A catalytic sites contiguity study on atomically-dispersed ZnO-Cu/SiO2 catalysts to improve methanol formation from CO2 hydrogenation

Cu-ZnO-based catalysts are commonly used in research on catalytic carbon dioxide (CO₂) hydrogenation for methanol (MeOH) synthesis. This work studied the catalytic sites contiguity, for example, the surface orientation or arrangement of the CO₂ and H₂ activating sites and their capability to facilitate the interaction between the adsorbed species, and its effects on the catalytic performance of MeOH formation. Cu/SiO₂ precursor was prepared by impregnating copper nitrate solution on a commercial SiO₂ gel. Controlling the exposure time and cycle numbers in atomic layer deposition (ALD), atomic-level dispersion of ZnO (ADZn) was formed on the uncalcined and calcined Cu/SiO₂ precursors as well as on the SiO₂ gel. Characterizations allowed for identification of Cu⁺–Cu⁰ and ADZn²⁺–Cu⁺/Cu⁰ sites contiguity on the reduced catalyst surface. Catalytic performance tests showed that the ALD ZnO-Cu/SiO₂-C catalyst facilitated the MeOH space–time yield to 33.1 g/(kg_catal ∙ h) at 240°C, three times the yield of its Cu-only counterpart. The property–performance correlation indicated that two types of ZnO–Cu sites contiguity were responsible for MeOH and CO formation from CO₂ hydrogenation with the ADZn²⁺–Cu⁺/Cu⁰ favouring more MeOH formation. The various contiguity of ADZn²⁺–Cu⁺/Cu⁰ sites also influence the MeOH formation from CO₂ hydrogenation.