The effect of Zn:Ti ratios on PdZn/ZnO−TiO2 catalysts for CO2 hydrogenation to methanol

Porous ZnO−TiO₂ synthesized using different Zn and Ti ratios (Zn:Ti = 0.5, 1, 2) is investigated as PdZn alloy support to optimize methanol production from CO₂ hydrogenation. XRD, Raman, and XPS analyses reveal that varying Zn ratios influence crystal structure, oxygen vacancies, surface area and ZnTiO₃ phases. The partial transformation into ZnTiO₃ occurs on the PdZn perimeter, forming strong interfacial interaction with the PdZn alloy. Higher Zn content promotes hexagonal ZnTiO₃, while lower ratios favor cubic ZnTiO₃, which leads to higher oxygen vacancy formation. High methanol selectivity was obtained below 250 °C with optimum productivity at ∼1326.8 mmolkg_cat^-1h^-1. CO is the main product at temperatures above 250 °C, while methane and C₂₊hydrocarbons from the C − C coupling reaction occur at 450 °C. In-situ DRIFTS analysis provides insight into the reaction mechanism that requires stabilization of formate *HCOO and formyl species, *HCO, for hydrogenation to methanol.