Effective H2 conversion to substitute natural gas on Ni-based catalysts: role of promoters and synthesis method

The methanation of CO2 is crucial for Power-to-Gas technologies, enabling synthetic natural gas production from renewable sources. Catalyst formulation is key to tuning activity, selectivity, and reaction mechanisms. This study examines CeO2-ZrO2-supported catalysts with low Ni loading, evaluating Ru as a promoter. A detailed kinetic analysis clarifies the roles of Ni and Ru in CO2 hydrogenation, CO methanation, and the reverse water-gas shift (rWGS) reaction. Ni-based catalysts showed high activity for CO and rWGS reactions, with significantly higher rate constants than Ru-based systems. In contrast, Ru was most active for direct CO2 methanation but had negligible activity for CO methanation, resulting in lower CH4 selectivity when used alone. Mechanistic studies indicate that Ni promotes a stepwise pathway (CO2 → CO → CH4), while Ru facilitates direct CO2 hydrogenation. Co-impregnation of Ni and Ru enhanced both activity and selectivity, highlighting a synergistic effect. Among all formulations, the sequentially impregnated RuNi/CeZr_TSI catalyst outperformed others. Its success stems from combining Ru strong initial CO2 activation with Ni high CO methanation ability, leading to greater CO2 conversion and CH4 selectivity across a wide temperature range. These results confirm the promise of Ni-Ru/CeO2-ZrO2 catalysts for efficient renewable methane production.