Integrated Catalytic Sites for Highly Efficient Electrochemical Oxidation of the Aldehyde and Hydroxyl Groups in 5-Hydroxymethylfurfural

Abstract

5-Hydroxymethylfurfural oxidation reaction (HMFOR) is regarded as a promising approach to attain biomassderived high-value chemical products. As the HMFOR process is complicated, and the two-step oxidation of the aldehyde group and hydroxyl group in 5-hydroxymethylfurfural (HMF) is typically involved, it is fundamentally significant to understand the different catalytic processes for HMFOR. In this work, we identify direct and synergistic oxidation types for HMFOR on cobalt oxide catalysts. For the direct HMFOR process, Co 3 O 4 was found to have a higher activity for the aldehyde group than for the hydroxyl group due to the higher reaction barrier of hydration in the hydroxyl oxidation. By studying the hydroxyl oxidation behaviors in transition metal oxides, NiO exhibited optimal hydroxyl activity owing to the appropriate OH adsorption energy for alcohol dehydrogenation. Therefore, the optimal HMFOR performance was achieved by accurately introducing Ni into the tetrahedral catalytic sites of cobalt spinel oxides to improve the hydroxyl activity. The integrated catalytic sites enhanced the overall activity of HMFOR with 92.42% FDCA yield and 90.35% faradaic efficiency. This work provides a promising perspective for designing efficient electrocatalysts for HMFOR.

Efficient Electrocatalytic Oxidation of Glycerol via Promoted OH* Generation over Single-Atom-Bismuth-Doped Spinel Co3O4

“…This peak is related to the nonhomogeneous charge contribution caused by the reaction between OH* and glycerol, which slowly shifts to a higher frequency and lower phase degree with raised potentials, as the white arrow shown in Figure B. From 1.30 V vs RHE, the peaks are located at the middle-frequency region (10 0 to 10 2 Hz), assigned with Co Td 2+ oxidation accompanied by OH* generation, according to Wang’s and Liu’s reports. , The generated OH* species can serve as active species to attack on the nucleophilic substrate, namely, glycerol, via direct oxidation. , …”

“…It was previously reported that nucleophilic substrates could also be oxidized through the chemical reaction with (oxy)­hydroxides such as cobalt oxyhydroxide (CoOOH) via an indirect oxidation mechanism. , To rule out the possibility that Co 3 O 4 and Bi-Co 3 O 4 may reconstruct to (oxy)­hydroxides during Co Td 2+ oxidation, in situRaman spectroscopies were performed. In the OER, a peak at ∼560 cm –1 was observed, attributed to the formation of CoOOH (Figures S35A and S36A).…”

“…While for Bi-Co 3 O 4 , the current density decreases at higher c (glycerol). This is because that stronger adsorption of glycerol over Bi-Co 3 O 4 would deprive of the locally adsorbed OH* species. , As a result, the enhanced coadsorptions of OH* and glycerol were observed over Bi-Co 3 O 4 , which accounts for its superior GOR performance compared with Co 3 O 4 .…”

“…49,50 The generated OH* species can serve as active species to attack on the nucleophilic substrate, namely, glycerol, via direct oxidation. 51,52 It was previously reported that nucleophilic substrates could also be oxidized through the chemical reaction with (oxy)hydroxides such as cobalt oxyhydroxide (CoOOH) via an indirect oxidation mechanism. 52,53 To rule out the possibility that Co 3 O 4 and Bi-Co 3 O 4 may reconstruct to (oxy)hydroxides during Co Td 2+ oxidation, in situRaman spectroscopies were S7 and S8), suggesting enhanced intrinsic catalytic activity due to single-atom Bi doping.…”

“…51,52 It was previously reported that nucleophilic substrates could also be oxidized through the chemical reaction with (oxy)hydroxides such as cobalt oxyhydroxide (CoOOH) via an indirect oxidation mechanism. 52,53 To rule out the possibility that Co 3 O 4 and Bi-Co 3 O 4 may reconstruct to (oxy)hydroxides during Co Td 2+ oxidation, in situRaman spectroscopies were S7 and S8), suggesting enhanced intrinsic catalytic activity due to single-atom Bi doping. Then the effect of glycerol concentration on GOR was investigated (Figure 4C,D).…”