Recent Advances in Aqueous-Phase Catalytic Conversions of Biomass Platform Chemicals Over Heterogeneous Catalysts

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.

Catalytic Upgrading of Xylose to Furfuryl Alcohol over Zr-SBA-15

“…13,27 This approach was taken due to the mandatory presence of large amounts of water in biomass conversion processes at which catalysts are expected to operate since second generation sugars to be upgraded are made available as low-concentration hydrolysates. 3,42 Total acidity was indeed remarkably higher for all Zr-SBA-15 catalysts when contrasted to unmodified siliceous SBA-15 as presented in Table 1. Accordingly, it was noted that acidity increases along with the amount of Zr in the SBA-15 framework in line with other reports in the literature.…”

“…13 The constraints imposed by water in xylose conversion need to be dealt with though, since carbohydrates are usually available as low-concentration aqueous solutions (hydrolysates) in waste biomass fractionation processes. 3,42 Moreover, their solubility is limited in many organic solvents, requiring then at least some amount of water to allow liquidphase processes.…”

“…Altogether, these results presented so far disclose that the catalysts synthesized for this study are indeed well-ordered mesoporous SBA-15 type materials at which Zr 4+ species are inserted into the SiO 2 framework. Such incorporation is expected to generate acidity on the well reckoned nonacidic siliceous SBA-15 surface, and thus total acidity of all catalysts was estimated by titration. , This approach was taken due to the mandatory presence of large amounts of water in biomass conversion processes at which catalysts are expected to operate since second generation sugars to be upgraded are made available as low-concentration hydrolysates. , Total acidity was indeed remarkably higher for all Zr-SBA-15 catalysts when contrasted to unmodified siliceous SBA-15 as presented in Table . Accordingly, it was noted that acidity increases along with the amount of Zr in the SBA-15 framework in line with other reports in the literature .…”

Advances in Upgrading Biomass to Biofuels and Oxygenated Fuel Additives Using Metal Oxide Catalysts

“…Biomass derived fuels and additives cannot entirely replace the existing fossil-based fuels, − but they can be effectively used as components in various fuel blends with conventional fossil-based fuels, such as biodiesel and bioalcohols. Biodiesel production mainly involves transesterification of fats or oils with lower alcohols for the production of fatty acids methyl esters (FAMEs).…”

Novel Approach of Reusing the Precious Ru in the Wastewater Derived from the Depolymerization of Lignite to Prepare Ru–AC Catalysts Doped with Nb2O5

“…γ-Valerolactone (GVL) is considered as a green solvent, a potential fuel additive, and a precursor of valuable chemicals, which could be generated via the hydrogenation and lactonization of the biologically derived molecule levulinate acid (LA) and its esters such as ethyl levulinate (EL). So far, various nonprecious metal-based catalysts have been developed for the hydrogenation of EL to GVL, including Ni-, Cu-, Co-, Zr-, and Fe-based catalysts, − but the high metal content, high energy input, long reaction time, and issues concerning reusability in most nonprecious metal catalytic systems still need to be overcome. , On the contrary, precious metal catalysts, especially Ru-based catalysts, were found to be one of the best hydrogenation catalysts due to its excellent activity, selectivity, and stability . In recent years, Ru catalysts supported with a series of materials were applied for the hydrogenation of EL to GVL, including Ru/CeO 2, Ru/TiO 2, Ru/UiO-66, Ru/Zn-Al-Zr layered double hydroxide, etc.…”