CO2 hydrogenation on Cu-catalysts generated from ZnII single-sites: Enhanced CH3OH selectivity compared to Cu/ZnO/Al2O3

The hydrogenation of CO2 to CH3OH is mostly performed by a catalyst consisting mainly of copper and zinc (Cu/ZnO/Al2O3). Here, Cu-Zn based catalysts are generated using surface organometallic chemistry (SOMC) starting from a material consisting of isolated ZnII surface sites dispersed on SiO2 – ZnII@SiO2. Grafting of [Cu(OtBu)]4 on the surface silanols available on ZnII@SiO2 followed by reduction at 500 °C under H2 generates CuZnx alloy nanoparticles with remaining ZnII sites according to X-ray absorption spectroscopy (XAS). This Cu-Zn/SiO2 material displays high catalytic activity and methanol selectivity, in particular at higher conversion compared to benchmark Cu/ZnO/Al2O3 and most other catalysts. In situ XAS shows that CuZnx alloy is partially converted into Cu(0) and Zn(II) under reaction conditions, while ex situ solid state nuclear magnetic resonance and infrared spectroscopic studies only indicate the presence of methoxy species and no formate intermediates are detected, in contrast to most Cu-based catalysts. The absence of formate species is consistent with the higher methanol selectivity as recently found for the related Cu-Ga/SiO2.