Developing Alloyed Au-Cu/Ga₂O₃-Nanorod Catalysts for Efficient Photothermal Catalytic Conversion of CO₂ to MeOH

Converting carbon dioxide (CO₂) into valuable fuels and chemicals, such as methanol (MeOH), is crucial for reducing carbon emissions and achieving carbon neutrality. Photothermal catalysis has gained widespread attention for overcoming the limitations of conventional photo and thermal catalysis, such as low quantum efficiency and low MeOH yield. However, developing catalysts that can efficiently harvest light while achieving high CO₂ conversion to MeOH remains a great challenge. In this study, we first synthesized Ga₂O₃ nanorods (referred to as U-Ga₂O₃) by optimizing the preparation methods. Next, we developed supported Au/Ga₂O₃ and Au-Cu/Ga₂O₃ catalysts, with the latter featuring the formation of Au-Cu alloy nanoparticles. The design principle behind these catalysts is to enhance light absorption, facilitate the separation of photogenerated charge carriers, and improve the adsorption and activation of CO₂ and H₂. Under photothermal conditions at a set temperature of 250 °C and a light intensity of 390 mW/cm², we observed a MeOH generation rate of 75.9 μmol g^-1 h^-1 on U-Ga₂O₃. This rate increased to 191.4 μmol g^-1 h^-1 over 3 wt % Au/U-Ga₂O₃ and finally reached 373.3 μmol g^-1 h^-1 using the Au-Cu(1:1)/U-Ga₂O₃ catalyst. Various characterizations indicate that incorporating Cu into the Au lattice results in partial electron transfer from Au to Cu, significantly enhancing charge-carrier separation and promoting the formation of the formate species. These reaction intermediates are crucial for MeOH formation through the formate reaction pathway. Overall, this work demonstrates that the Au-Cu bimetallic catalyst holds great promise for the photothermal conversion of CO₂ to MeOH.