M (M = Mn, Co, Cu)-CeO2 catalysts to enhance their CO catalytic oxidation at a low temperature: Synergistic effects of the interaction between Ce3+-Mx+-Ce4+ and the oxygen vacancy defects

Abstract

CeO2-based catalyst modified by transition metals M (M = Mn, Co, and Cu) with a facle solution combustion method. A variety of characterizations and testing methods was used to analyze the effects of different doping elements and molar ratios on the crystal structure, surface morphology, valence state of the surface elements of the material, the specific surface area of the catalyst, and the reduction temperature. The best performances of the obtained Mn-CeO2, Co-CeO2, Cu-CeO2 are with the molar amount of 20%, 40% and 35%, respectively. Among them, the molar amount of 20% Mn-CeO2 catalysts show an excellent catalytic performance. The T50% of CO is as low as 70 °C (70 < T50% <151 °C), and the CO conversion efficiency of the catalyst was still above 90% after 20 h of continuous catalysis, when the relative humidity reaches 70%, the CO conversion remains at a high level of more than 80%. There are as high as 58.56% active oxygen content on its surface. The results of the test characterization show that the high- valence and low-valence ions on the catalyst surface can form a synergistic effect of Ce3+-Mx+-Ce4+ (M = Mn, Co, Cu), the synergistic effect makes the surface of the catalyst sample appear redox equilibrium reaction, and increase the number of active oxygen on the surface of the material, thereby enhancing the catalytic oxidation activity of the catalyst and improving the conversion efficiency of M(M = Mn, Co, and Cu)-CeO2 catalysts for low-temperature CO catalytic oxidation.