Effect of Surface [Cu₄O] Moieties on the Activity of Cu-Based Catalysts

Cu-based catalysts have received extensive attention in the field of catalysis due to their natural reserves, low cost, and superior catalytic performance. However, the catalytic mechanism has been debated for decades owing to the existence of various oxidation states of Cu and their dynamical evolution during the reaction process. Herein, based on first-principles theoretical calculations, a highly active [Cu₄O] moiety was identified on the partially reduced Cu₂O(111) surface. In contrast to a previous mechanism in which Cu⁰, Cu⁺, or their combination was proposed, Cu atoms in the [Cu₄O] moiety are in a fractional oxidation state (+0.5) and have bonding characteristics analogous to both metallic Cu and Cu₂O. The [Cu₄O] moiety has both electronic and geometric advantages in surface catalysis, showing high activity in methanol dehydrogenation. Experimental work further provided evidence for the existence of such mixed-valence Cu species and confirmed its high activity in methanol dehydrogenation. This work unravels the active sites in the partially reduced Cu species and provides insights into the rational design of more active Cu-based catalysts.