Hydrolysis of cellulose into glucose by magnetic solid acid.

Cellulose is the major component of plant biomass, which is readily available and does not compete with the food supply. Hydrolysis of cellulose as the entry point of biorefinery schemes is an important process for chemical and biochemical industries based on sugars, especially for fuel ethanol production. However, cellulose not only provides a renewable carbon source, but also offers challenges to researchers due to the structural recalcitrance. Considerable efforts have been devoted to the study of hydrolysis of cellulose by enzymes, acids, and supercritical water. Recently, acid-catalyzed hydrolysis has attracted increasing attention. To overcome resistance to degradation through breaking hydrogen bonds and b-1,4glycosidic bonds, ionic liquids have been employed to form homogeneous solutions of cellulose prior to hydrolysis. Although the homogeneous hydrolysis can be carried out under mild conditions with a high glucose yield, the workup for separation of sugars, dehydrated products, and unreacted cellulose from the ionic liquid is normally difficult. 5] Hydrolysis of cellulose in diluted acids has been practiced for a long time. However, acid-waste generation and corrosion hazards are significant drawbacks of this process. To move towards more environmentally sustainable approaches, Onda et al. demonstrated that sulfonated activated carbon can convert amorphous ball-milled cellulose into glucose with a yield of 41%. Almost simultaneously, Hara et al. completely hydrolyzed cellulose to water soluble b-1,4-glucans at 100 8C using a more robust sulfonated activated carbon catalyst. Hydrolysis of cellobiose and cellulose catalyzed by layered niobium molybdate was achieved by Takagaki et al. , athough the yield of glucose from cellulose was low. Fukuoka et al. found that mesoporouscarbon-supported Ru catalysts were also able to catalyze the hydrolysis of cellulose into glucose. More recently, sulfonated silica/carbon cellulose hydrolysis catalysts were synthesized by Jacobs et al. , affording glucose in 50% yield. Zhang et al. employed sulfonated carbon with mesoporous structure for hydrolysis of cellulose, giving a glucose yield of 75%, which is the highest recorded yield on a solid acid. Considering the real biomass components and practical process for glucose production, two challenges remain for a catalytic system. Firstly, solid catalysts should be readily separated from the solid residues. Although cellulose can be converted almost completely in some cases, 11] lignin components can not be converted and humins are formed sometimes as solid residues. Secondly, to achieve a high yield of glucose, the reaction was usually conducted at low cellulose/liquid ratio (ca. 1:100). However, concentration of the glucose solution, prior to the production of ethanol or other compounds, is energy-consuming. Thus effective treatment of high cellulose loadings is required. In view of the importance of the cellulose/liquid ratio, Jacobs et al. carried out hexitol production from concentrated cellulose with heteropoly acid and Ru/C. We designed and synthesized a magnetic solid acid catalyst for the hydrolysis of cellulose at high cellulose/liquid ratio (1:10 or 1:15; Scheme 1). Sulfonic acid-functionalized mesopo-