Semi-Conductor Industry

Abstract

Irreversible deactivation of chromia/alumina dehydrogenation catalysts was investigated by deactivating the catalysts (4 wt% Cr) through prolonged calcination in air at temperatures up to 1200• C. Nitrogen physisorption, X-ray diffraction, diffuse reflectance spectroscopy in the UV-visible region, X-ray photoelectron spectroscopy, electron spin resonance spectroscopy, and catalytic measurements revealed that two deactivation mechanisms were responsible for the formation of catalytically inactive aluminaincorporated Cr 3+ species: (i) entrapment of Cr 3+ ions inside the alumina support during sintering of the alumina support and (ii) migration of Cr 3+ ions into the alumina support. Chromia that had been impregnated on alumina inhibited the phase transformation from γ-to α-alumina.