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

Abstract

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_x Au_y /ZnO catalysts were characterized using ¹⁹⁷ Au 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 Cu₉₃ Au₇ 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 H₂ O-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.