Elucidating the Copper–Hägg Iron Carbide Synergistic Interactions for Selective CO Hydrogenation to Higher Alcohols

CO hydrogenation to higher alcohols (C<sub>2+</sub>OH) provides a promising route to convert coal, natural gas, shale gas, and biomass feedstocks into value-added chemicals and transportation fuels. However, the development of nonprecious metal catalysts with satisfactory activity and well-defined selectivity toward C<sub>2+</sub>OH remains challenging and impedes the commercialization of this process. Here, we show that the synergistic geometric and electronic interactions dictate the activity of Cu<sup>0</sup>–χ-Fe<sub>5</sub>C<sub>2</sub> binary catalysts for selective CO hydrogenation to C<sub>2+</sub>OH, outperforming silica-supported precious Rh-based catalysts, by using a combination of experimental evidence from bulk, surface-sensitive, and imaging techniques collected on real and high-performance Cu–Fe binary catalytic systems coupled with density functional theory calculations. The closer is the d-band center to the Fermi level of Cu<sup>0</sup>–χ-Fe<sub>5</sub>C<sub>2</sub>(510) surface than those of χ-Fe<sub>5</sub>C<sub>2</sub>(510) and Rh(111) surface, and the electron-rich interface of Cu<sup>0</sup>–χ-Fe<sub>5</sub>C<sub>2</sub>(510) due to the delocalized electron transfer from Cu<sup>0</sup> atoms, facilitates CO activation and CO insertion into alkyl species to C<sub>2</sub>-oxygenates at the interface of Cu<sup>0</sup>–χ-Fe<sub>5</sub>C<sub>2</sub>(510) and thus enhances C<sub>2</sub>H<sub>5</sub>OH selectivity. Starting from the CHCO intermediate, the proposed reaction pathway for CO hydrogenation to C<sub>2</sub>H<sub>5</sub>OH on Cu<sup>0</sup>–χ-Fe<sub>5</sub>C<sub>2</sub>(510) is CHCO + (H) → CH<sub>2</sub>CO + (H) → CH<sub>3</sub>CO + (H) → CH<sub>3</sub>CHO + (H) → CH<sub>3</sub>CH<sub>2</sub>O + (H) → C<sub>2</sub>H<sub>5</sub>OH. This study may guide the rational design of high-performance binary catalysts made from earth-abundant metals with synergistic interactions for tuning selectivity.