Realistic <i>Operando‐</i> DRIFTS Studies on Cu/ZnO Catalysts for CO ₂ Hydrogenation to Methanol – Direct Observation of Mono‐ionized Defect Sites and Implications for Reaction Intermediates

Our recent study in this journal highlighted misassignments of surface intermediates diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements published Cu/ZnO (CZ) catalyst systems for methanol synthesis. Here we investigate a and very active CZ system, part promoted by oxidative fluorination (i. e., Cu/ZnO1–x/ZnF2 system), with realistic operando-DRIFTS 3H2/CO2 gas feed (30 bar, 513 K). This DRIFTS setup is linked to an online GC analysis system the catalytic performance Cu/ZnO1–x showed similar catalysis process cell as test station. In measurements, broad absorption band maximum at about 1500 cm−1 (=I1500) evident. I1500 absent nitrogen; its intensity increases pure hydrogen particularly high during results from photoionization electron residing mono-ionized oxygen vacancy VO+ ZnO1–x catalyst. Consequently, provides information on extent strong metal-support interaction SMSI. Therefore, measurement could be novel efficient tool characterize any CZ-based online. Mechanistically, stream coupled reaction CO2 giving CO2−. radical anion intermediate that rapidly trapped VO2+ site formed. may react migration well-known formate (1603, 1371, 1314 cm−1). However, long-lived spectroscopic signature only spectator. It also visible samples same do not produce (GC). By contrast, intensities species 1759, 1691, 1457 1398 are directly connected production applied WHSV. these relevant hydrogenation higher pressure likely represent true adsorbates/intermediates.