Combining Atomic Layer Deposition with Surface Organometallic Chemistry to Enhance Atomic-Scale Interactions and Improve the Activity and Selectivity of Cu-Zn/SiO 2 Catalysts for the Hydrogenation of CO 2 to Methanol.

The direct synthesis of methanol via the hydrogenation of CO 2 , if performed efficiently and selectively, is potentially a powerful technology for CO 2 mitigation. Here, we develop an active and selective Cu-Zn/SiO 2 catalyst for the hydrogenation of CO 2 by introducing copper and zinc onto dehydroxylated silica via surface organometallic chemistry and atomic layer deposition, respectively. At 230 °C and 25 bar, the optimized catalyst shows an intrinsic methanol formation rate of 4.3 g h -1 g Cu -1 and selectivity to methanol of 83%, with a space-time yield of 0.073 g h -1 g cat -1 at a contact time of 0.06 s g mL -1 . X-ray absorption spectroscopy at the Cu and Zn K-edges and X-ray photoelectron spectroscopy studies reveal that the CuZn alloy displays reactive metal support interactions; that is, it is stable under H 2 atmosphere and unstable under conditions of CO 2 hydrogenation, indicating that the dealloyed structure contains the sites promoting methanol synthesis. While solid-state nuclear magnetic resonance studies identify methoxy species as the main stable surface adsorbate, transient operando diffuse reflectance infrared Fourier transform spectroscopy indicates that μ-HCOO*(ZnO x ) species that form on the Cu-Zn/SiO 2 catalyst are hydrogenated to methanol faster than the μ-HCOO*(Cu) species that are found in the Zn-free Cu/SiO 2 catalyst, supporting the role of Zn in providing a higher activity in the Cu-Zn system.