Reactivity Switch of Platinum with Gallium: From Reverse Water Gas Shift to Methanol Synthesis
Wei Zhou, Enzo Brack, Christian Ehinger, James Paterson, Jamie Southouse, Christophe Copéret
Abstract
The development of efficient catalysts for the hydrogenation of CO 2 to methanol using “green” H 2 is foreseen to be a key step to close the carbon cycle. In this study, we show that small and narrowly distributed alloyed PtGa nanoparticles supported on silica, prepared via a surface organometallic chemistry (SOMC) approach, display notable activity for the hydrogenation of CO 2 to methanol, reaching a 7.2 mol CH3OH h –1 mol Pt –1 methanol formation rate with a 54% intrinsic CH 3 OH selectivity. This reactivity sharply contrasts with what is expected for Pt, which favors the reverse water gas shift reaction, albeit with poor activity (2.6 mol CO2 h –1 mol Pt –1 ). In situ XAS studies indicate that ca. 50% of Ga is reduced to Ga 0 yielding alloyed PtGa nanoparticles, while the remaining 50% persist as isolated Ga III sites. The PtGa catalyst slightly dealloys under CO 2 hydrogenation conditions and displays redox dynamics with PtGa–GaO x interfaces responsible for promoting both the CO 2 hydrogenation activity and methanol selectivity. Further tailoring the catalyst interface by using a carbon support in place of silica enables to improve the methanol formation rate by a factor of ∼5.