A screening study of the catalytic performance of ternary alloy nanoparticles containing nickel, iron and gallium supported on silica for methanol synthesis from CO2 and H2 was performed. Catalysts were prepared by incipient wetness impregnation and subsequently reduced in H2 before catalytic testing. Ni2FeGa showed the best performance of the tested catalysts in terms of methanol yield. An optimization of the preparation was done to improve activity and selectivity, reaching performance close to that of prepared commercially available Cu/ZnO/Al2O3/MgO at low reaction temperatures and pressure. Extensive in situ characterisation using environmental TEM, in situ XRD and in situ EXAFS of the formation of the Ni2FeGa catalyst explains an optimal reduction temperature of 550°C: warm enough that the three atomic species will form an alloy while cold enough to prevent the catalyst from sintering during the formation.