In recent years, there has been a great interest in the conversion from agricultural waste to high value‐added chemicals. Citrus peel is a low‐cost and widely available waste resource that can be derived during citrus processing. In this study, we analyzed the composition of typical citrus peel and its hydrolysate. The hydrothermal conversion of citrus peel in different reaction conditions was also studied, and the optimum conditions for the preparation of levulinic acid and furfural were obtained. The maximum yield of levulinic acid was 21.9 wt% obtained in pure water, and the maximum yield of furfural was 9.1 wt% obtained in the water‐DMSO solvent mixture. With the increase in the reaction temperature, the yield of furfural decreased while the yield of levulinic acid increased.

The use of carbon-based catalysts to catalyze the hydrothermal conversion of biomass and its derived carbohydrates to produce platform compounds such as 5-(hydroxymethyl)­furfural (HMF), levulinic acid (LA), and furfural (FF) has a long history. The excellent thermal stability and chemical activity and low preparation cost of carbon-based catalysts make them develop rapidly in catalytic hydrothermal conversion, which is the core attention in the review. Carbon catalysts are divided into sulfuric acid-based carbon catalysts, phosphoric acid-based carbon catalysts, metal-supported carbon catalysts and other types of carbon catalysts, to study their application to hydrothermal decomposition of monosaccharides, disaccharides, polysaccharides, and biomass. The characteristics of different types of carbon catalysts were introduced. The diversified development of carbon-based catalysts and the upgrading of feedstocks have promoted the improvement of product selectivity, cost, and energy optimization, realizing the transformation of hydrothermal decomposition of biomass into a greener process. However, the development of efficient catalytic systems for hydrothermal conversion of abundant, cheap, and readily available biomass sources is still an ideal choice to expand the process strategy.