Theoretical\nInsight into the Mechanism for the Cellobiose-to-Sorbitol\nHydrogenation Over Diatomic Ru<sub>2</sub>/NC Catalyst

Ru/NC shows a good catalytic performance in cellobiose-to-sorbitol\nhydrogenation. However, the molecular origins of the selective orientation\nof the reaction pathway remain unclear. Here, we rationally designed\nthe Ru<sub>2</sub>/NC catalyst, for which Ru2@N8 V4 is preferred as\nthe model. The hydrogenation mechanisms for the hydrogenation of β-cellobiose\nto sorbitol employing H<sub>2</sub> as the H-source in aqueous solution\nhave been investigated over Ru2@N8 V4 at the GGA-PBE/DNP level. For\nthe hydrogenation of β-cellobiose to sorbitol, the optimal reaction\npathway involves the ring-opening of cellobiose with H<sub>2</sub>O as a promoter and then the hydroreduction of aldehyde group, followed\nby the β-1,4-glycosidic bond hydrolysis. The selective orientation\nof the optimal reaction pathway originates from the dissociation of\nH<sub>2</sub>O on Ru-sites of Ru2@N8 V4 to form Brønsted acid\n(Ru–H<sup>+</sup>) and Brønsted base (Ru–OH<sup>–</sup>), which collaboratively promote the ring-opening.\nThe rate-determining steps are relative to the β-1,4-glycosidic\nbond cleavage, where an applicable π–π interaction\nbetween reactant molecule and Ru2@N8 V4 is of critical importance.\nKinetically, the β-1,4-glycosidic bond cleavage from cellubitol\nis more favorable than that from β-cellobiose. For the hydrogenation\nof β-cellobiose to cellubitol, the first ring-opening with H<sub>2</sub>O as promoter and then hydrogenation are kinetically superior\nto the direct hydrogenation and ring opening. This derives from its\ndissociation over Ru-sites to Ru–H and Ru–OH groups.\nPredictably, protic solvents (HOR) are readily dissociated into Ru–H\nand Ru–OR at Ru-sites, which can promote the ring-opening of\npyran-ring. The present research outcomes should contribute to the\ntheoretical understanding necessary for the development of novel supported\nnoble metal N-doped carbon catalysts for the hydrogenation of cellulose.