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. CuxAuy/ZnO catalysts were characterized using 197Au Mössbauer, in-situ X-ray absorption (Au LIII- and Cu K-edges), and ambient pressure X-ray photoelectron spectroscopy (APXP), 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 mainly metallic state, while slightly charged Au submerges deeper into the subsurface region. These results and detailed structural analyses are topics of present contribution.