Effect of the synthesis variables on the performance of Cu/Al2O3 catalysts for enhanced CO2 dry reforming and hydrogenation

Abstract

The catalytic conversion of carbon dioxide (CO2) into value-added chemicals and fuels offers a sustainable approach to mitigating greenhouse gas emissions. Among the most promising strategies are dry reforming of methane (DRM) and CO2 hydrogenation to methanol, which yield syngas and methanol, respectively—key intermediates in synthetic fuel production. In this study, Cu/Al2O3 catalysts are synthesized by wet impregnation using γ-Al2O3 as the support, systematically varying synthesis parameters such as copper (Cu) loading (5–20 wt%), precursor salts (nitrate and acetate), solvents (water, methanol, ethanol), additives (citric acid), and additional treatments (hydrothermal and sonication), followed by thermal treatment at 300 °C. The catalysts are characterized by XRD, nitrogen (N2) adsorption–desorption, H2-TPR, HRTEM, and XPS to determine crystallinity, dispersion, redox behavior, and surface properties. Catalytic performance is subsequently assessed in both DRM (450–700 °C, 1 bar) and CO2 hydrogenation (200–325 °C, 30 bar). Results reveal that Cu dispersion, location, and oxidation state strongly depend on synthesis conditions and critically affect catalytic performance. The highest activities are achieved by catalysts prepared with copper nitrate precursors combined with citric acid-assisted impregnation or higher Cu loadings. These formulations demonstrate superior CuO dispersion, improved redox properties, and enhanced modification of the porous structure. This study highlights the critical influence of synthesis parameters in determining Cu/Al2O3 catalyst performance and offers valuable insights for designing multifunctional, efficient, and scalable systems for sustainable CO2 valorization.