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The acetate fraction is the fourth most abundant fraction by weight in many plant species and can be easily extracted as acetic acid in high yields. We have previously shown that acetic acid obtained from steam pretreated beech wood could be upgraded in a single step into a mixture of cycloalkenes and aromatics suitable for use as an aviation fuel additive. In this work, we developed and validated a reaction network of this process by performing a detailed kinetic study. Specifically, a network kinetic model along with experimental data was used to estimate the kinetic and adsorption equilibrium parameters of the main reactions in our simplified reaction mechanism. Analysis of the experimental data and the proposed model and parameters provided insight into the reaction network and the process conditions required for optimal operation.

The development of sustainable plastics from abundant renewable feedstocks has been limited by the complexity and efficiency of their production, as well as their lack of competitive material properties. Here we demonstrate the direct transformation of the hemicellulosic fraction of non-edible biomass into a tricyclic diester plastic precursor at 83% yield (95% from commercial xylose) during integrated plant fractionation with glyoxylic acid. Melt polycondensation of the resulting diester with a range of aliphatic diols led to amorphous polyesters (Mn= 30–60 kDa) with high glass transition temperatures (72–100 °C), tough mechanical properties (ultimate tensile strengths of 63–77 MPa, tensile moduli of 2,000–2,500 MPa and elongations at break of 50–80%) and strong gas barriers (oxygen transmission rates (100 µm) of 11–24 cc m−2day−1bar−1and water vapour transmission rates (100 µm) of 25–36 g m−2day−1) that could be processed by injection moulding, thermoforming, twin-screw extrusion and three-dimensional printing. Although standardized biodegradation studies still need to be performed, the inherently degradable nature of these materials facilitated their chemical recycling via methanolysis at 64 °C, and eventual depolymerization in room-temperature water.

The hydroxide exchange membrane fuel cell (HEMFC) is a promising energy conversion technology but is limited by the need for platinum group metal (PGM) electrocatalysts, especially for the hydrogen oxidation reaction (HOR). Here we report a Ni-based HOR catalyst that exhibits an electrochemical surface area-normalized exchange current density of 70 μA cm–2, the highest among PGM-free catalysts. The catalyst comprises Ni nanoparticles embedded in a nitrogen-doped carbon support. According to X-ray and ultraviolet photoelectron spectroscopy as well as H2chemisorption data, the electronic interaction between the Ni nanoparticles and the support leads to balanced hydrogen and hydroxide binding energies, which are the likely origin of the catalyst’s high activity. PGM-free HEMFCs employing this Ni-based HOR catalyst give a peak power density of 488 mW cm–2, up to 6.4 times higher than previous best-performing analogous HEMFCs. This work demonstrates the feasibility of efficient PGM-free HEMFCs.

We explore the selective electrocatalytic hydrogenation of lignin monomers to methoxylated chemicals, of particular interest, when powered by renewable electricity. Prior studies, while advancing the field rapidly, have so far lacked the needed selectivity: when hydrogenating lignin-derived methoxylated monomers to methoxylated cyclohexanes, the desired methoxy group (−OCH3) has also been reduced. The ternary PtRhAu electrocatalysts developed herein selectively hydrogenate lignin monomers to methoxylated cyclohexanes—molecules with uses in pharmaceutics. Using X-ray absorption spectroscopy and in situRaman spectroscopy, we find that Rh and Au modulate the electronic structure of Pt and that this modulating steers intermediate energetics on the electrocatalyst surface to facilitate the hydrogenation of lignin monomers and suppress C–OCH3bond cleavage. As a result, PtRhAu electrocatalysts achieve a record 58% faradaic efficiency (FE) toward 2-methoxycyclohexanol from the lignin monomer guaiacol at 200 mA cm–2, representing a 1.9× advance in FE and a 4× increase in partial current density compared to the highest productivity prior reports. We demonstrate an integrated lignin biorefinery where wood-derived lignin monomers are selectively hydrogenated and funneled to methoxylated 2-methoxy-4-propylcyclohexanol using PtRhAu electrocatalysts. This work offers an opportunity for the sustainable electrocatalytic synthesis of methoxylated pharmaceuticals from renewable biomass.

Thanks to chemical stabilization, aldehyde-assisted fractionation (AAF) of lignocellulosic biomass has recently emerged as a powerful tool for the production of largely uncondensed lignin. Depolymerization of AAF lignin via ether cleavage provides aromatic monomers at near theoretical yields based on ether cleavage and an oligomeric fraction that remains largely unexploited despite its unique material properties. Here, we present an in-depth analytical characterization of AAF oligomers derived from hardwood and softwood in order to elucidate their molecular structures. These bioaromatic oligomers surpass technical Kraft lignin in terms of purity, solubility, and functionality and thus cannot even be compared to this common feedstock directly for material production. Instead, we performed comparative experiments with Kraft oligomers of similar molecular weight (Mn ∼ 1000) obtained through solvent extraction. These oligomers were then formulated into polyurethane materials. Substantial differences in material properties were observed depending on the amount of lignin, the botanical origin, and the biorefining process (AAF vs Kraft), suggesting new design principles for lignin-derived biopolymers with tailored properties. These results highlight the surprising versatility of AAF oligomers towards the design of new biomaterials and further demonstrate that AAF can enable the conversion of all biomass fractions into value-added products.

Lignin is one of the most promising sources of renewable aromatic hydrocarbons. Current methods for its extraction from lignocellulosic biomass—which include the kraft, sulfite, and organosolv processes—result in the rapid formation of carbon–carbon bonds, leading to a condensed lignin that cannot be effectively depolymerized into its constituent monomers. Treatment of lignocellulosic biomass with aldehydes during lignin extraction generates an aldehyde-stabilized lignin that is uncondensed and can be converted into its monomers at near-theoretical yields. Here, we outline an efficient, reproducible, and scalable process for extracting and purifying this aldehyde-stabilized lignin as a solid, which can easily be re-dissolved in an organic solvent. Upon exposure to hydrogenolysis conditions, this material provides near-theoretical yields of aromatic monomers (~40–50% of the Klason lignin for a typical hardwood). Cellulose and hemicellulose are also efficiently fractionated. This protocol requires 6–7 h for the extraction of the stabilized lignin and a basic proficiency in synthetic chemistry.

H-ZSM-5 zeolite has been shown to be an active catalyst for the synthesis of polyoxymethylene dimethyl ethers (OME). However, we demonstrated – by passivation of the zeolite's external surface – that the reaction rate is limited due to severe internal diffusion limitations of the reactants and products. External acid sites thus played a more prominent role in the observed overall reaction rate compared to the acid sites in the zeolite's micropores. Through controlled introduction of an intercrystalline network of mesopores the zeolite's activity was significantly enhanced by allowing a more significant part of the reaction to take place within the zeolite's micropores. By optimising alkaline treatment and consequent acid wash of H-ZSM-5, we achieved a two-fold increase in the initial reaction rate and a 10% increase in selectivity towards OME with 3 to 5 oxymethylene units (OME3–5), which are the more desirable products.

Polysaccharide depolymerization is an essential step for valorizing lignocellulosic biomass. In inexpensive systems such as pure water or dilute acid mixtures, carbohydrate monomer degradation rates exceed hemicellulose—and especially cellulose—depolymerization rates at most easily accessible temperatures, limiting sugar yields. Here, we use a reversible stabilization of xylose and glucose by acetal formation with formaldehyde to alter this kinetic paradigm, preventing sugar dehydration to furans and their subsequent degradation. During a harsh organosolv pretreatment in the presence of formaldehyde, over 90% of xylan in beech wood was recovered as diformylxylose (compared to 16% xylose recovery without formaldehyde). The subsequent depolymerization of cellulose led to carbohydrate yields over 70% and a final concentration of ~5?wt%, whereas the same conditions without formaldehyde gave a yield of 28%. This stabilization strategy pushes back the longstanding kinetic limits of polysaccharide depolymerization and enables the recovery of biomass-derived carbohydrates in high yields and concentrations.

Atomic layer deposition (ALD) and chemical layer deposition (CLD) are techniques to produce conformal, atomically precise overcoats for materials in gas and liquid phases, respectively. Although it is a challenge to explicitly model ALD/CLD dynamics because of the large timescales involved, a combination of rule-based deposition actions, followed by molecular dynamics relaxations, can capture the net effect of one cycle. For ALD, we developed deposition rules for the trimethylaluminum (TMA)/H2O system over Al2O3and SiO2substrates. We also explore the CLD system of Al(O-sec-Bu)3/H2O solvated in 2-butanol over an Al2O3substrate. In contrast to previous studies focusing on ligand exchange reactions, the gas-phase simulations predict that a TMA dissociation mechanism is the dominant growth mode, whereas the CLD simulations show a primary growth mode of deposition through precipitation of species that have already undergone reactions in solution. Together, these modeling results constitute a refinement of preexisting ALD models, leading to more accurate growth rate predictions, as well as a first step toward modeling more challenging liquid-phase processes.

A new studyopens a route to convert lignin, the world largest natural source of aromatics, into valuable bioactive compounds.

Realistically replacing petroleum-based plastics will require efficient routes to performance polymers using scalable processes from abundantly available lignocellulosic biomass. We surveyed academic and patent literature for processes in the latest stages of commercial development to draw out design strategies that have enabled their success. We found that these processes consist of chemocatalytic transformations of non-edible biomass to rigid plastic precursors with high drop-in readiness via a stable, hydrophobic, and distillable platform molecule. However, due to the deoxygenated nature of these precursors, the processes suffer from low biomass utilization efficiency and high process complexity–thereby limiting their sustainability. We discuss our group's preliminary efforts to design novel monomers with lower drop-in readiness, but with increased process efficiency and simplicity from biomass.

The cleavage of β-O-4 linkages in lignin can generate monomers with a phenyl propane structure that can easily be upgraded into valuable hydrocarbon biofuels and renewable aromatic chemicals. High-yield lignin monomer production from extracted (or technical) lignin that is produced in a practical way could facilitate the productivity and profitability of biomass conversion processes. However, interunit carbon–carbon (C–C) linkages present in native lignin or formed during lignin condensation in biomass pretreatments dramatically reduce lignin monomer yields. Here, we present a perspective on biological and chemical strategies that have been successfully used to reduce the formation of C–C linkages in native or technical lignin. We analyze the mechanisms involved in these strategies and offer our views on improving the quality of technical lignin resulting from biomass conversion in order to achieve high-yield lignin monomer production.

There are several methods to isolate near-native lignins, including milled-wood lignin, enzymatic lignin, cellulolytic enzyme lignin, and enzymatic mild-acidolysis lignin. Which one is the most representative of the native lignin? Herein, near-native lignins were isolated from different plant groups and structurally analyzed to determine how well these lignins represented their native lignin counterparts. Analytical methods were applied to understand the molecular weight, monomer composition, and distribution of interunit linkages in the structure of the lignins. The results indicated that either enzymatic lignin or cellulolytic enzyme lignin may be used to represent native lignin in softwoods and hardwoods. None of the lignins, however, appeared to represent native lignins in grasses (monocot plants) because of substantial syringyl/guaiacyl differences. Complicating the understanding of grass lignin structure, large amounts of hydroxycinnamates acylate their polysaccharides and, when released, are often conflated with actual lignin monomers.

•Ni-Ga on alumina shows high selectivity for CO in the RWGS reaction at 400 °C.•Addition of Ga results in improved dispersion of Ni on the support.•OH groups play a prominent role for the catalyst activity.•The reaction proceeds through bicarbonates and formates as intermediate products.

Introducing oligomeric or polymeric units into metal–organic frameworks (MOFs) can result in composites that have significantly improved properties when compared with the individual MOF or polymer building blocks. With such synergy in mind, this work presents the design of a novel MOF/polyazoamine support that is used to stabilize Pd nanoparticles (NPs). The resulting composite catalyst, tested in the reductive amination of levulinic acid, is found to have a markedly improved lifetime when compared to just the MOF or polymer support containing Pd. It is demonstrated, for the first time, that the lifetime enhancement stems directly from the polymer, which plays a dual role: (i) the oligomer stabilizes the MOF support through the elimination of certain vibrational modes associated with the framework ligand and likely pore-filling effects in the largest MOF pore and (ii) the Lewis base functionality on the oligomer backbone binds to the surface of the Pd NPs, thus, increasing their activity and inhibiting their aggregation. Several complementary spectroscopic (IR, X-ray photoelectron spectroscopy, Raman spectroscopy) and computational tools (pore space and topology analysis, molecular mechanics, and density functional theory simulations) are used to describe the nature of the MOF–oligomer interaction and identify the most likely location of the polymer within the MOF pore.