Nitrogen doped carbon spheres with wrinkled cages for the selective oxidation of 5-hydroxymethylfurfural to 5-formyl-2-furancarboxylic acid

Novel Challenges on the Catalytic Synthesis of 5-Hydroxymethylfurfural (HMF) from Real Feedstocks

The depletion of fossil resources makes the transition towards renewable ones more urgent. For this purpose, the synthesis of strategic platform-chemicals, such as 5-hydroxymethylfurfural (HMF), represents a fundamental challenge for the development of a feasible bio-refinery. HMF perfectly deals with this necessity, because it can be obtained from the hexose fraction of biomass. Thanks to its high reactivity, it can be exploited for the synthesis of renewable monomers, solvents, and bio-fuels. Sustainable HMF synthesis requires the use of waste biomasses, rather than model compounds such as monosaccharides or polysaccharides, making its production more economically advantageous from an industrial perspective. However, the production of HMF from real feedstocks generally suffers from scarce selectivity, due to their complex chemical composition and HMF instability. On this basis, different strategies have been adopted to maximize the HMF yield. Under this perspective, the properties of the catalytic system, as well as the choice of a suitable solvent and the addition of an eventual pretreatment of the biomass, represent key aspects of the optimization of HMF synthesis. On this basis, the present review summarizes and critically discusses the most recent and attractive strategies for HMF production from real feedstocks, focusing on the smartest catalytic systems and the overall sustainability of the adopted reaction conditions.

Crystal Faces-Tailored Oxygen Vacancy in Au/CeO2 Catalysts for Efficient Oxidation of HMF to FDCA

Developing an efficient catalyst to upgrade 5-hydroxymethylfurfural (HMF) to high-value-added downstream chemicals is of great significance in biomass conversion. Nanorod (110)-, nanocube (100)-, and nanooctaheron (111)-CeO₂ -supported Au nanoparticles were prepared to investigate the intrinsic effect of CeO₂ crystal faces on the oxidation of HMF to 2,5-furandicarboxylic acid (FDCA). The experimental results and density functional theory calculation revealed that the concentration of oxygen vacancy (V_O ) for exposed specific crystal faces was crucial to the oxygen adsorption ability, and Au/nanorod-CeO₂ with the highest V_O concentration promoted the formation of more oxygen active species (superoxide radical) on CeO₂ (110) crystal face than (100) and (111) crystal faces. Besides, the higher V_O concentration could provide a strong adsorption ability of HMF, greatly boosting the activation of HMF. Thus, these results led to a superior catalytic activity for HMF oxidation over Au/nanorod-CeO₂ (FDCA yield of 96.5 %). In-situ Fourier-transform (FT)IR spectroscopy uncovered the HMF oxidation pathway, and the possible catalytic mechanism was proposed. The deep insight into the role of regulation for crystal faces provides a basis for the rational design of highly active facets for the oxidation of HMF and related reactions.