Insights into the role of CuO in the CO2 photoreduction process

The CO₂ photoreduction process to produce light hydrocarbons is known to be influenced by the presence of CuO nanoparticles, but the actual role of this material, whether as a catalyst or a reactant, has not yet been revealed. In this work, we investigate the role of CuO nanoparticles produced by a solvothermal method as a catalyst in CO₂-saturated water reaction media under UV light, considering the effects of different electrolytes (Na₂C₂O₄, KBrO₃, and NaOH) and temperatures on nanoparticle phase and activity. The electrolyte strongly influenced product selectivity (NaOH led to evolution of CH₄, Na₂C₂O₄ to CO, and KBrO₃ to O₂) and induced CuO phase change. A long-term analysis of these processes indicated that during the initial steps, CuO acted as a reactant, rather than as a catalyst, and was converted to CuCO₃.Cu(OH)₂, while the as-converted material acted as a catalyst in CO₂ photoreduction, with conversion values comparable to those reported in the literature.