Selective catalytic oxidation of ammonia to nitrogen over CuO-CeO2 mixed oxides prepared by surfactant-templated method

The selective catalytic oxidation of ammonia to nitrogen (NH3-SCO) has been studied over CuO-CeO2 mixed oxides. The active Cu component was doped into the CeO2 by surfactant-templated method. The finely dispersed CuO, Cu-O-Ce solid solution and bulk CuO species were detected in CuO-CeO2 mixed oxides. When the Cu loading was 10 wt% and the calcination temperature was 500 °C, CuO-CeO2 catalyst exhibited the highest molar ratio of the finely dispersed CuO species and the smallest CeO2 particles in size, and simultaneously possessed the highest level of activity. The finely dispersed CuO species was the main adsorbed sites of NH3 molecules, and the NH3(ad) could be further activated and transformed into NHx species by ceria under the roles of quick change of chemical state in near-surface region and the strong electron state interaction in CuO-CeO2 catalysts. The synergetic interaction between the two components played an important role in NH3 activation and oxidation. In addition, the activated intermediates (NHx) could also react with lattice oxygen provided by Cu-O-Ce solid solution to form N2, N2O and H2O, which was confirmed by XPS, EPR and NH3-TPR analysis. Moreover, gas oxygen could refill the oxygen vacancies to replenish the lattice oxygen consumed by NHx species. The Cu-O-Ce solid solution promoted the activation of gas oxygen as well as the formation and migration of lattice oxygen in NH3-SCO reaction, and the formed rapid reduction–oxidation cycle was essential for the higher activity of NH3 oxidation.