Surface composition and catalytic activity of chromia–alumina catalysts

Abstract

The surface composition of chromia–alumina catalysts has been investigated. Electron spin resonance was used to follow changes in the signal ascribed to Cr³⁺ ions (at g= 1.986) after reduction in dry hydrogen (Cr²⁺ produced) and in hydrogen + water-vapour mixture at 500°C (only Cr³⁺ produced). The extent of reduction to Cr²⁺ depends on the concentrations of chromia present on the surface. Preliminary kinetic studies show that the rate of ethane dehydrogenation is higher on Cr²⁺ than on Cr³⁺ sites. Evidence supporting the presence of Cr²⁺ ions on the surface has also been provided.