Active Oxygen Species Promoted Catalytic Oxidation of 5‑Hydroxymethyl-2-furfural on Facet-Specific Pt Nanocrystals

The aerobic oxidation of alcohols and aldehydes over noble metal catalysts is a critical reaction for the catalytic conversion of carbohydrates into value-added chemicals from biomass. However, to fully understand the reaction mechanism, in particular, the role of O2 and the generated active oxygen species in these reactions is still a challenging target. In the present work, the sub-10 nm Pt nanocrystals with cubic (Pt-NCs), octahedral (Pt-NOs), and spherical (Pt-NSs) morphologies were synthesized and used as catalysts in aerobic oxidation of 5-hydroxymethyl-2-furfural (HMF). Through experimental and computational investigations, the facet-dependent O2 conversion pathway and catalytic oxidation performance were discussed. The molecular O2 tends to be dissociated to generate •OH on a Pt(100) surface but prefers to be reduced to •O2 – on a Pt(111) surface. Moreover, Pt-NCs enclosed by the {100} facets exhibited significantly enhanced catalytic activity compared to Pt-NOs enclosed by the {111} facets and Pt-NSs, in particular, for the alcohol oxidation step. On the basis of the experimental data and density functional theory (DFT) calculations, an active oxygen species promoted dehydrogenation mechanism for aerobic oxidation of HMF was proposed. The dehydrogenation of the alcohol group is more favorable on the Pt(100) surface with assistance of •OH, which is the dominant active oxygen species on the Pt(100) surface. We anticipate that this work would provide new insight into the role of active oxygen species in aerobic oxidation of alcohols and aldehydes over noble metal catalysts.