On the nature of Cu–carbon interaction through N-modification for enhanced ethanol synthesis from syngas and methanol

Abstract

Direct conversion of syngas into ethanol is an attractive process because of its short route and high-added value, but remains an enormous challenge due to the low selectivity caused by unclear active sites. Here, the Cu(111) supported N-modified graphene fragments C_13−mN_m/Cu(111) (m = 0–2) are demonstrated to be an efficient catalyst for fabricating ethanol from syngas and methanol. Our results suggest that the Cu–carbon interaction not only facilitates CO activation, but also significantly affects the adsorption stability of C₂ intermediates and finally changes the fundamental reaction mechanism. The impeded hydrogenation performance of C₁₃/Cu(111) due to the introduced Cu–carbon interaction is dramatically improved by N-doping. Multiple analyses reveal that the promoted electron transfer and the enhanced electron endowing ability of C_13−mN_m/Cu(111) (m = 1–2) to the co-adsorbed CH₃CH_xOH (x = 0–1) and H are deemed to be mainly responsible for the remarkable enhancement in hydrogenation ability. From the standpoint of the frontier molecular orbital, the decreased HOMO–LUMO gap and the increased overlap extent of HOMO and LUMO with the doping of N atoms also further verify the more facile hydrogenation reactions. Clearly, the Cu–carbon interaction through N-modification is of critical importance in ethanol formation. The final hydrogenation reaction during ethanol formation is deemed to be the rate-controlling step. The insights gained here could shed new light on the nature of Cu–carbon interaction in carbon material modified Cu-based catalysts for ethanol synthesis, which could be extended to design and modify other metal–carbon catalysts.