High-Pressure and Low-Temperature CO₂ Hydrogenation to DME over an Oxalate-Derived Bifunctional Catalyst: In Situ Synchrotron-FTIR Analysis

This work investigates Cu-based catalysts for hydrogenation of CO₂ to methanol and dimethyl ether (DME), emphasizing the role of oxalic acid (OxA) functionalization in enhancing copper dispersion and reducibility. A bifunctional Cu-ZnO-ZrO₂/zeolite (CBV3024E) system was synthesized via gel-oxalate coprecipitation (CZZ-CBV-OX) and compared with a conventional sodium bicarbonate-precipitated catalyst (CZZ-CBV-SB). Comprehensive characterization via N₂O titration and XRD shows that CZZ-CBV-OX contains smaller copper crystallites (∼10.8 nm) with higher dispersion (8%), while in situ synchrotron-FTIR microspectroscopy identifies formate intermediates and pronounced Brønsted acidity─factors that collectively enhance DME synthesis. Under mild conditions (200 °C, 2.5 MPa), the catalyst achieved 95% DME selectivity at 19% CO₂ conversion, with a space-time yield of 0.93 g g_cat^-1 h^-1 and negligible CO formation. Long-term tests over 120 h confirmed the stability of CZZ-CBV-OX. These findings highlight the effectiveness of oxalate-based catalyst preparation and underscore the importance of Brønsted acidity─verified by synchrotron IR analyses─in promoting selective CO₂ hydrogenation to DME.