Nb-doped VOx/CeO2 catalyst for NH3-SCR of NOx at low temperatures

Abstract

The promotion effect of Nb addition to VO_x/CeO₂ catalysts for the selective catalytic reduction of NO_x by NH₃ was fully investigated. VO_x/CeO₂ and NbO_x doped VO_x/CeO₂ catalysts were characterized by N₂ physisorption, XRD, H₂-TPR and NH₃-TPD. The results showed that the addition of Nb could significantly promote the SCR activity of the VO_x/CeO₂ catalyst, especially in the low temperature range. VO_x/CeO₂ with 30 wt% NbO_x catalyst showed the best catalytic performance and better SO₂/H₂O tolerance than VO_x/CeO₂ catalyst. 30Nb-1VO_x/CeO₂ also exhibited higher NH₃-SCR activity than 3V₂O₅–WO₃/TiO₂. Lower crystallinity, stronger redox capability and more Brønsted acid sites of the Nb-VO_x/CeO₂ catalyst were all responsible for its more excellent NH₃-SCR performance. Based on kinetic experiments and in situ DRIFTS results, it was concluded that the Langmuir–Hinshelwood mechanism existed for selective catalytic reduction of NO over Nb-VO_x/CeO₂, in which adsorbed NO_x species reacted with adsorbed NH₃ to finally form N₂ and H₂O.