Regulating the Alkalinity of Carbon Nitride by Magnesium Doping to Boost the Selective Isomerization of Glucose to Fructose

Brønsted base catalyzed isomerization of glucose toward fructose is on the rise due to the high value and versatility of fructose in biorefinery. Herein, we report the discovery of alkali- and alkaline-earth-metal-doped carbon nitride (C3N4) as base catalysts for the selective isomerization of glucose to fructose. The characterizations proved that introducing a small quantity of alkali and alkaline-earth metals into C3N4 can remarkably improve the amount of strong basic sites. Among the tested materials, Mg-doped C3N4 afforded an excellent fructose yield (>32%) and selectivity (>84%) from a high loading (10 wt %) of glucose in water at 80 °C with the lowest apparent activation energy (107 kJ mol–1), far exceeding that of the pristine C3N4 material. Although more efforts are required to improve the reusability, the proof of strong alkalinity and superior catalytic performance should greatly extend the applications of metal-doped C3N4 materials.