Competition between NO reduction and NO decomposition over reduced V–W–O catalysts

Abstract

The SCR of NO and NO decomposition were investigated over a V–W–O/Ti(Sn)O 2 catalyst on a Cr–Al steel monolith. The conversions of NO and NH 3 over the reduced and oxidised catalysts were determined. The higher conversion of NO than of NH 3 was observed in SCR over the reduced catalyst and very close conversions of both substrates were found over the oxidised one. The increase of the pre-reduction temperature was found to cause an increase in catalyst activity and its stability in direct NO decomposition. The surface tungsten cations substituted for vanadium ones in vanadia-like active species are considered to be responsible for the direct NO decomposition. The results of DFT calculations for the 10-pyramidal clusters: V 10O 31H 12 (V–V) and V 9WO 31H 12 (V–W) modelling (0 0 1) surfaces of vanadia and WO 3–V 2O 5 solid solution (s.s.) active species, respectively, show that preferable conditions for NO adsorption exist on W sites of s.s. species and that reduction causes an increase in their ability for electron back donation to the adsorbed molecule. Electron back donation is believed to be responsible for the electron structure reorganisation in the adsorbed NO molecule resulting in its decomposition. The high selectivity of NO decomposition to dinitrogen was considered to be connected with the formation of the tungsten nitrosyl complexes solely via the W–N bond.