Characterization of Surface Structure Evolution in Ni3Al Foil Catalysts by Hard X-ray Photoelectron Spectroscopy

Abstract

We had, in a previous study, found that flat cold-rolled Ni3Al foil is spontaneously activated during the initial stage of catalytic methanol decomposition, and further, this is accompanied by the gradual formation of fine Ni particles. In this study, we investigate the evolution of the foil surface structure at the beginning of the spontaneous activation by using hard X-ray (hv = 5.95 keV) photoelectron spectroscopy. The core level spectra of Ni 2p, Ni 3p, Al 2p, O 1s, Al 1s, and C 1s have been analyzed in detail. Ni in the Ni3Al foil remained in the metallic state during the reaction, and neither Ni oxide nor Ni hydroxide was formed. In contrast, Al was found to react with the gaseous products of methanol decomposition to form two compounds in succession. At the beginning of the reaction, Al was oxidized to form an Al2O3 layer on the surface. The outer surface of the Al2O3 layer then hydroxylated to Al(OH)(3), thereby forming an Al(OH)(3)/Al2O3 two-layer structure. Thus, it was found that an Al(OH)(3)/Al2O3 two-layer structure with metallic Ni particles evolves during the initial stage of catalytic methanol decomposition.