An in situ EXAFS investigation of bimetallic Cu---Ni/γ-Al₂O₃ catalysts

Abstract

In situ EXAFS investigations have been carried out on Ni/γ-Al₂O₃ and Cu---Ni/γ-Al₂O₃ catalysts with different metal loadings, and prepared by different procedures. As-prepared Ni/γ-Al₂O₃ on calcination gives NiO and NiAl₂O₄-like phases on the surface, the proportion of the latter increasing with the increase in calcination temperature; the proportion of the NiO-like phase, on the other hand, increases with the metal loading. The reducibility of Ni/γ-Al₂O₃ to give metallic Ni on the surface directly depends on the proportion of the NiO-like phase present before reduction. Co-impregnating with Cu suppresses the formation of the surface aluminate and thereby favours the reduction to metallic Ni. This conclusion is clearly substantiated by our studies of bimetallic catalysts containing varying Cu/Ni ratios and also those prepared by the two-stage impregnation procedure.