Hydrolysis Catalysis of <i>Miscanthus</i> Xylan to Xylose Using Weak-Acid Surface Sites
- Publication date
- Publisher
Abstract
Adsorption
and hydrolysis of xylan polysaccharides extracted from <i>Miscanthus</i> 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 <i>Miscanthus</i> 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