Catalytic mechanisms of oxygen-containing groups over vanadium active sites in an Al-MCM-41 framework for production of 2,5-diformylfuran from 5-hydroxymethylfurfural

摘要

V-containing catalysts exhibit good catalytic performance toward the selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF). Here, we report our study on the catalytic mechanism of -(SiO)(3)V(O) ([V-0]) and -(SiO)(2)V(O)(OH) ([V-1]) on a V-doped Al-MCM-41 pore model (V/Al-MCM-41) for the aerobic oxidation of HMF to DFF. For the two active sites, there are three types of oxygen-containing functional groups, which are hydroxyl-oxygen ([V-OH]), lattice-oxygen ([V-O-Si]), and terminal-oxygen ([VO]). We show that the catalytic cycle involves two HMF molecules, and there are mainly two activation steps, i.e., both O-H and C-H bond cleavages of HMF, and the rate-determining step is associated with the C-H bond cleavage of the first HMF molecule. We illustrate the efficiency of the catalytic contribution as [V-OH] > [V-O-Si] > [VO], and the [V-1] active site with a hydroxyl group displays higher catalytic activity than the [V-0] active site without a hydroxyl group. The present study not only brings an in-depth understanding of the activation of both O-H and C-H bonds which has been proposed based on experimental results for biomass molecules, but also makes one step forward toward the mechanism-guided design and synthesis of efficient, environmentally-friendly, and low temperature recyclable heterogeneous catalysts.