Spectroscopic Evidence of Cu–Al Interactions in Cu–Zn–Al Mixed Oxide Catalysts Used in CO Hydrogenation

Abstract

Three different Cu–Zn–Al catalysts (Cu : Zn : Al atomic ratio 60 : 38 : 2) were prepared by coprecipitation of the three metals (from their nitrate salts) either by separately precipitating each metal (Cu+Zn+Al), two metals (Cu and Zn coprecipitated+Al) before mixing together, or by precipitating the three of them together. XPS analysis detected a remarkably high Al enrichment at the surface of all calcined or reduced samples, along with a binding energy of the Cu 2p3/2core level peak assigned to Cu2+in CuAl2O4-like environment in the calcined state. ESR spectra of calcined samples showed signals attributed to surface Cu2+species with Al entities in their surroundings for samples in which Cu and Zn are coprecipitated and aged together. The higher Cu dispersion observed after reduction for these catalysts is attributed to the development of such interactions at the surface of Al-containing calcined samples.