Combining Atomic Layer Deposition with Surface Organometallic Chemistry to Enhance Atomic-Scale Interactions and Improve the Activity and Selectivity of Cu–Zn/SiO<sub>2</sub> Catalysts for the Hydrogenation of CO<sub>2</sub> to Methanol
Hui Zhou, Scott R. Docherty, Nat Phongprueksathat, Zixuan Chen, Andrey V. Bukhtiyarov, Igor P. Prosvirin, Оlga V. Safonova, Atsushi Urakawa, Christophe Copéret, Christoph R. Müller, Alexey Fedorov
Abstract
High Resolution Image Download MS PowerPoint Slide 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.