The effect of zirconia as a promoter on Cu/MOF-5 catalysts for CO2 hydrogenation to methanol

Abstract

The rise in carbon dioxide concentration is a primary anthropogenic source of severe climate change and ecological issues. Catalytic hydrogenation of CO₂ into value-added chemicals and fuels including methanol is one of the attractive environmentally friendly ways to valorize carbon-containing feedstock and reduce global CO₂ emissions. However, enhancing catalytic activity to achieve high methanol yield and selectivity while maintaining stability remains a major challenge. This study investigated the promotion of Cu/MOF-5 catalysts with varying loadings of ZrO₂ to determine its effects on catalytic performance in CO₂ hydrogenation. The copper loading was kept constant while the ZrO₂ content on the MOF-5 support was varied via the impregnation method. The addition of ZrO₂ was found to influence the BET surface area, suggesting the presence of amorphous ZrO₂, as its crystalline phases were not detected in x-ray diffractograms. Catalytic results demonstrated that ZrO₂ addition enhanced the catalytic activity, with increased CO₂ conversion up to 13.2 %. The results showed a correlation between catalytic performance and the reducibility of the active metal, driven by the amount of ZrO₂ present. The catalyst with the highest ZrO₂ loading exhibited the best performance, attributed to its increased surface area and enhanced reducibility. Under optimized conditions (GHSV of 1350 h⁻¹, temperature of 200 °C, and pressure of 30 bar), the catalyst achieved 100 % methanol selectivity. This study underscores the significant role of ZrO₂ as a promoter in enhancing the activity and selectivity of Cu/MOF-5 catalysts, providing critical insights into the design of efficient catalytic systems for CO₂ hydrogenation.