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 (VO ) for exposed specific crystal faces was crucial to the oxygen adsorption ability, and Au/nanorod-CeO2 with the highest VO 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 VO 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.
Keywords: 5-hydroxymethylfurfural; CeO2; catalytic oxidation; crystal face; oxygen vacancy.
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