Role of Basic Sites on Cu/ZrO2 Catalysts Modified with Citric Acid in the Hydrogenation of CO2 to Methanol

The hydrogenation of CO₂ to methanol is one of the most industrially promising measures to solve the excessive emission of CO₂, although the development of highly active methanol catalysts is still a challenge. Herein, different modification methods of citric acid in the Cu/ZrO₂ catalyst system are compared, and the quantities and strengths of the basic sites of the catalysts could be adjusted by changing the modification method of citric acid. Using various characterization methods, it was found that introducing an appropriate amount of citric acid during the preparation of the support could form a complex with the zirconium dioxide precursor, which can significantly change the distribution of basic sites and the number of hydroxyl groups on the surface of the support. Moreover, the catalyst can generate more oxygen vacancies, enhance the interaction between the metal and the support, and significantly improve the adsorption and activation of the reaction gas. Compared with the unmodified catalyst, the space-time yield of methanol increases from 300 to 660 g_MeOH·h^–1·kg_cat^–1 under the reaction conditions of 260 °C and 3.0 MPa. This strategy and the experimental results provide a novel understanding of citric acid modification and the role of basic sites in the conversion of CO₂ to methanol.