Copper–Zinc Alloy-Free Synthesis of Methanol from Carbon Dioxide over Cu/ZnO/Faujasite

Abstract

The mechanism of carbon dioxide hydrogenation to methanol over Cu/ZnO materials has been explored for decades; however, the question of the active site still remains open to discussion. We used operando time-resolved X-ray absorption spectroscopy (XAS) and time-resolved isotope labeling experiments coupled with Fourier transform infrared (FTIR) spectroscopy and mass spectrometry (MS) analysis to elucidate the reaction mechanism and study the active sites and intermediates over a Cu/ZnO catalyst during carbon dioxide conversion into methanol. No reduction of the zinc oxide or formation of a copper–zinc alloy was observed even under highly reducing conditions (15 bar of hydrogen, 260 °C), which leads to the conclusion that a copper–zinc alloy phase is not required for high methanol yields and selectivity to be obtained. We attribute the reactive superiority of the copper–zinc-based system to the interplay between copper and zinc oxide phases. Our synthesis protocol provides a way to produce this copper–zinc oxide interface, without having to go through an alloy phase. © 2020 American Chemical Society