Synthesis of MgO-doped ordered mesoporous carbons by Mg²⁺-tannin coordination for efficient isomerization of glucose to fructose

In-situ MgO-doped ordered mesoporous carbon (OMC@MgO) was fabricated by formaldehyde-free self-assembly method, in which biomass-derived tannin was used as carbon precursor replacing fossil-based phenolics, Mg²⁺ as both cross-linker and precursor of catalytic sites. Up to ∼20 wt% MgO could be doped in the carbon skeleton with good dispersion retaining well-ordered mesoporous structures, while more MgO content (35 wt%) led to the failing in the formation of ordered mesoporous structure. The OMC@MgO possessed a high specific surface area (298.8 m² g^-1), uniform pore size distribution (4.8 nm) and small crystallite size of MgO (1.73 nm) due to the confinement effect of ordered mesoporous structure. Using OMC@MgO as the heterogeneous catalyst, a maximum fructose yield of 32.4% with a selectivity up to 81.1% was achieved from glucose in water (90 ℃, 60 min), which is much higher than that obtained using the MgO doped active carbon via conventional post-impregnation method (26.5% yield with 58.3% selectivity). Higher reaction temperature (>90 ℃) resulted in decrease of selectivity due to the formation of humins. The designed OMC@MgO displayed tolerant to high initial glucose concentrations (10 wt%) and could remain good recyclability without significant loss of activity for three cycles.