Promotional Effect of Molybdenum Additives on Catalytic Performance of CeO₂/Al₂O₃ for Selective Catalytic Reduction of NO_x

Abstract: A series of CeO₂/Al₂O₃ and CeMo_xO_y/Al₂O₃ catalysts were prepared by an extrusion method for selective catalytic reduction of NO_x, and were characterized by techniques of XRD, XPS, N₂-BET, H₂-TPR and NH₃-TPD. Promotional effects of molybdenum additives on catalytic performances and tolerances toward SO₂ and H₂O poisoning of the catalysts were comparatively studied. Results showed that the CeO₂/Al₂O₃ catalyst with the Ce/Al molar ratio of 1:5 exhibited the best catalytic performance; molybdenum additives greatly improved catalytic performance of the CeMo_xO_y/Al₂O₃ catalysts, and the catalyst with the Al/Ce/Mo molar ratio of 5:1:0.15 calcinated at 550 °C exhibited the highest catalytic activity above 95 % in active temperature window of 250–430 °C under the gas hourly space velocity (GHSV) of 7200 h⁻¹. Moreover, molybdenum additives broadened the range of the active temperature, and significantly enhanced the anti-sulfur poisoning ability. Analysis showed that the promotional effects of molybdenum additives were attributed to the improvement of specific surface area, increment of surface acidity and the enhancement of the redox properties. Graphical Abstract: The molybdenum additives significantly increase the catalytic performance of CeO₂/Al₂O₃ for selective catalytic reduction of NO_x and greatly broaden the range of the active temperature. The reasons mainly due to molybdenum additives improve the specific surface area, increase the proportion of Ce³⁺/(Ce⁴⁺+Ce³⁺) and O_α/(O_α + O_β) on the surface, and enhance the amount of the Lewis acid sites.[Figure not available: see fulltext.]