Understanding the Role of Copper Oxidation State on a TiO₂/ZSM-5 Catalyst for Photocatalytic CO₂ Reduction to Methanol

This study explores the enhancement of photocatalytic CO₂ reduction to methanol using Cu-doped TiO₂/ZSM-5 catalysts. The catalysts are synthesized by wet impregnation, and the effects of calcination temperature and Cu doping are investigated. Comprehensive characterization techniques coupled with density functional theory (DFT) calculations reveal that the Cu^δ+/TiO₂/ZSM-5 (CTZ-1) catalyst exhibits the highest photocatalytic activity, yielding methanol at 0.219 mmol g_catalyst⁻¹ h⁻¹, significantly outperforming other variants. The superior performance is attributed to the increased basicity, specific surface area, unique core–shell structure morphology, and the presence of Ti³⁺ and Cu^δ+ species, which facilitate efficient electron–hole separation. The catalysts also demonstrate stable performance over multiple cycles. DFT calculations indicate that the CO₂ reduction to methanol is energetically favored at the Cu^δ+/TiO₂ interface. This work highlights the potential of Cu^δ+/TiO₂/ZSM-5 catalysts in efficient and stable photocatalytic CO₂ conversion, paving the way for further optimization of Cu^δ+ loading and doping strategies to enhance photocatalytic performance.