CO2 Methanation over Ni Catalysts Supported on Pr-Doped CeO2 Nanostructures Synthesized via Hydrothermal and Co-Precipitation Methods

The synthesis method of the Pr-doped CeO2 catalyst support in Ni/Pr-CeO2 CO2 methanation catalysts is varied by changing the type/basicity of the precipitating solution and the hydrothermal treatment temperature. The use of highly basic NaOH as the precipitating agent and elevated hydrothermal treatment temperature (100 or 180 °C) leads to the formation of structured Pr-doped CeO2 nanorods and nanocubes, respectively, whereas the use of a mildly basic NH3-based buffer in the absence of hydrothermal treatment (i.e., co-precipitation) leads to an unstructured mesoporous morphology with medium-sized supported Ni nanoparticles. The latter catalyst (Ni/CP_NH3) displays a high surface area, high population of moderately strong basic sites, high oxygen vacancy population, and favorable Ni dispersion. These properties lead to a higher catalytic activity for CO2 methanation (75% CO2 conversion and 99% CH4 selectivity at 350 °C) compared to the catalysts with structured nanorod and nanocube support morphologies, which are found to contain a significant amount of leftover Na from the synthesis procedure that can act as a catalyst inhibitor. In addition, the best-performing Ni/CP_NH3 catalyst is shown to be highly stable, with minimal deactivation during time-on-stream operation.