Enhancing CO2 methanation over Rh catalyst supported on ZrO2 cubic phase stabilized by MgO addition

Here, it reports the influence of MgO incorporation on the structural and catalytic properties of Rh catalysts supported on ZrO₂ for CO₂ methanation. The results show that MgO addition promotes the formation of the cubic phase of ZrO₂, leading to an increase in surface area, oxygen vacancies, and surface basicity, factors that collectively enhance CO₂ adsorption and activation under reaction conditions. Catalytic testing revealed that a low MgO content (1.7 wt %) yielded the highest CO₂ conversion (37.8 % at 325 °C), while higher MgO loadings resulted in decreased activity. Notably, the catalyst with the highest MgO content (5.5 wt %) exhibited remarkably low CO selectivity (1.4 %), indicating suppression of the reverse water-gas shift (RWGS) reaction in favor of the associative methanation pathway. This behavior is related to the increase in surface basicity, which significantly influences the nature of surface intermediates during the reaction, favoring methane formation via direct CO₂ hydrogenation. In situ FTIR analysis confirmed the presence of key intermediates, such as formate and Rh⁰–carbonyl species. As MgO content increased, the formation of Rh⁰–carbonyl species diminished, further promoting selectivity toward methane.