Characterization of Surface Chromia Species on CrOx/TiO2 Catalysts

Abstract

Titania supported chromia catalysts have been employed for selective catalytic reduction (SCR) process because of their higher activity and selectivity. The catalytic activity of the titania supported chromia system is owing to the stabilization of the anchored chromia species having multiple chemical and molecular states on the surface. In the present work an attempt has been made to prepare titania supported chromia catalysts, from TiCl₄ and CrO₃ as precursors for the support and active phase respectively. Characterization of the catalysts have been made using FTIR spectroscopy and thermo analytical techniques such as thermogravimetric analysis (TGA), evolved gas analysis (EGA) and temperature programmed reduction (TPR). The EGA, TGA and FTIR results indicate that the surface hydroxyl groups of TiO₂ (gel) has an influence on the chemical state of the chromium. Due to the surface anchoring, Cr⁺⁵ species have been detected on the surface of the fresh catalyst which decomposes to lower valence state on calcination. EGA results indicate that Cr⁺³ species having higher degree of coordinatively unsaturated centers is stabilized by gel titania as support. EG analysis and FTIR studies illustrate the coverage of the surface with similar type of sites at 10 wt.% chromia loading. TPR studies demonstrate the presence different kinds of surface chromia species with respect to chromia content.