SPECTROSCOPIC EVIDENCE OF CU-AL INTERACTIONS IN CU-ZN-AL MIXED-OXIDE CATALYSTS USED IN CO HYDROGENATION

Three different Cu-Zn-Al catalysts (Cu:Zn:Al atomic ratio 60:38:2) wer e prepared by coprecipitation of the three metals (from their nitrate salts) either by separately precipitating each metal (Cu + Zn + Al), t wo metals (Cu and Zn coprecipitated + Al) before mixing together, or b y precipitating the three of them together, XPS analysis detected a re markably high Al enrichment at the surface of all calcined or reduced samples, along with a binding energy of the Cu 2p(3/2) core level peak assigned to Cu2+ in CuAl2O4-like environment in the calcined state. E SR spectra of calcined samples showed signals attributed to surface Cu 2+ species with Al entities in their surroundings for samples in which Cu and Zn are coprecipitated and aged together. The higher Cu dispers ion observed after reduction for these catalysts is attributed to the development of such interactions at the surface of Al-containing calci ned samples. (C) 1998 Academic Press.