Imidazole-Functionalized Polyoxometalate Catalysts for the Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran Using Atmospheric O2

Dan Liu; Baokuan Chen; Jie Li; Zhengguo Lin; Peihe Li; Ni Zhen; Yingnan Chi; Changwen Hu

doi:10.1021/acs.inorgchem.0c03698

Imidazole-Functionalized Polyoxometalate Catalysts for the Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran Using Atmospheric O₂

Inorg Chem. 2021 Mar 15;60(6):3909-3916. doi: 10.1021/acs.inorgchem.0c03698. Epub 2021 Feb 17.

Authors

Dan Liu¹, Baokuan Chen², Jie Li¹, Zhengguo Lin¹, Peihe Li¹, Ni Zhen¹, Yingnan Chi¹, Changwen Hu¹

Affiliations

¹ Key Laboratory of Cluster Science, Ministry of Education, Beijing Key Laboratory of Photoelectroic/Electrophotonic Conversion Materials, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081 P.R. China.
² School of Petrochemical Engineering, Liaoning Shihua University, Fushun, Liaoning 113001, P.R. China.

PMID: 33593056
DOI: 10.1021/acs.inorgchem.0c03698

Abstract

Biomass as a sustainable and abundant carbon source has attracted considerable attention as a potential alternative to petroleum resources. The selective oxidation of 5-hydroxymethylfurfural (HMF), a versatile platform molecule, to value-added 2,5-diformylfuran (DFF) provides an efficient pathway for biomass valorization. Herein, three discrete imidazole-functionalized polyoxometalates (POMs), HPMo₈V^VI₄O₄₀(V^VO)₂[(V^IVO)(IM)₄]₂·nH₂O·(IM)_m (IM = 1-methylimidazole, n = 4, m = 8 for 1; IM = 1-ethylimidazole, n = 4, m = 9 for 2; IM = 1-propylimidazole, n = 0, m = 4 for 3), have been successfully synthesized by a facile solvothermal method and thoroughly characterized by routine techniques. Compounds 1-3 contain a bi-capped pseudo-Keggin {HPMo₈V₄O₄₀(VO)₂} and two imidazole-functionalized {(VO)(IM)₄} groups, which, to our knowledge, represent the first examples of organic-functionalized Mo-V clusters. Compounds 1-3 as heterogeneous catalysts can effectively promote the transformation of HMF to DFF using atmospheric O₂ as oxidant. Under minimally optimized conditions, 95% of HMF was converted by 1 with 95% selectivity for DFF and its catalytic activity was basically maintained after five cycles. Moreover, the important roles of the bi-capped pseudo-Keggin cluster and the functionalized V groups in the selective oxidation of HMF have been explored. According to experimental and spectroscopic results, a three-step oxidation mechanism of HMF to DFF has been proposed.