Thermoanalytical investigations on supported chromia catalysts

Abstract

Ceria- and titania-supported chromia catalysts were prepared by wet impregnation technique and their thermal stability as well as redox behaviour were examined by evolved gas analysis (EGA), thermogravimetric analysis (TGA) and temperature programmed reduction (TPR). EGA of previously calcined samples of ceria- and titania-supported chromia samples indicate the absence of bulk like behaviour due to interaction between chromia and support. Evolution of peak corresponding to mass of 44 at multistages suggests the heterogeneous nature of the surface. TG analysis under isothermal conditions suggests that the interaction is greater in ceria-supported catalytic systems. It is also observed from TG studies that the nature, population and strength of the hydroxyl groups are the determining factors for the effective interaction between active chromia phase and the support phase under severe operating conditions. TPR of ceria-supported chromia catalysts show the stabilisation of two kinds of species on the support; the first type (Peak B) being thermally stable chromate species which are reoxidisable, and the second type (Peak A) is thermally unstable species (bulk like aggregates) which are not reoxidisable after reduction or thermal decomposition. TPR studies collectively advocate the predominant prevalence of bulk like “aggregates” rather than anchored chromate species with the formation of polymeric species on increasing the chromia content.