Enhanced low-temperature activity of CO2 methanation over Ni/CeO2 catalyst: Influence of preparation methods

The Ni/CeO2 catalysts are prepared by different methods. Accordingly, the Ni/CeO2-C catalyst synthesized by a simple precipitation and impregnation method was developed to obtain an excellent low-temperature activity for CO2 methanation. CO2 conversion reached 81.2%, and the achieved CH4 selectivity was as high as 100% even at a temperature as low as 250 °C under a high gas hourly space velocity of 30,000 mL/(g·h) over Ni/CeO2-C. After a 50 h stability test, the performance of Ni/CeO2-C still maintained CO2 conversion of 87.5% and CH4 selectivity of 100%. The characterization results show that the dispersion, particle size, and reducibility of Ni nanoparticles on the Ni/CeO2-C and Ni/CeO2-P catalysts are the same, which indicates that the physical structure of the prepared catalysts is similar, and the difference in performance is mainly caused by chemical properties. Compared to pure CeO2, the Ni/CeO2 catalyst exhibits a significantly increased amount of oxygen vacancies. According to the basic site test, there is a higher density of basic sites on Ni/CeO2-C than Ni/CeO2-P. Basic sites can also adsorb and activate CO2 molecules, which is conducive to further reaction. The presence of OH groups is crucial as they significantly influence the rate of CO2 methanation through CO2 adsorption, and activation, as well as their effects on H*. In situ DRIFTS were conducted to elucidate the reaction mechanism of CO2 methanation. Compared with pure CeO2, CO2 can be absorbed rapidly on the surface of Ni/CeO2-C catalyst, while CH4 species are detected at 200 °C.