Identifying the presence of [V = O]2+ during SCR using in-situ Raman and UV Vis spectroscopy

Combining UV Vis and Raman spectrosocopy allows for V=O, oxo vanadium(IV) surface species to be identified during operando SCR on V2O5/TiO2 catalysts. V4+ is formed by a one electron reduction pathway by NO and NH3 and it exhibits a V-O stretch which is red shifted slightly compared to its V5+ counterpart. This is due to an extra proton charge balancing the reduced entity in form of an -OH group. This red shift is similar in nature to the effect of hydration, which is a function of water partial pressure in the gas stream and the temperature. It is shown that the red shift cannot solely be due to changes in the water contents, and that it is related to a reduction of vanadium. Furthermore, exposing the oxidized catalyst to 1.5% H2O, which is more than an order of magnitude higher than the residual water level present after the NO and NH3 reduction, induces less red shift as observed after reduction of the catalyst in the apparent dry conditions. It is further observed with UV Vis spectroscopy that NO and NH3 reduction forms a V(IV) band at 15,000 cm(-1).