Influence of Lewis and Brønsted acidic sites on graphitic carbon nitride catalyst for aqueous phase conversion of biomass derived monosaccharides to 5-hydroxymethylfurfural

Conversion of saccharides to 5-hydroxymethylfurfural is one of the fundamental steps in the synthesis of biodiesel. In this work, we report on the influence of Lewis and Brønsted acidic sites on metal-free graphitic carbon nitride catalysts for the conversion of monosaccharides to 5-hydroxymethylfurfural. We have examined the Lewis acidic sites by doping boron onto graphitic carbon nitride, and under optimal conditions, a maximal 91% yield of 5-hydroxymethylfurfural has been obtained from fructose. Subsequently, the boron doped graphitic carbon nitride was functionalized with Brønsted acidic group to prepare sulfonic acid functionalized boron doped graphitic carbon nitride, which possesses both Lewis and Brønsted acidic sites. However, the use of sulfonic acid functionalized boron doped graphitic carbon nitride as catalyst resulted in a lower yield (78%) of 5-hydroxymethylfurfural from fructose. In addition, time-dependent nuclear magnetic resonance spectroscopic study, temperature-programmed desorption study, and green metrics calculations have been performed to substantiate our findings. Overall, this work provides valuable insights on the influence of Lewis and Brønsted acidic sites on graphitic carbon nitride for biomass conversion reactions.