Gallium: A Universal Promoter Switching CO₂ Methanation Catalysts to Produce Methanol

Abstract

Hydrogenation of CO 2 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 − MGa@SiO 2 ) switches their reactivity from producing mostly methane (sel. > 97%) to producing methanol (>50% CH 3 OH/DME sel.) alongside CO as the only byproduct. These silicasupported catalysts, prepared via a surface organometallic chemistry (SOMC) approach, consist of small, alloyed, and narrowly distributed MGa nanoparticles, as evidenced by X-ray absorption spectroscopy (XAS) and CO adsorption studies. Notably, detailed in situ XAS and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) studies complemented with density functional theory (DFT) calculations indicate that Ga generates stable bulk MGa alloys. The bulk MGa alloys persist during CO 2 hydrogenation according to XAS, resulting in suppressed methanation. Meanwhile, a small fraction of surface GaO x and thereby MGa−GaO x interfaces are formed, as evidenced by IR spectroscopy, likely responsible for stabilizing methoxy intermediates and favoring methanol formation.