Weak‐Acid Sites Catalyze the Hydrolysis of Crystalline Cellulose to Glucose in Water: Importance of Post‐Synthetic Functionalization of the Carbon Surface

Abstract

The direct hydrolysis of crystalline cellulose to glucose in water without prior pretreatment enables the transformation of biomass into fuels and chemicals. To understand which features of a solid catalyst are most important for this transformation, the nanoporous carbon material MSC‐30 was post‐synthetically functionalized by oxidation. The most active catalyst depolymerized crystalline cellulose without prior pretreatment in water, providing glucose in an unprecedented 70 % yield. In comparison, virtually no reaction was observed with MSC‐30, even when the reaction was conducted in aqueous solution at pH 2. As no direct correlations between the activity of this solid–solid reaction and internal‐site characteristics, such as the β‐glu adsorption capacity and the rate of catalytic hydrolysis of adsorbed β‐glu strands, were observed, contacts of the external surface with the cellulose crystal are thought to be key for the overall efficiency.

Fabrication of weak‐acid functionalized mesoporous carbon solid acid from tannic acid and its use for saccharification of cellulose

“…To et al . using MSC‐30, a high surface‐area commercially available nanoporous material, also demonstrated the importance of oxidative surface functionalization of carbon catalyst. They were using HNO 3 and NaOCl solutions as oxidation agents.…”

“…To et al . suggested that local density of weak‐acid sites on the external surface of carbon catalyst can be in direct solid‐solid contact with the crystalline‐cellulose surface for catalyzing the depolymerization reaction. Hence, we tentatively propose that phenolic groups can form hydrogen bonds with hydroxyl groups in beta‐1,4‐glycosidic bonds of a cellulose chain and the adjacent carboxylic acids or hydroxyl groups have an opportunity to activate glycosidic bonds in the strands toward hydrolysis, by the same intramolecular general acid catalysis mechanism invoked by Capon .…”

“…To et al . developed nanoporous carbon catalysts that functionalized by weak‐acids using oxidation treatment in NaOCl and HNO 3 . Although the yield of glucose was high (70.0%), the ratio of catalyst/substrate used in the reaction was too high [catalyst/substrate: 20/1.5 (g/g)] and the time for hydrolysis was too long (24 h at 150°C followed by 3 h of hydrolysis at 180°C).…”

Heteropoly Acid-Based Catalysts for Hydrolytic Depolymerization of Cellulosic Biomass

“…As the most abundant source of biomass and one of the most widely distributed and abundant polysaccharides in nature, cellulose provides more possibilities for sustainable chemicals and fuels in the future (Huber et al, 2006;Climent et al, 2014;Sheldon, 2014;To et al, 2015). Hence, the conversion of cellulose could become a significant part of biomass utilization, which plays an important role in the development of chemicals and fuels in the future.…”

A novel route for green conversion of cellulose to HMF by cascading enzymatic and chemical reactions

“…However, due to its robust crystal structure with high chemical stability, depolymerization of cellulose through solid–solid interactions with solid synthetic catalysts requires substantial pretreatments, which remarkably increases the number of processing steps and hence the energy and environmental cost . Recently, inspired by the concept that weakly acidic and water‐tolerant carbons might be potentially useful for the hydrolysis of cellulose, carbon catalysts carrying weak‐acid sites (i.e., carboxylic and phenolic groups) have been synthesized and used for the decomposition of cellulose without pretreatment in water, providing appreciable glucose yield . Nevertheless, the reaction temperature of reported aqueous systems is still very high, and the yield of glucose is not satisfactory.…”