Ternary CuCrCeOx Solid Solution Enhances N-2-Selectivity in the NO Reduction with CO in the Presence of Water and Oxygen

Co-doping of ceria with Cu and Cr forming a ternary CuCrCeOx solid solution enhances N-2-selectivity as well as NO and CO conversions compared to the corresponding singly doped ceria, CuCeOx and CrCeOx, and pristine ceria, in the absence as well as presence of water and oxygen. The comparative study of these solid-solution catalysts indicates that the doping of ceria results in the coupling of different transition metal redox cycles, which has a strong effect on the surface population of oxygen vacancies. The temperature required to reach 95 % N-2-selectivity is shown to be nearly linearly correlated to the concentration of oxygen vacancy defects. The oxygen defect population is highest for the ternary CuCrCeOx solid solution, which exhibits the best catalytic performance, reaching 100 % N-2-selectivity at around 100 degrees C. Three redox cycles (Cr-VI/Cr-III, Cu-II/Cu-I, and Ce-IV/Ce-III) have been identified in this catalyst leading to a synergistic effect. The ternary CuCrCeOx catalyst exhibits good water tolerance and long-term stability while the SO2 tolerance is limited due to selective blocking of the active surface oxygen defects forming SO32- species, resulting in catalyst deactivation.