Hydrophobic CuZn Catalyst for CO 2 Hydrogenation to Methanol

The byproduct water produced in the CO₂ hydrogenation to methanol process inevitably oxidizes the active Cu⁰ of Cu-based catalysts, resulting in catalyst deactivation. Here, the CuZn catalyst is prepared by the coprecipitation method and modified with Zr and chitosan to prepare CuZn@Zr and CuZn@ZrC catalysts. All of the catalysts are investigated for the hydrogenation of CO₂ to methanol. For the modified CuZn@ZrC catalyst with the carbon layer, the water contact angle remains stable at 122° even after 10 s, while that of the CuZn catalyst decreases rapidly from 124° to 39° within 2 s. The amount of desorbed CO₂ for CuZn@ZrC (320.5 μmol/g) is larger than that for CuZn (192.3 μmol/g). After a 280 h reaction at 240 °C, 3.0 MPa, and 3000 mL·h^-1·g^-1, the deactivation rate of methanol space-time yield for CuZn@ZrC is only 0.22%/h, whereas for CuZn, it is 0.33%/h. The active Cu⁰ in the spent CuZn catalyst is oxidized to Cu²⁺, which results in deactivation. The Cu⁰ in the spent CuZn@ZrC catalyst remains the dominant copper species due to the presence of a hydrophobic carbon layer that inhibits contact with water. The findings provide a framework for the design and optimization of the required catalyst with the aim of enhancing the catalytic stability in reactions involving water.