Low-Temperature Hydrogenation of CO₂ to Methanol in Water on ZnO-Supported CuAu Nanoalloys

Optimizing processes and materials for the valorization of CO₂ to hydrogen carriers or platform chemicals is a key step for mitigating global warming and for the sustainable use of renewables. We report here on the hydrogenation of CO₂ in water on ZnO-supported CuAu nanoalloys, based on ≤7 mol % Au. Cu_xAu_y/ZnO catalysts were characterized using ¹⁹⁷Au Mössbauer, in situ X-ray absorption (Au L_III- and Cu K-edges), and ambient pressure X-ray photoelectron (APXP) spectroscopic methods together with X-ray diffraction and high-resolution electron microscopy. At 200 °C, the conversion of CO₂ showed a significant increase by 34 times (from 0.1 to 3.4 %) upon increasing Cu₉₃Au₇ loading from 1 to 10 wt %, while maintaining methanol selectivity at 100 %. Limited CO selectivity (4–6 %) was observed upon increasing temperature up to 240 °C but associated with a ≈3-fold increase in CO₂ conversion. Based on APXPS during CO₂ hydrogenation in an H₂O-rich mixture, Cu segregates preferentially to the surface in a mainly metallic state, while slightly charged Au submerges deeper into the subsurface region. These results and detailed structural analyses are topics of the present contribution.