High-temperature selective catalytic reduction of NO with NH₃: Optimization of ZrO₂ and WO₃ complex oxides

The catalyst for selective catalytic reduction of NO_x at high temperatures is significantly demanded by current gas-fired exhaust purification. In this work, the complex oxides composed of two different structures of ZrO₂-WO₃ and WO₃/ZrO₂ with zirconium as the main component were prepared for NH₃-SCR of NO at high temperatures by blending method and equal volume impregnation method, respectively. Combined with XRD, NH₃-TPD, FE-SEM, BET and in situ DRIFTS characterization, the effects of component optimization of two kinds of ZrO₂ and WO₃ complex oxides on the performance for NH₃-SCR of NO were mainly studied. The optimal compatibility of ZrO₂ and WO₃ complex oxides was determined, and the corresponding N₂ selectivity and anti-interference ability of water vapor and SO₂ were further investigated. Results showed that the performance of ZrO₂-WO₃ prepared by blending method for NH₃-SCR of NO was significantly better than that of WO₃/ZrO₂ prepared by impregnation method. The ZrO₂-WO₃ containing 20% WO₃ has the best performance in NH₃-SCR of NO with NO conversion higher than 90% and N₂ selectivity higher than 90% at 450–650 °C, and the performance was not affected by SO₂, slightly affected by competitive adsorption of water vapor at 450 °C and not disturbed by water vapor above 500 °C. Further investigation showed that the NH₃-SCR of NO over the ZrO₂-WO₃ reaction followed both L-H and E-R mechanisms. Characterization analysis revealed that ZrO₂-WO₃ has finer microscopic particles, larger specific surface area, higher acid amount and stronger acid strength than WO₃/ZrO₂.