Characterization of chromia-promoted γ-iron oxide catalysts and their CO conversion efficiency

Abstract

A systematic study has been conducted on the evolution of phases in chromia-promoted γ-Fe 2O 3 catalysts prepared under a wide range of conditions using different instrumental techniques, viz., DTA, XRD, TEM, IR, and Mössbauer spectroscopy. The structural parameters have been correlated with the reaction properties of the catalysts for the water gas shift reaction. It has been revealed that γ-Fe 2O 3 prepared by precipitation techniques has an imperfect spinel structure. In the wet mixing method of preparation of the catalyst, the interaction between γ-Fe 2O 3 and Cr 2O 3 is found to be insignificant, while for the coprecipitated method, the interaction takes place by the incorporation of Cr 3+ ions into the octahedral vacant sites of the γ-Fe 2O 3 lattice where chromia concentration remains below 15%, above which the crystallization of the mixed phase is hindered and the activity of the catalyst tends to decrease. The reverse coprecipitation technique with a chromia concentration of nearly 10% is found to be most effective for imparting higher CO conversion activity.