Chemocatalytic hydrolysis of cellulose into glucose over solid acid catalysts

With the progressive increase in global energy demands and the continuous depletion of worldwide fossil resources, renewable lignocellulosic biomass has attracted more and more attention. As the most abundant component of lignocellulosic biomass, cellulose, which is a linear polymer formed by the repeating connection of glucose units through β-1,4-glycosidic linkages, is considered to be an inexhaustible raw material for the sustainable production of chemicals and fuels. For the effective utilization of cellulose, the primary and essential step is the hydrolysis of cellulose into glucose. Although homogeneous acids and cellulases are the most common catalysts for the hydrolysis of cellulose into glucose, they possess a series of problems such as reactor corrosion, waste treatment and poor recyclability and high cost, low efficiency and long reaction time, respectively. In order to overcome the above-mentioned drawbacks, solid acid catalysts have been increasingly employed for the hydrolysis of cellulose into glucose in recent years. In this review, the state-of-the-art studies on the hydrolysis of cellulose into glucose over various types of solid acid catalysts such as acid resins, metal oxides, H-form zeolites, heteropoly acids, functionalized silicas, supported metals, immobilized ionic liquids, carbonaceous acids and magnetic acids are systematically summarized. Meanwhile, reaction medias, auxiliary methods and neoteric strategies for the hydrolysis of cellulose into glucose are intensively discussed. Furthermore, some potential research trends in the future are also prospected to provide some valuable ideas for the hydrolysis of cellulose into glucose in a more green, simple, efficient and inexpensive way.