Gallium: A Universal\nPromoter Switching CO<sub>2</sub> Methanation Catalysts to Produce\nMethanol

Hydrogenation of CO<sub>2</sub> to methanol is foreseen\nas a key\nstep to close the carbon cycle. In this study, we show that introducing\nGa into silica-supported nanoparticles based on group 8–9 transition\nnoble metals (M = Ru, Os, Rh, and Ir – <i>M</i>Ga@SiO<sub>2</sub>) switches their reactivity from producing mostly methane\n(sel. > 97%) to producing methanol (>50% CH<sub>3</sub>OH/DME\nsel.)\nalongside CO as the only byproduct. These silica-supported catalysts,\nprepared <i>via</i> a surface organometallic chemistry (SOMC)\napproach, consist of small, alloyed, and narrowly distributed <i>M</i>Ga nanoparticles, as evidenced by X-ray absorption spectroscopy\n(XAS) and CO adsorption studies. Notably, detailed <i>in situ</i> XAS and diffuse reflectance Fourier transform infrared spectroscopy\n(DRIFTS) studies complemented with density functional theory (DFT)\ncalculations indicate that Ga generates stable bulk <i>M</i>Ga alloys. The bulk <i>M</i>Ga alloys persist during CO<sub>2</sub> hydrogenation according to XAS, resulting in suppressed methanation.\nMeanwhile, a small fraction of surface GaO<sub><i>x</i></sub> and thereby <i>M</i>Ga–GaO<sub><i>x</i></sub> interfaces are formed, as evidenced by IR spectroscopy, likely\nresponsible for stabilizing methoxy intermediates and favoring methanol\nformation.