Heterogeneous metal/metal-oxide catalysts for CO2 reduction to methanol

The extensive use of carbon-rich sources such as coal, oil, and natural gas combustion has led to adverse environmental effects caused by the formation of CO₂, the thermodynamically favorable carbon sink. The increased concentrations of CO₂ in the atmosphere throughout the years have resulted in global warming effects, including ocean acidification, rising sea levels, and extreme climatological events. Even when long-term CO₂ storage through sequestration is possible, it is more desirable to develop technologies that capture, utilize, and recycle the carbon source to produce platform chemicals and fuels (i.e., alcohols and hydrocarbons).

The industrial production of methanol from syngas mixtures (CO₂/CO/H₂) has been practiced for decades over Cu/ZnO/Al₂O₃ at elevated pressures (5-10 MPa) and temperatures (493-573 K). However, certain limitations for Cu/ZnO/Al₂O₃ catalysts exist, including low productivity in the absence of CO, susceptibility to the poisoning of sites by water, and limited catalyst stability caused by sintering. Here, we report on a catalyst comprised of Cu/Ga₂O₃/ZrO₂ that can operate at moderate reaction conditions (533 K and 3 MPa) and yields exceptional methanol productivities and time-on-stream stability. The structural, surface, and electronic properties of Cu/Ga₂O₃/ZrO₂ were studied by temperature programmed reduction (H₂-TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results from these studies provide insight into the reaction mechanism and role of the metal-metal oxide interface in identifying catalytic compositions, resulting in increased methanol yields compared to Cu/Ga₂O₃ and Cu/ZrO₂.