CO2 hydrogenation to methanol is of great environmental and economic interest due to its potential to reduce carbon emissions and produce valuable chemicals in one single reaction. Compared with the unmodified traditional Cu/ZnO/Al2O3 catalyst, an indium oxide (In2O3)-based catalyst can double the methanol selectivity from 30–50 to 60–100%. It is worth noting that over catalysts involving various active metals dispersed on indium oxide (M/In2O3, M = Pd, Ni, Au, etc.), although the methanol yield is boosted, the selectivity remains similar to that of plain In2O3 despite the distinct chemical properties of the added metals. To investigate the phenomena behind this behavior, here we used RuO2/In2O3 as a test catalyst. The results of ambient pressure photoelectron spectroscopy, in situ X-ray absorption fine structure, and time-resolved X-ray diffraction indicate that the structure of the RuO2/In2O3 catalyst is highly dynamic in the presence of a reactive environment. Specifically, under CO2 hydrogenation conditions, Ru clusters facilitate the reduction of In2O3 to generate In2O3–x aggregates, which encapsulate the Ru systems in a migration driven by thermodynamics. In this way, the Ru0 sites for CH4 production are blocked while creating RuO x –In2O3–x interfacial sites with tunable metal–oxide interactions for selective methanol production. In an inverse oxide/metal configuration, indium oxide has properties not seen in its bulk phase that are useful for the binding and conversion of CO2. This work reveals the dynamic nature of In2O3-based catalysts, providing insights for a rational design of materials for the selective synthesis of methanol.

No abstract

A combination of environmental-transmission electron microscopy (E-TEM), several in-situ techniques (XRD, PDF, XAFS, AP-XPS), and transient isotopic exchange analysis was used to explore links between the structural and chemical properties of a Cu@TiOx core@shell catalyst under CO2 hydrogenation conditions. The active phase of the catalyst involved an oxide/metal configuration, but the initial core@shell motif was disrupted. Images of E-TEM showed a very dynamic morphology, where the inverse oxide/metal configuration was substantially affected by the gas environment (CO2, H2, or CO2/H2) and the temperature of the system. At room temperature, CO2 was very reactive at the metal-oxide interface, producing big changes in its morphology. When the initial system was oxidized by reaction with carbon dioxide (CO2,gas → COgas + Oads), the copper leached out and disrupted the titania shell. However, the core@shell structure was regenerated by hydrogen reduction at 150-250 oC. When oxidation and reduction occurred at the same time, under a mixture of CO2 and H2, the surface structure evolved toward a dynamic equilibrium that strongly depended on the temperature. At room temperature, the leaching of copper dominated, while, at 250 °C, the formation and development of an evolving Cu@TiOx structure prevailed. These morphological changes were linked to variations in metal-support interactions that were completely reversible with temperature or chemical environment and affected the catalytic activity of the system.