The conversion of CO₂ to liquid fuels has garnered significant attention in recent years, as a strategy to mitigate anthropogenic CO₂ emissions and as an alternative feedstock to fossil fuels.^[1] In particular, the direct conversion of CO₂ to CH₃OH has been highlighted as an appealing target.^[2] For this purpose, metallic nanoparticles supported on oxide supports, modified with various promoters, have been extensively studied. For the most part, efforts have focused on copper particles promoted by zinc oxide/alumina (Cu/ZnO/Al₂O₃) or related copper/zirconia (Cu/ZrO₂) systems.^[3] However, Cu-based catalysts show low activity and relatively rapid deactivation by water.^[4] To combat this, alternative transition metals, oxide promoters and supports have been proposed and investigated.^[3] In particular, Pd-containing systems (Pd/MO_x, M = In, Ga, Zn) show superior activities with respect to Cu-based systems. ^[5,6]

Here, we report that small, narrowly distributed alloyed PdGa nanoparticles supported on Ga-doped silica (PdGa@SiO₂), prepared through a Surface Organometallic Chemistry (SOMC) approach, selectively catalyze the conversion of CO₂ to CH₃OH.  The bimetallic material PdGa@SiO₂ material is 40 times more active than the monometallic material (Pd@SiO₂), and an order of magnitude more active than benchmark Cu-based systems in the hydrogenation of CO₂ to CH₃OH. In contrast to most Cu-based systems, methanol selectivity appears to be largely independent of conversion. Through the use of rationally designed molecular precursors, amenable to an SOMC approach, we show that the presence of a PdGa alloy in the precatalyst is critical for the selectivity of CO₂-to-methanol in Pd-based systems doped with Ga. Furthermore, the presence of an alloyed phase in reaction conditions was confirmed by in situ X-ray Absorption Spectroscopy (XAS), and the partial re-oxidation of metallic gallium in reaction conditions was tracked using XAS. 

[1] E. V Kondratenko, G. Mul, J. Baltrusaitis, G. O. Larrazábal, J. Pérez-Ramírez, Energy Environ. Sci. 2013, 6, 3112–3135.
[2] A. Goeppert, M. Czaun, J.-P. Jones, G. K. Surya Prakash, G. A. Olah, Chem. Soc. Rev. 2014, 43, 7995–8048.
[3] X. Jiang, X. Nie, X. Guo, C. Song, J. G. Chen, Chem. Rev. 2020, DOI 10.1021/acs.chemrev.9b00723.
[4] M. Sahibzada, I. S. Metcalfe, D. Chadwick, J. Catal. 1998, 174, 111–118.
[5] S. E. Collins, M. A. Baltanás, A. L. Bonivardi, J. Catal. 2004, DOI 10.1016/j.jcat.2004.06.012.
[6] S. R. Docherty, E. Lam, G. Noh, O. V. Safonova, C. Coperet, Manuscript Submitted