Unveiling the Role of Zn/Zr Ratios in ZnO/ZrO2 Catalysts Prepared via Reverse Co-precipitation Method for Efficient CO2 to Methanol Conversion

This study evaluates the catalytic performance of ZnO/ZrO2 catalysts, which were synthesized through reverse co-precipitation with Zn/(Zn + Zr) ratios varying from 0 to 100%, for converting CO2 into methanol (CH3OH). The catalysts underwent systematic characterization using XRD, TEM-EDS mapping, N2 adsorption-desorption, XPS, and TPD-MS techniques, focusing on both H2 and CO2 interactions. Results showed that pure ZnO typically forms as aggregated needles, while pure ZrO2 manifests as clustered aggregates of significantly smaller nanoparticles. At lower Zn contents (20-30%), ZnO particles are small and evenly distributed among the ZrO2 nanoparticles, effectively inhibiting ZrO2 aggregation. Conversely, at higher Zn contents (40-80%), ZnO particles increase in size, while ZrO2 particles remain smaller and tend to accumulate predominantly on the surfaces of the larger ZnO particles. Catalysts with a predominance of ZnO contents exhibited greater H2 adsorption, whereas those with higher ZrO2 contents showed increased CO2 adsorption. The Zn60Zr40 (60 wt % Zn) catalyst was identified as optimal, achieving 11.8% CO2 conversion at 340 °C, with a peak CH3OH selectivity of 74.0% at 320 °C and a CH3OH yield of 6.1% at 340 °C, maintaining excellent stability over 100 h. Furthermore, the study found a direct correlation between catalytic activity and gas adsorption: higher H2 adsorption rates significantly improved CO2 conversion, while CH3OH selectivity was more influenced by CO2 adsorption. These findings underscore the importance of adsorptive properties in determining product distribution and offer essential insights for designing ZnO/ZrO2 catalysts optimized for efficient CH3OH production from CO2 hydrogenation.