Probing the Reaction Mechanism in CO₂ Hydrogenation on Bimetallic Ni/Cu(100) with Near-Ambient Pressure X-Ray Photoelectron Spectroscopy

Abstract

Bimetallic Ni–Cu catalysts feature high activity in CO2 hydrogenation. However, the primary surface intermediates during reaction are still elusive, making the understanding of the reaction mechanism inadequate. Herein, taking advantage of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), we focused on the mechanistic exploration of CO2 hydrogenation on the Ni/Cu(100) model catalyst under millibar pressures. We show that CO2 dissociates into CO and atomic oxygen on the Ni/Cu(100) surface and gives rise to the formation of chemisorbed O and nickel oxide (NiO). The CO3* species is formed through the reaction of CO2 with surface oxygen during CO2 activation. With the presence of H2, the conversion of adsorbed CO3* into the formate intermediate, HCOO*, is unambiguously demonstrated by the C 1s and O 1s core-level spectra as well as ultraviolet photoelectron spectroscopy. Based on these observations, we conclude that the CO2 hydrogenation route via CO2 dissociation, the formation of CO3*, the conversion of CO3* to formate, and the ensuing hydrogenation of formate to methanol on the Ni–Cu catalyst are feasible.