Hydrogen‐Binding‐Initiated Activation of O−H Bonds on a Nitrogen‐Doped Surface for the Catalytic Oxidation of Biomass Hydroxyl Compounds

Abstract

Hydrogen binding of molecules on solid surfaces is an attractive interaction that can be used as the driving force for bond activation, material‐directed assembly, protein protection, etc. However, the lack of a quantitative characterization method for hydrogen bonds (HBs) on surfaces seriously limits its application. We measured the standard Gibbs free energy change (ΔG0) of on‐surface HBs using NMR. The HB‐accepting ability of the surface was investigated by comparing ΔG0 values employing the model biomass platform 5‐hydroxymethylfurfural on a series of Co‐N‐C‐n catalysts with adjustable electron‐rich nitrogen‐doped contents. Decreasing ΔG0 improves the HB‐accepting ability of the nitrogen‐doped surface and promotes the selectively initiated activation of O−H bonds in the oxidation of 5‐hydroxymethylfurfural. As a result, the reaction kinetics is accelerated. In addition to the excellent catalytic performance, the turnover frequency (TOF) for this oxidation is much higher than for reported non‐noble‐metal catalysts.

Catalytic Activation of Molecular Oxygen Toward Producing Hydroxyl Radicals Controllably for Highly Selective Oxidation of Hydroxyl Compounds under Mild Conditions

“…In the presented transmission electron microscopy (TEM) image (Figure a) and aberration-corrected high-angular annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) image (Figure i), no metallic cobalt or cobalt oxide nanoparticles were detected on the graphitic carbon sheet structure of Co–N–C, which was consistent with the X-ray diffraction (XRD) pattern (Figure m). The diffraction peaks at 25 and 43 degrees corresponded to the (002) and (004) planes of carbon, respectively, indicating a higher degree of graphitization . The energy dispersive X-ray spectroscopy (EDX) analysis revealed that Co, N, and O were homogeneously dispersed on the carbon matrix (Figure b–d).…”

“…The diffraction peaks at 25 and 43 degrees corresponded to the (002) and (004) planes of carbon, respectively, indicating a higher degree of graphitization. 27 The energy dispersive X-ray spectroscopy (EDX) analysis revealed that Co, N, and O were homogeneously dispersed on the carbon matrix (Figure 1b−d). As revealed by the X-ray absorption near-edge structure (XANES) analysis, the Co−N−C had almost the same first inflection point (E 0 value) as the CoO sample (Figure 1e), and the valence state of cobalt in Co−N−C was +2.…”

“…26−30 We proposed a strategy by using hydrogen binding-initiated activation of O−H bonds to realize the highly efficient oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA). 27 Although the reaction kinetics was clearly promoted, the dependence of the reaction on temperature still persisted. The activity declined seriously once the temperature is lower than 80 °C, which is consistent with the mostly adopted temperature range of 80−130 °C for non-noble metal catalysts.…”

“…Our laboratory has been conducting a series of studies on catalytic selective oxidations of biomass feedstocks to synthesize chemicals with O 2 . − We proposed a strategy by using hydrogen binding-initiated activation of O–H bonds to realize the highly efficient oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) . Although the reaction kinetics was clearly promoted, the dependence of the reaction on temperature still persisted.…”

Accelerating Selective Oxidation of Biomass-Based Hydroxyl Compounds with Hydrogen Bond Acceptors

“…It provides the guidance for promoting the initiated activation O−H bonds in biomass-based hydroxyl compounds. 24 Herein, we demonstrate hydrogen bond acceptors as reactivity and selectivity regulator for the catalytic oxidation of biomass-based hydroxyl compounds under neat conditions. In contrast to employing excessive hydrogen bond acceptors which deactivate the aerobic oxidation, we show that the addition of catalytic number of molecular hydrogen bond acceptors to the neat hydroxyl reactants results in much enhanced reactivity in the aerobic oxidation over the vanadium catalyst to selectively produce the corresponding aldehydes.…”