Understanding Contributions of Silanols Over Ag/USY Catalysts in Selective Oxidation of 5-Hydroxymethylfurfural

The selective oxidation of 5-hydroxymethylfurfural (HMF) to value-added products plays an important role in biomass catalytic transformation, which essentially depends upon design of highly efficient and selective catalysts. This study aims to identify contributions of silanols (Si-OH groups) on Ag/USY catalysts to regulating catalytic performances in selective oxidation of HMF to HMFCA (5-hydroxymethyl-2-furancarboxylic acid), by means of aluminium tri-sec-butoxide (AlBO) modification to suppress Si-OH groups of USY and 2,6-di-tert-butylpyridine (2,6-DTBPy) selective poison to shield Brønsted acid sites in the reaction system. The catalysts are characterized by XRD, BET, TEM, XPS and FT-IR to examine the crystal structures, surface areas, porosity, morphology, Ag distribution, chemical states, and surface adsorptive properties. The HMF conversion (44-49.2%) slightly changes with increasing AlBO content, whereas the HMFCA selectivity gradually goes down from 56.2 to around 22.1% and the levulinic acid (LA) selectivity minorly raises from 5.6 to 12.8%. The production of LA originates from enhanced Brönsted acid sites after AlBO modification, and the decline of HMFCA selectivity is principally attributed to the suppression of Si-OH groups that weakens the interaction between HMF reactants and catalysts. This work provides new insights into the role of surface modification in tailoring metal and zeolite-based catalysts for organic conversions.

Graphical Abstract