Gallium: A Universal Promoter Switching CO ₂ Methanation Catalysts to Produce Methanol

Hydrogenation of CO₂ to methanol is foreseen as a key step to close the carbon cycle. In this study, we show that introducing Ga into silica-supported nanoparticles based on group 8-9 transition noble metals (M = Ru, Os, Rh, and Ir - <i>M</i>Ga@SiO₂) switches their reactivity from producing mostly methane (sel. > 97%) to producing methanol (>50% CH₃OH/DME sel.) alongside CO as the only byproduct. These silica-supported catalysts, prepared <i>via</i> a surface organometallic chemistry (SOMC) approach, consist of small, alloyed, and narrowly distributed <i>M</i>Ga nanoparticles, as evidenced by X-ray absorption spectroscopy (XAS) and CO adsorption studies. Notably, detailed <i>in situ</i> XAS and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) studies complemented with density functional theory (DFT) calculations indicate that Ga generates stable bulk <i>M</i>Ga alloys. The bulk <i>M</i>Ga alloys persist during CO₂ hydrogenation according to XAS, resulting in suppressed methanation. Meanwhile, a small fraction of surface GaO _<i>x</i> and thereby <i>M</i>Ga-GaO _<i>x</i> interfaces are formed, as evidenced by IR spectroscopy, likely responsible for stabilizing methoxy intermediates and favoring methanol formation.