Ambient-Pressure CO₂ Hydrogenation to Methanol over Ni₅Ga₃ Catalysts Prepared via a Solvent-Free Route: The Influence of Structure and Composition

Abstract

Ni 5 Ga 3 -based catalysts hold promise for CO 2 reduction into methanol because the operating pressure is significantly lower than that required for commercial catalysts. While the synergy between Ni 5 Ga 3 and Ga 2 O 3 is crucial in methanol synthesis, the controllable formation of Ga 2 O 3 on Ni 5 Ga 3 nanoparticles and their structure-related interactions under varied preparation conditions remain underexplored. This study introduces a series of Ni 5 Ga 3 catalysts derived from the reduction of oxide precursors prepared via a combustion method with different fuels like oxalic acid, citric acid, and urea. Besides the combustion processes that were studied, various characterization techniques disclosed that the components and physicochemical properties of these catalysts can be strongly influenced by the choice of fuel, affecting the Ni 5 Ga 3 nanoparticle size along with the content of Ga 2 O 3 and, consequently, the catalytic performance toward CO 2 reduction. The catalysts prepared with oxalic acid were composed of the smallest Ni 5 Ga 3 nanoparticles and the most abundant Ga 2 O 3 species and thus exhibited the best performance compared to its counterpart. In addition, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis was performed to provide insights into reaction intermediates and mechanisms. This study highlights the critical role of Ga 2 O 3 in catalytic efficiency and underscores the influence of the synthesis parameters on the performance of Ni 5 Ga 3 catalysts in CO 2 hydrogenation to methanol.