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γ-Valerolactone (GVL) is an important bio-derived platform molecule whose atom- and energy efficient, and scalable, catalytic synthesis is highly desirable. Catalytic transfer hydrogenation (CTH) of ethyl levulinate (EL) to γ-valerolactone (GVL) has been selectively performed in batch and continuous flow over ZrO2/SBA-15 solid acid catalysts. Tuning the zirconia adlayer delivered maximum CTH activity for 11.6 wt% Zr, ascribed to the optimal ratio of Lewis and Brønsted acid sites for the two-step cascade reaction. EL conversion almost doubled under flow versus batch operation, accompanied by a small rise in selectivity to GVL, tripling average GVL productivity in continuous flow (5.2 vs. 1.37 mmol g−1 h−1). Turnover frequency (TOF) is significantly improved under flow conditions (14.5 h−1) relative to batch (3.6 h−1), demonstrating the utility of flow chemistry for accelerating the manufacture of valuable bio-derived molecules.

BACKGROUND: Modern day scientific endeavour strives towards global sustainability through the smart utilisation of renewable resources as base materials for chemicals. Until now, the most common commercial process to produce levulinic acid (a mass-produced platform chemical) depends on a two-stage mineral acid-catalysed reaction, which generates harmful environmental waste. In this work, an environmentally friendly levulinic acid production route using less harmful organic acids assisted by microwave heating from biomass feedstocks is reported for the first time. RESULTS: Using aluminum sulfate as a green Lewis acid catalyst and seven organic acids, levulinic acid was successfully produced from barley straw under microwave heating, with maleic acid giving the highest catalytic conversion. A Response Surface Methodology (RSM) approach was used to rapidly and effectively examine the effect of five reaction variables on the productivity of the levulinic acid. A wide range of different biomass wastes (barley straw, brewery waste, olive cake, spent tea leaves and potato, tomato, and mandarin peels) were subsequently screened to produce the levulinic acid. The highest yield of 86 wt% based on cellulose content from mandarin peel (a value comparable to a lengthier ‘non-green’ route) was achieved under the following optimized reaction conditions: 180 °C, 38 min, 2 M maleic acid concentration, 0.1 g Al 2(SO 4) 3 and 1:22 biomass: maleic acid ratio (g mL −1). CONCLUSIONS: The proposed method is a promising new route towards the green, high yield production of levulinic acid from a variety of agricultural and household lignocellulosic biomass wastes, without the need for pre-treatment.

Hierarchical Cu2O nanospheres with a Pompon Dahlia‐like morphology were prepared by a one‐pot synthesis employing electrostatic self‐assembly. Nanocomposite analogues were also prepared in the presence of reduced graphene oxide (rGO). Photophysical properties of the hierarchical Cu2O nanospheres and Cu2O/rGO nanocomposite were determined, and their photocatalytic applications evaluated for photocatalytic 4‐chlorophenol (4‐CP) degradation and H2 production. Introduction of trace (6 h continuous reaction is observed.

Fast pyrolysis bio‐oils possess unfavorable physicochemical properties and poor stability, in large part, owing to the presence of carboxylic acids, which hinders their use as biofuels. Catalytic esterification offers an atom‐ and energy‐efficient route to upgrade pyrolysis bio‐oils. Propyl sulfonic acid (PrSO3H) silicas are active for carboxylic acid esterification but suffer mass‐transport limitations for bulky substrates. The incorporation of macropores (200 nm) enhances the activity of mesoporous SBA‐15 architectures (post‐functionalized by hydrothermal saline‐promoted grafting) for the esterification of linear carboxylic acids, with the magnitude of the turnover frequency (TOF) enhancement increasing with carboxylic acid chain length from 5 % (C3) to 110 % (C12). Macroporous–mesoporous PrSO3H/SBA‐15 also provides a two‐fold TOF enhancement over its mesoporous analogue for the esterification of a real, thermal fast‐pyrolysis bio‐oil derived from woodchips. The total acid number was reduced by 57 %, as determined by GC×GC–time‐of‐flight mass spectrometry (GC×GC–ToFMS), which indicated ester and ether formation accompanying the loss of acid, phenolic, aldehyde, and ketone components.

A novel magnetic SO4/Fe-Al-TiO2 solid acid catalyst was synthesized for biodiesel production via the (trans)esterification of waste cooking oil (WCO). The nanocomposite catalyst was prepared by the sequential functionalisation of commercial rutile/anatase mixed phase TiO2 nanoparticles (NPs) with alumina as a buffer layer, and subsequently hematite to impart magnetic character, prior to sulfation with chlorosulfonic acid to introduce Brønsted acidity. XRD showed that the SO4/Fe-Al-TiO2 catalyst comprised titania (rutile and anatase phases), aluminium sulphate, and hematite nanoparticles, while electron microscopy revealed the layer-by-layer assembly of these components within the SO4/Fe-Al-TiO2 catalyst. FTIR confirmed the presence of surface sulphate groups SO42- and S2O72-/S3O102-, creating a predominantly Brønsted acid catalyst with high acid loading. The catalyst achieved 96 % fatty acid methyl ester (FAME) yield from WCO after 2.5 h of reaction at 90 °C, using 3 wt% of the magnetic catalyst, and a methanol:oil molar ratio of 10:1. SO4/Fe-Al-TiO2 was also effective for feedstocks containing up to 20 wt% of free fatty acid (FFA), and showed excellent stability for WCO (trans)esterification over 10 recycles.

Crude pyrolysis bio-oil contains significant quantities of carboxylic acids which limit its utility as a biofuel. Vapour phase ketonisation of organic acids contained within biomass fast-pyrolysis vapours offers a potential pre-treatment to improve the stability and energy content of resulting bio-oils formed upon condensation. Zirconia is a promising catalyst for such reactions, however little is known regarding the impact of thermal processing on the physicochemical properties of zirconia in the context of their corresponding reactivity for the vapour phase ketonisation of acetic acid. Here we show that calcination progressively transforms amorphous Zr(OH)4 into small tetragonal ZrO2 crystallites at 400 °C, and subsequently larger monoclinic crystallites >600 °C. These phase transitions are accompanied by an increase in the density of Lewis acid sites, and concomitant decrease in their acid strength, attributed to surface dehydroxylation and anion vacancy formation. Weak Lewis acid sites (and/or resulting acid-base pairs) are identified as the active species responsible for acetic acid ketonisation to acetone at 350 °C and 400 °C, with stronger Lewis acid sites favouring competing unselective reactions and carbon laydown. Acetone selectivity is independent of acid strength.

Functionalization of mesoporous SBA-15 frameworks by transition metal oxides offers a flexible route to fabricate new heterogeneous catalysts. Here, an inorganic-organic hybrid nanoporous catalyst H5PW10V2O40@VOx/SBA-15-NH2, was prepared and utilized as an efficient, eco-friendly, and recyclable catalyst for the one-pot, multi-component synthesis of 3-substituted indoles by indole substitution with aldehydes and malononitrile under solvent-free conditions. Catalysts were prepared by the non-covalent attachment of H5PW10V2O40 to a 3 wt%VOx/SBA-15 nanoporous support through a 3-(triethoxysilyl)propylamine linker. VOx/SBA-15 was prepared by a one-pot hydrothermal synthesis from TEOS and vanadium(V) oxytri-tert-butoxide [VO(O-tBu)3]. The resulting H5PW10V2O40@VOx/SBA-15-NH2 material was characterized by bulk and surface analysis including N2 porosimetry, FE-SEM, XRD, XPS, FT-IR, TGA-DTA, UV–Vis and ICP-OES, evidencing retention of the heteropolyacid Keggin structure. H5PW10V2O40@VOx/SBA-15-NH2 exhibits high activity and excellent yields (70–95%) of 3-substituted indoles under mild conditions, with negligible deactivation.

γ-valerolactone (GVL) is an important intermediate chemical with a wide range of applications as fuel, fuel additive and as a green solvent which has received a great deal of attentions from both academia and industry. This review aims to summarise the advances in conversion of renewable feedstocks into GVL through heterogeneous catalytic transfer hydrogenation (CTH) with a strong emphasis on discussing preparation, characterisation and performance of the catalysts in order to provide a better understanding of various catalytic systems and also to compare them in terms of catalytic performance.