Effect of MoO3 on vanadium based catalysts for the selective catalytic reduction of NOx with NH3 at low temperature

The selective catalytic reduction (SCR) activities of the MoO₃ doped V/WTi catalysts prepared by the incipient wetness impregnation method at low temperature were investigated. The results showed that the addition of MoO₃ could enhance the NO_x conversion at low temperature and the best SCR activity was obtained when the dosage of MoO₃ reached 5 wt.%. The NH₃-TPD and DRIFTS experiments indicated that the addition of MoO₃ changed the type and number of acid sites on the surface of catalysts and reaction activities of acid sites were altered at the same time. The redox capacity and amount of active oxygen species got improved for V3Mo5/WTi catalyst, which could be confirmed by the H₂-TPR and transient response experiments. Water vapor inhibited the NO_x conversion at low temperature. Deposition of ammonium sulfate or bisulfate might be main reason for the loss of catalytic activity in the presence of SO₂ at low temperature. Choosing the suitable NH₃/NO ratio and elevation of reaction temperature both could weaken the influence of SO₂ on the SCR activity of the V3Mo5/WTi catalyst. Thermal treatment of the deactivated catalyst at 350°C could get the low temperature activity recovered. The decrease of GHSV improved the deNO_x efficiency at low temperature and we speculated that the rational technological process and operation parameters could contribute to the application of this kind of catalysts in real industrial environment.