This study presents a synergistic
catalytic system using the combination
of Brønsted hydrothermal carbon-based acid (HTCG-SO3H) and Lewis acid catalysts for one-pot conversion of cellulose to
levulinic acid (LA). Chromium chloride (CrCl3), among a
number of other Lewis acidic metal chlorides, was found to give the
highest LA yields, and was therefore used in combination with the
HTCG-SO3H, for cellulose conversion to LA. With the appropriate
amount of HTCG-SO3H, the formation of side products could
be reduced, resulting in improved selectivity of LA. Compared with
that obtained by CrCl3 alone, at 5 wt % HTCG-SO3H, 0.015 M CrCl3, 200 °C and 5 min reaction time,
the LA yield was considerably enhanced from 30 wt % to 40 wt %. Since
HTCG-SO3H is a heterogeneous catalyst that can be easily
prepared from biomass at moderate temperature, its use in such combined
catalyst system offers economic and environmental benefits, thus making
large-scale implementation of such process potentially feasible.
An acetal protection strategy for 5-hydroxymethylfurfural (HMF) was used to obtain 2,5-diformyfuran (DFF) using concentrated HMF solutions and a γ-Al 2 O 3 -supported Ru catalyst (Ru/γ-Al 2 O 3 ). The HMF-acetal with 1,3-propanediol can be oxidized to DFFacetal with a yield of 84.0 % at an HMF conversion of 94.2 % from a 50 wt % solution. In contrast, aerobic oxidation of nonprotected HMF using a 10 wt % solution afforded DFF only in a moderate yield (52.3 %). Kinetic studies indicated that the six-membered ring acetal group not only prevents side reactions but also accelerates aerobic oxidation of the À CH 2 OH moiety to À CHO under retention of the acetal functionality. Organic deposits formed during the reaction explained the significant decrease in the activity of the Ru/γ-Al 2 O 3 catalyst, which could be recovered neither by washing in water or organic solvents, nor by a calcination-reduction treatment. Sonication of the used Ru/γ-Al 2 O 3 catalyst in an aqueous NaOH solution successfully removed the deposits and allowed reuse of the catalyst for at least four times without activity loss.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.