CHROMIA ON SILICA AND ALUMINA CATALYSTS - CHROMIA DISPERSION AS DETERMINED BY N-2-ADSORPTION MEASUREMENTS

Silica- and alumina-supported chromia catalysts at loadings varying between 0.5 and 10 mole % Cr2O3 were prepared from different parent compounds and characterized by N2-adsorption at 77 K. The adsorption isotherms were evaluated on the basis of the BET- and alpha(s)-methods. The results suggest that the chromia exists on the surface of silica with rather low dispersion probably in the form of small Cr2O3 crystallites which lead to pore blocking. In contrast, on alumina narrowing of pores is observed, this being suggestive of formation of a highly dispersed chromia layer. These conclusions can be rationalized on the basis of the different surface chemical properties of the oxide supports, and they are consistent with previously reported spectroscopic characterizations of the same materials. It is inferred that in fact N2-adsorption data do provide valuable qualitative information on the dispersion of supported oxide materials.