Mechanistic Insights into Ni₅Ga₃ Thin Film Catalysts: An Ambient Pressure XPS and DFT Study

The intermetallic compound δ-Ni₅Ga₃ has emerged as a promising catalyst for CO2 hydrogenation to methanol, offering low-pressure operation, high selectivity, 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-Ni₅Ga₃ thin film model catalysts synthesized via magnetron sputtering to investigate these aspects under realistic reaction conditions. Combining in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS), μ-reactor activity testing, temperature-programmed desorption (TPD), and density functional theory (DFT) calculations, we reveal critical insights into the catalyst’s behavior. Our findings demonstrate: (1) dynamic surface evolution during activation, (2) the presence of key intermediates, such as formate, carboxyl, and methoxy species, which elucidate the methanol production pathway, and (3) catalyst deactivation at elevated temperatures. Notably, the study identifies distinct pathways for methanol synthesis and methanation, with methoxy formation correlating directly with methanol activity.