Promotional Effect of Zirconium Doping on the NH3-SCR Activity of CeO2 and CeO2-TA Modified by Thiourea: A Comparative Study

Zirconium (Zr) was doped to optimize the NH3-SCR activity of both CeO2 and thiourea modified CeO2-TA catalysts for comparison. Different from the promotional influence of thiourea modification on the agglomeration of CeO2, the transformation from nanoparticles to nanocubes and the formation of highly crystallized CeOSO4, Zr doping lowers the agglomeration of nanoparticles, loosens the surface morphology of catalyst and promotes the formation of Ce-Zr solid solution. Furthermore, Zr doping exhibits a synergistic promotional effect of thiourea modification on the dispersion of Ce3+ and S6+ species on the surface of CeO2, and increases the concentrations of the surface total oxygen and chemisorbed oxygen of CeO2-TA. Interestingly, Zr doping instead decreases the promotional effect of thiourea modification on the high-temperature or medium/low-temperature reducibility of catalyst, but increases both Bronsted and Lewis acid sites of CeO2-TA by inducing the highly dispersive sulfate species rather than the CeOSO4 crystal, which might be crucial to the NH3-SCR activity of Ce-based catalyst.