Direct conversion of cellulose to glucose and valuable intermediates in mild reaction conditions over solid acid catalysts

The direct hydrolysis of cellulose to glucose, HMF and other soluble by-products at 190 °C in water solution using zeolites (H-BEA, H-MOR), sulphated zirconia supported over mesoporous silica (SBA-15), Amberlyst®15, heteropolyacids and AlCl3·6H2O as acid catalysts was studied using a high cellulose to catalyst ratio (10), not-pretreated (neither mechanically nor chemically) cellulose and a static (not mixed) autoclave. Under these conditions, not usually considered, but relevant for industrial applications, micro and mesoporous solid acid catalysts are active in the direct hydrolysis of cellulose to glucose, HMF and other soluble by-products. The reactivity in crystalline cellulose conversion is determined on one side from the need to realize an efficient solid–solid interaction between the external surface of the catalyst and the crystalline cellulose, and on the other side on the need to limit the secondary reactions of the formed products. Microporous materials, due to the presence of shape-selectivity effects limiting the polymerization of glucose to humic-type species show the highest formation of glucose and HMF with respect to the sulphated zirconia supported over mesoporous silica (SBA-15) and homogeneous heteropoly acids.

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► The direct hydrolysis of cellulose to valuable products was performed under mild conditions.
► Mild conditions, relevant for industrial applications, allow the direct hydrolysis of cellulose to glucose, HMF and other soluble by-products on micro and mesoporous solid acid catalysts.
► An efficient solid-solid interaction between the external surface of the catalyst and the crystalline cellulose is a key factor for the conversion of cellulose.
► The presence of shape-selectivity effects in microporous catalysts limits the polymerization of glucose to humic-type species and determines the best formation of glucose and HMF with respect to mesoporous silica and homogeneous heteropoly acids.