Effect of sodium on the CoMo/γ-Al2O3 system. Part 1.—Influence of sodium content on the state of dispersion and on the nature of the cobalt supported on γ-Al2O3

Abstract

The effect of sodium content on the dispersion of cobalt on the surface of γ-Al₂O₃ as well as on the type of cobalt species formed on it have been studied using diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, X-ray powder analysis, electron microscopy and thermo-programmed reduction; two series containing, respectively, 2.1 and 8.8 % Co have been investigated.

The former series showed a marked increase in the dispersion of cobalt on the surface of the support, as revealed by X.p.s., when the sodium content increased from 2.3 to 5.7 %. In this composition range, a considerable transformation of Co₃O₄ into CoAl₂O₄, as well as a shift of the distribution of cobalt species from the homogeneous to heterogeneous, have been observed.

In contrast, virtually no change was observed for the 8.8 % Co series throughout the sodium composition range.