Hydrolysis Catalysis of Miscanthus Xylan to Xylose Using Weak-Acid Surface Sites

Abstract

Adsorption and hydrolysis of xylan polysaccharides extracted from Miscanthus biomass are demonstrated, using surface-functionalized MCN (mesoporous carbon nanoparticle) materials that comprise weak-acid sites, at a pH corresponding to biomass extract. Extracted xylan polysaccharides consist of a peak molecular weight of 2008 g/mol according to GPC (gel-permeation chromatography), corresponding to approximately 15 xylose repeat units, and, a calculated length of 7 nm and radius of gyration of 2.0 nm based on molecular dynamics simulations. A highly active material for the adsorption and depolymerization of xylan is a hydrothermally treated sulfonated MCN material, which consists of 90% weak-acid sites. In spite of the large polysaccharide size relative to its 1.6 nm pore radius, this material adsorbs up to 76% of xylan strands from extract solution, at a weight loading of 29% relative to MCN. Starting with a 9.7% xylose yield in Miscanthus extract, this material hydrolyzes extracted xylan to xylose, and achieves a 74.1% xylose yield, compared with 24.1% yield for the background reaction in acetate buffer, at 150°C for 4 h. Catalytic comparisons with other MCN-based materials highlight the role of confinement and weak-acid surface sites, and provide some correlation between activity and phenolic OH acid-site density. However, the lack of a directly proportional correlation between weak-acid site density and catalyzed hydrolysis rate signifies that only a fraction of weak-acid surface sites are catalytically active, and this is likely to be the sites that are present in a high local concentration on the surface, which would be consistent with previously observed trends in the hydrolysis catalysis of chemisorbed glucans on inorganic-oxide surfaces.The depolymerization of biomass-derived polymers into their monomeric components represents a grand challenge for enabling renewable approaches to fuels and chemicals. 1 We have recently demonstrated the hydrolysis of chemisorbed glucans that are grafted on inorganic-oxide surfaces, as an example of general-acid catalysis involving weak-acid OH defect sites in water. 2−4 We also demonstrated the rapid (transport time scale was faster than could be measured) adsorption of long-chain polysaccharides consisting of (1→4)-β-D-glucans to the interior surface of mesoporous carbon nanoparticle (MCN) materials, in spite of these polysaccharides being several-fold larger in radius of gyration than the MCN pore radius. 5 The affinity between the polysaccharide and the MCN surface was observed to increase with the molecular weight of the polymer, in a manner that was consistent with cumulative weak aromaticcarbohydrate interactions enthalpically driving adsorption, as observed previously in glycoproteins. 5 Based upon all of these data, we hypothesized that MCN materials may be able to catalyze the depolymerization of polysaccharides directly from biomass by relying exclusively on weak-acid surface sites. We rationalized such an approach to biomass-derived polysaccharide hydrolysis by ...

Integrated, Cascading Enzyme‐/Chemocatalytic Cellulose Conversion using Catalysts based on Mesoporous Silica Nanoparticles

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Depolymerization of Cellulosic Biomass Catalyzed by Activated Carbons

“…It was also found that the activity of K26 decreased by reducing the amount of oxygenated groups. We and Chung et al, respectively, showed that the catalytic activity of such carbons was maintained after treating the materials with sodium acetate/acetic acid buffer of pH 4.0-4.1 [ 14 ]. If the carbon catalysts were strong acids, they would be deactivated by the treatment due to ion exchange with Na + .…”

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