Magnetron Sputtering of Pure δ-Ni₅Ga₃ Thin Films for CO₂ Hydrogenation

Previous studies have identified δ-Ni₅Ga₃ as a promising catalyst for the hydrogenation of CO₂ to methanol at atmospheric pressure. Given its recent discovery, the current understanding of this catalyst is very limited. Additionally, the presence of multiple thermodynamically stable crystal phases in the Ni/Ga system complicates the experiments and their interpretation. Conventional synthesis methods often result in the production of unwanted phases, potentially leading to incorrect conclusions. To address this issue, this study focuses on the synthesis of pure δ-Ni₅Ga₃ using magnetron sputtering deposition followed by low-temperature H₂ annealing. Extensive characterization confirmed the reproducible synthesis of well-defined δ-Ni₅Ga₃ thin films. These films, deposited directly into state-of-the-art μ-reactors, demonstrated methanol production at low temperatures and maintained a high stability over time. This method allowed for detailed surface and bulk characterization before and after the reaction, providing a comprehensive understanding of the deactivation mechanism. Our findings significantly contribute to the understanding of the Ni/Ga system and its behavior during catalytic activity, deactivation, and regeneration. This study also sets an example of how physical synthesis methods such as magnetron sputtering can be effectively employed to investigate complex catalytic systems, offering a viable alternative to more elaborate chemical methods.