Mechanistic Studies on the Photooxidation of 5‐Hydroxymethylfurfural by Polyoxometalate Catalysts and Atmospheric Oxygen

Abstract

Efficient oxidation of 5‐hydroxymethylfurfural (HMF) to corresponding furanic products represents an important research focus of biomass valorization, recent research on polyoxometalates (POMs)‐catalyzed aerobic oxidation of HMF usually requires high temperature and sometimes high O2/air pressure. In this work, we report a mild and green approach to photocatalytically transform HMF into various furanic products using atmospheric oxygen as oxidant and POMs as photocatalysts. The influence of different POMs, light sources, and additives were systematically investigated by various experimental and spectroscopic results. Under minimally optimized conditions, 88.0 % HMF can be efficiently photooxidized with as high as 70.2 % furanic yield by TBA‐W10 catalyst after 2 h irradiation of 365 nm UV light when coupling with TEMPO and Na2CO3 as additives. Finally, detailed mechanistic pathways of HMF photooxidation have been proposed to illustrate the transformation of HMF to various furanic products. This work provides some insightful guidelines for photooxidation of biomass‐derived platform chemicals to value‐added products under efficient, mild, and green conditions, exhibiting potential practical applications in the future.

Sunlight-driven photocatalytic conversion of furfural and its derivatives

“…105 As demonstrated in Fig. 15, • O 106 In conclusion, the addition of base additives and/or the use of organic solvents are often required to achieve better results in the photocatalytic selective oxidation of HMF to FDCA. Therefore, it is also necessary to further optimize the prepa- ration of catalysts and modulate the appropriate energy-band positions in anticipation of higher FDCA yield in the base-free and aqueous phase.…”

Control of selectivity in organic synthesis via heterogeneous photocatalysis under visible light

“…These valuable products can be applied in several fields such as polymers, pharmaceuticals and other functional materials (Fig. 8) [85]. In heterogeneous photocatalysis, different ROSs have been well utilized to control selectivity during the photo-oxidation of HMF [86].…”

Recent Advances in the Photocatalytic Conversion of Biomass-Derived Furanic Compounds

“…Polyoxometalates (POMs) have attracted extensive attention in recent years due to their adjustable acidity and redox performance, strong UV absorption capacity, and highly adjustable structure . In a report by Lv et al, 88.0% photooxidation efficiency of HMF can be obtained over the tetrabutylammonium (TBA) salt of the POM catalyst W 10 O 32 4– (denoted as TBA-W 10 ) using atmospheric oxygen as the oxidant and TEMPO and Na 2 CO 3 as additives under 365 nm ultraviolet light for 2 h. The yields of furanic compounds, including DFF, FDCA, HMFCA, and FFCA, reach 70.2%, and FFCA is the main product. The photooxidation activity of TBA-W 10 is signifantly enhanced by the synergistic effect of TEMPO and Na 2 CO 3 .…”