Abstract
A series of biomass-derived platform molecules, such as glucose, furans, levulinic acid, 5-hydroxymethylfurfural, and acetic acids, can be converted into a variety of value-added chemicals through catalytic transformations that include dehydration, hydrogenation, oxidation, isomerization, reforming, ketonization, and aldol condensation over heterogeneous catalysts. Aqueous-phase processing is an important issue and a great challenge for the heterogeneous catalytic conversion of biobased chemicals due to the high water content of the biomass and the formation of water during the transformation process. In this paper, heterogeneous catalysts that are applicable to the aqueous-phase conversion process of biomass platform chemicals, including noble metal catalysts, non-noble metal catalysts, bimetallic catalysts, metal oxides, and zeolite, are introduced, and a comprehensive evaluation of the catalyst performance, including the catalytic activity, stability, and regeneration performance of different kinds of heterogeneous catalysts, are made. Besides, we highlighted the effect of water on heterogeneous catalysts and the deactivation mechanism in the aqueous phase. Beyond this, several catalytic mechanisms of aqueous-phase conversion over heterogeneous catalysts are summarized in order to help understand the reaction process on the surface of catalysts in the aqueous phase, so as to design targeted catalysts. At last, a prospect of biobased chemicals and fuels is forecasted.
Highlights
With the depletion of traditional fossil energy and its environmental adverse impact, alternative energy sources that have good renewability and environment friendliness are needed (Tang et al, 2017)
Though the direct pyrolysis or hydrothermal liquefaction of raw biomass as biofuels may be more competitive at present, it is undeniable that the aldol condensation of C5 or C6 platform chemicals has opened up a potential application route of upgrading the value of biomass and producing specific chemicals from biomass
With water as a solvent, the principles of green chemistry are better embodied in terms of the reaction and separation processes. Typical reactions such as dehydration, hydrogenation, oxidation, isomerization, reforming, ketonization, and aldol condensation have been introduced for a general conversion process of biomass
Summary
With the depletion of traditional fossil energy and its environmental adverse impact, alternative energy sources that have good renewability and environment friendliness are needed (Tang et al, 2017). The heterogeneous catalysts that are applied for the aqueous-phase conversion of biomass platform chemicals are usually porous materials with high surface activity and specific surface areas, such as alumina, silica, carbon materials, and metal oxides Because of the rehydration and polymerization reactions, many by-products, such as organic acids and humins, were synthesized in glucose dehydration to HMF in the water phase (Delidovich et al, 2014) In this part, we summarize recent advances in the heterogeneous reaction system for the catalytic production of furan compounds from dehydration of biomass platform chemicals (Wang et al, 2017). Mesoporous zeolites, due to their good structural feature, high surface area, and relatively large pore size, have been widely studied for the dehydration of biomass platform chemicals, such as glucose dehydration to HMF. The result for the reaction of the xylose conversion rate is 71.8% and the furfural yield is 28.8% in water at 150◦C for 16 h with Amberlyst 70 (specific surface area 36 m2 g−1 concentration of acid sites 2.65 mmol-H+ g−1, average pore diameter 22 nm) as the catalyst (Sato et al, 2019)
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