Insight into activation of CO and initial C2 oxygenate formation during synthesis of higher alcohols from syngas on the model catalyst K2O/Cu(111) surface

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Alkali-metal-modified Cu-based catalysts are important in low-temperature synthesis of methanol and higher alcohols from syngas. Spin-polarized density functional theory calculations with periodic slab models were performed for a K2O/Cu(111) model catalyst to investigate the interactions between K2O and the Cu(111) surface, and activation of CO. The results show that K2O interacts strongly with the Cu(111) surface via electron transfer between K2O and the Cu(111) surface. This changes CO activation and modulates the mechanism of formation of the initial C2 oxygenates. Although K2O significantly promotes CO direct dissociation, H-assisted dissociation of CO is still the most energetically favorable route. The optimal reaction pathway for C2 oxygenate formation is proposed based on a climbing-image nudged elastic band calculation. The reactions starts with CO hydrogenation to yield the preferred monomers, i.e., CHO, CH2O, and CH2, through the pathways CO + H → CHO + H → CH2O + H → CH2 + OH, with reaction barriers of 0.92, 0.97, and 0.58 eV. The reaction of CH2 with CH2O is the main C2 oxygenate formation route on the K2O/Cu(111) surface. These results clarify the effects of K2O on Cu-based catalysts and elucidate the mechanism of C2 oxygenate formation during alcohol synthesis from syngas.