Raman, FTIR and theoretical evidence for dynamic structural rearrangementsof vanadia/titania DeNOx catalysts

Insight into the selective catalytic reduction (SCR) of NO by NH3 over vana dia/titania catalysts is obtained from a combination of Raman and FTIR spec troscopic investigations and density functional theory (DFT) calculations. Studies of the V-OH and V=O functional groups under different conditions co upled with calculations of the stability and mobility of H atoms provide ev idence that dynamic structural rearrangements may occur during the SCR reac tion. Hydrogen atoms are bonded more strongly to oxygen atoms that are coor dinated to a single vanadium atom (V=O species), compared to bonding at oxy gen atoms that are coordinated to multiple vanadium atoms (e.g., V-O-V spec ies); and, activation energy barriers for hydrogen transfer from a V=O spec ies to another V=O species and to a V-O-V species are estimated from DFT ca lculations to be 60 and 130 kJ/mol, respectively. This dynamic nature of hy drogen transfer between oxygen atoms having different coordination environm ents also appears to explain some of the spectroscopic changes observed for vanadia/titania catalysts having different vanadia loadings.