CO2 Hydrogenation Using Size-dependent Ru Particles Supported on g-C3N4

•CO2 hydrogenation performance displayed a dependency on Ru active sites’ morphology.•Ru nanocluster on C3N4 balances the CO2 conversion activity and stability, which outperformed Ru single atom or Ru nanoparticles supported by C3N4.•In situ DRIFTS hints the over-activation of CO2 may trigger the deactivation of Ru/C3N4 catalyst Efficient catalysis of CO2 hydrogenation holds significant promise for addressing environmental concerns and advancing sustainable energy solutions. In this study, we report the synthesis of a novel series of Ru-supported on graphitic carbon nitride (g-C3N4) catalysts, with a focus on the impact of ruthenium (Ru) loading on the thermocatalytic performance. Varying Ru concentrations were introduced, including 0.2, 0.5, 1.0, 2.0, and 5.0 wt%, resulting in different Ru particle sizes on g-C3N4 support. Through a multifaceted characterization approach, it was observed that the catalyst containing 1 wt% Ru loading displayed superior performance, with a high density of active sites, indicated by an enhanced CO2 conversion rate of 36.8 % at 450 °C and a CO yield of 25 %. This catalyst also exhibited remarkable CO selectivity of 83 % at 375 °C. Conversely, lower loadings of 0.2 and 0.5 wt % Ru were found to be less effective, yielding minimal CO2 conversion. Loadings above 1 wt% Ru, while achieving high CO2 conversion, demonstrated a preference for CH4 production over CO, indicating lower selectivity for the desired product. This study elucidates the critical role of Ru nanocluster size in the catalytic activity and selectivity, with 1 wt % Ru-supported g-C3N4 emerging as a promising candidate for selective CO generation from CO2 hydrogenation, offering a pathway for the valorization of CO2 as a raw material in the chemical industry.