Photothermal CO Hydrogenation over Ni/g‑CN Catalysts: Effect of Synthesis Methods on Structure, Activity and Mechanism.

The intensification of global climate change by CO emissions has led to increased research focus on reducing emissions and utilizing resources. Photothermal catalysis, combining photocatalytic and thermal catalytic advantages, holds promise for efficient CO conversion. g-CN, with its superior band structure and visible light responsiveness, is commonly employed in catalytic material development. Nickel, a cost-effective transition metal, exhibits strong CO adsorption and H activation capabilities, making it highly active in photothermal catalytic CO reduction. However, the structural properties of g-CN are sensitive to metal loading, with different preparation methods significantly impacting Ni particle dispersion, the metal-support interface structure, and active site exposure, thereby influencing the overall catalytic performance of g-CN. Based on this, Ni/g-CN catalysts were synthesized using co-deposition, solid-state impregnation, and the Co-pyrolysis method, where g-CN served as the carrier and Ni as the active core component. The catalysts underwent comprehensive physical and chemical characterization through SEM-EDS, TEM, XRD, FT-IR, BET, CO-TPD, H-TPR, XPS, UV-vis DRS, and photoelectrochemical analyses. The catalytic activity was assessed in the photothermal catalytic CO hydrogenation reaction, and the reaction mechanism was elucidated through in situ DRIFTS analysis. The results demonstrate that the preparation method significantly impacts the phase structure and surface properties of the catalysts, leading to performance variations. Notably, the Ni/g-CN-CD catalyst synthesized via the co-deposition method exhibits a higher specific surface area, a richer pore structure, a weaker metal-support interaction, a broader visible-light absorption range, and enhanced CO adsorption and reduction capabilities. Photoelectrochemical tests confirmed its more efficient photogenerated carrier separation and electron transport abilities. Under photothermal coupling conditions at 300 °C, the catalyst achieved a CO yield of 15937.2 μmol·g·h and a CO selectivity of 84%. Mechanistic investigations reveal that CO is hydrogenated on the catalyst surface, forming the COOH* intermediate, which then decomposes into CO and HO, with a portion of the CO further hydrogenated to CH. This study provides valuable insights for optimizing the synthesis of g-CN-based supported metal catalysts and their application in photothermal catalytic CO reduction.