CO2 Methanation over Ni Catalysts Supported on Prdoped CeO2 Nanostructures Synthesized via Hydrothermal and Coprecipitation 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 oC) 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, and favorable Ni dispersion. These properties lead to a higher catalytic activity for CO2 methanation (75% CO2 conversion and 99% CH4 selectivity at 350 oC) 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.