming at replacing a selected metallic element without changing the catalytic function. Using this principle, we designed a compound, PdCd, which exhibits a similar valence electron density of state and selectivity for SRM with Cu.