Mechanistic insights into methanol production on Ni5Ga3 thin films: An in situ XPS and DFT study

The intermetallic compound δ -Ni 5 Ga 3 has emerged as a promising catalyst for CO 2 hydrogenation to methanol, offering high selectivity at low-pressure operation, and enhanced stability compared to conventional Cu/ZnO catalysts. However, the fundamental understanding of its active sites, reaction mechanisms, and deactivation pathways remains incomplete, hindering its further development. In this study, we utilize well-defined δ -Ni 5 Ga 3 thin film model catalysts synthesized via magnetron sputtering to investigate these aspects under realistic reaction conditions. We investigate the evolution of the catalyst with temperature employing in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS) at 300 mbar, microreactor activity measurements, temperature-programmed desorption (TPD), and density functional theory (DFT) calculations. Our experiments show the active catalyst as mostly metallic with only small amounts on oxidized gallium, which gradually reduces and gives way to an increased nickel-concentration at the surface at higher temperatures, accompanied by carbide-growth. We further observe the temperature-evolution of key intermediates, such as carboxyl, formate, and methoxy species. Based on these observations, we discuss distinct pathways for methanol synthesis and CO 2 methanation, with methoxy formation correlating directly with methanol activity, as well as the deactivation mechanism. • Thin-film catalysts can be especially pure and suited for mechanistic studies. • Temperature evolution of key intermediates observed with AP-XPS at 300 mbar. • Coverage of oxygen-containing adsorbate species decreases with increasing temperature. • Methoxy on the surface correlates with methanol production. • Carbide formation via the CO+RWGS pathway may contribute to deactivation.