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Invited for this month's cover is the group of Bert M. Weckhuysen at the Utrecht University (The Netherlands). The cover picture shows an attenuated Total Reflection Infrared spectroscopy (ATR-IR) probe monitoring a chemical reaction in the liquid phase, particularly water, at demanding conditions. The light penetrates few microns deep in proximity of the ATR-IR probe and thus any IR-active entity in that range is probed. This research systematically addresses the challenges associated with acquiring operando ATR-IR spectra for liquid/aqueous phase reactions, which is essential for better understanding of chemical reactions in the liquid phase. Read the full text of their Full Paper at 10.1002/cmtd.202100041.

The Diels-Alder (DA) reaction of furans is a versatile tool in synthetic organic chemistry and in the production of sustainable building blocks and smart materials. Numerous experimental and theoretical investigations suggest that the diene scope is effectively limited to electron-rich furans, which excludes the most abundant and readily accessible renewable derivatives: furfural and its 5-hydroxymethyl homologue. Herein we show for the first time that electron-poor 2-formylfurans can also directly engage in Diels-Alder couplings. The key to success is the use of aqueous medium, which supplies an additional thermodynamic driving force by coupling the unfavorable DA equilibrium to the exergonic hydration of the carbonyl functionality in the adducts to form geminal diols. This finding enables the direct access to various novel DA adducts derived from renewable furfurals and maleimides, via a mild, simple and environmentally-friendly synthetic protocol.

PD was supported by a grant of the Netherlands Scientific Organization NWO 824.15.023 to RPdV. The Academy of Finland grant no. 308284 to MRM is acknowledged. Part of the research was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the Department of Energy's Office of Biological and Environmental Research, located at the Pacific Northwest National Laboratory in Richland, WA, USA. The work conducted by the U.S. Department of Energy Joint Genome Institute (JGI), was supported by the Office of Science of the U.S. Department of Energy under Contract No. DE‐AC02‐05CH11231. CSL was supported by the CatchBio program. White‐rot fungi, such as Dichomitus squalens, degrade all wood components and inhabit mixed‐wood forests containing both soft‐ and hardwood species. In this study, we evaluated how D. squalens responded to the compositional differences in softwood [guaiacyl (G) lignin and higher mannan content] and hardwood [syringyl/guaiacyl (S/G) lignin and higher xylan content] using semi‐natural solid cultures. Spruce (softwood) and birch (hardwood) sticks were degraded by D. squalens as measured by oxidation of the lignins using 2D‐NMR. The fungal response as measured by transcriptomics, proteomics and enzyme activities showed a partial tailoring to wood composition. Mannanolytic transcripts and proteins were more abundant in spruce cultures, while a proportionally higher xylanolytic activity was detected in birch cultures. Both wood types induced manganese peroxidases to a much higher level than laccases, but higher transcript and protein levels of the manganese peroxidases were observed on the G‐lignin rich spruce. Overall, the molecular responses demonstrated a stronger adaptation to the spruce rather than birch composition, possibly because D. squalens is mainly found degrading softwoods in nature, which supports the ability of the solid wood cultures to reflect the natural environment. Publisher PDF

The Front Cover shows an attenuated Total Reflection Infrared spectroscopy (ATR-IR) probe monitoring a chemical reaction in the liquid phase, particularly water, at demanding conditions. The light penetrates few microns deep in proximity of the ATR-IR probe and thus any IR-active entity in that range is probed. This research systematically addresses the challenges associated with acquiring operando ATR-IR spectra for liquid/aqueous phase reactions, which is essential for better understanding of chemical reactions in the liquid phase. More information can be found in the Full Paper by Khaled N. M. Khalili et al.

The authors would like to thank the EPSRC (Global Engagement grant EP/K00445X/1 and critical mass grant EP/J018139/1) and the European Union (Marie Curie ITN ‘SuBiCat’ PITN-GA-2013-607044) for financial support. NMSF-Swansea and Mr. Stephen Boyer are kindly acknowledged for mass spectrometry and elemental analysis, respectively. Bite angle and electronic effects on the ruthenium-diphosphine catalysed ether bond cleavage of the lignin β-O-4 model compound 2-phenoxy-1-phenethanol were tested. Enhanced conversion of the substrate was observed with increasing σ-donor capacity of the ligands. Kinetic and thermodynamic data suggest oxidative addition of the dehydrogenated model compound to the diphosphine Ru(0) complex to be rate-limiting. Postprint

A novel route for the production of the versatile chemical building block phthalide from biorenewable furfuryl alcohol and acrylate esters is presented. Two challenges that limit sustainable aromatics production via Diels–Alder (DA) aromatisation—an unfavourable equilibrium position and undesired regioselectivity when using asymmetric addends—were addressed using a dynamic kinetic trapping strategy. Activated acrylates were used to speed up the forward and reverse DA reactions, allowing for one of the four DA adducts to undergo a selective intramolecular lactonisation reaction in the presence of a weak base. The adduct is removed from the equilibrium pool, pulling the system completely to the product with a fixed, desired regiochemistry. A single 1,2‐regioisomeric lactone product was formed in up to 86 % yield and the acrylate activating agent liberated for reuse. The lactone was aromatised to give phthalide in almost quantitative yield in the presence of Ac2O and a catalytic amount of strong acid, or in 79 % using only catalytic acid., An intramolecular trapping strategy allows inherent problems in the Diels–Alder reaction of biomass‐derived furfuryl alcohol, such as regioselectivity and unfavourable equilibrium yields, to be overcome on the way to biomass‐derived aromatics. This strategy provides a high yielding, redox and atom economical approach to produce the versatile phthalide synthon.

Tandem catalysis combines multiple conversion steps, catalysts, and reagents in one reaction medium, offering the potential to reduce waste and time. In this study, Pickering emulsions-emulsions stabilized by solid particles-are used as easy-to-prepare and bioinspired, compartmentalized reaction media for tandem catalysis. Making use of simple and inexpensive acid and base catalysts, the strategy of compartmentalization of two noncompatible catalysts in both phases of the emulsion is demonstrated by using the deacetalization-Knoevenagel condensation reaction of benzaldehyde dimethyl acetal as a probe reaction. In contrast to simple biphasic systems, which do not allow for tandem catalysis and show instantaneous quenching of the acid and base catalysts, the Pickering emulsions show efficient antagonistic tandem catalysis and give the desired product in high yield, as a result of an increased interfacial area and suppressed mutual destruction of the acid and base catalysts.

Diglycerol dicarbonate, which has been highlighted as a potential monomer for the production of non-isocyanate polyurethanes, has been synthesised using as-synthesised hydrotalcites of varying magnesium-to-aluminium ratio as catalyst materials. The hydrotalcite materials were aged for two different times, influencing their crystallite size. The catalytic carbonylation of diglycerol into diglycerol dicarbonate with dimethyl carbonate as “CO” source and solvent, ran to full conversion within 6 h, with complete selectivity, operating at relatively mild temperatures. Diglycerol monocarbonate was observed as a reaction intermediate in this conversion process. The increased basicity observed with increasing Mg/Al ratio led to higher activities. The catalysts can be easily recovered and re-used without any further activation treatment, whilst still displaying their high activity.

Protonated ferrierite shows superior activity and selectivity in the liquid-phase isomerisation of linear unsaturated fatty acids to (mono-)branched-chain unsaturated fatty acids, (Mo)BUFA. This high selectivity is remarkable, as most of the interior surface of the zeolite is blocked already at the onset of reaction, limiting reaction to the pore mouth. A detailed study of the relationship between ferrierite acidity and performance is reported for five commercial catalysts; significant differences were found, independently of their bulk Si/AI ratios. Initial pore conversion correlates with Bronsted acidity in the 10-MR channels, as determined by adsorption/desorption of pyridine and FTIR. A low density of external acid sites reduces oligomerisation of fatty acids, while a high ratio of Bronsted to Lewis sites explains the observed high BUFA yield. The combination of FTIR with CO adsorption, and temperature-programmed desorption of NH3, confirms that the presence of strong but few Bronsted acid sites in the 10-MR channels increases selectivity to MoBUFA. (C) 2015 Elsevier Inc. All rights reserved.

The valorization of the humin byproducts that are formed during hydrothermal, acid-catalyzed dehydration of carbohydrates is hampered by the insolubility of these byproducts. Here, we report on an alkaline pretreatment method that allows for the insolubility of this highly recalcitrant and structurally complex feed to be overcome. The reactive solubilization of glucose-derived humins was found to require a treatment at 200 degrees C in 0.5 M NaOH for 3.5 h. Fructose- and xylose-derived humins were found to be more recalcitrant, and complete dissolution required raising the temperature to 240 degrees C. Gel permeation chromatographic analyses show the relative average molecular weight of the now soluble humins to decrease with increasing temperature and reaction time. The alkali-treated humins are soluble in water of pH >= 7. Elemental analysis, IR, 2D PASS C-13 solid-state NMR and pyrolysis-GC MS (gas chromatography mass spectrometry) data indicate that the alkaline pretreatment leads to considerable changes in the molecular structure of the humins. Cleavage of C-O-C bonds and further aromatization of the originally highly furanic humins result in the formation of (polycyclic) aromatic structures decorated with carboxylic acids. The combination of the reduction in Mw and the formation of polar functional groups are thought to be the reasons behind the improved solubility.

Humin by-products are formed during the acid-catalyzed dehydration of carbohydrates to bio-based platform molecules, such as hydroxymethylfurfural and levulinic acid. The molecular structure of these humins has not yet been unequivocally established. 1D 13C solid-state NMR data reported have, for example, provided considerable insight, but do not allow for the unambiguous assignment of key structural motifs. Complementary (2D) techniques are needed to gain additional insight into the molecular structure of humins. Here, the preparation of 13C-enriched humins is reported, together with the reactive solubilization of these labeled humins and their characterization with complementary 1D and 2D solid-state NMR techniques. 1D cross polarization (CP) and direct excitation (DE) 13C solid-state NMR spectra, 2D 13C-detected double-quantum single-quantum (DQSQ) as well as 2D 1H-detected heteronuclear correlation (HETCOR) were recorded with different excitation schemes. These experiments unambiguously established that the original humins have a furan-rich structure with aliphatic linkers and allowed for a refinement of the molecular structure proposed previously. Solid-state NMR data of alkali-treated 13C-labeled humins showed that an arene-rich structure is formed at the expense of the furanic network during alkaline pretreatment.

The Lebedev ethanol-to-butadiene process entails a complex chain of reactions that require catalysts to possess a subtle balance in the number and strength of acidic and basic sites. SiO2-MgO materials can be excellent Lebedev catalysts if properly prepared, as catalyst performance has been found to depend significantly on the synthesis method. To assess the specific requirements for butadiene production in terms of active sites and to link their presence to the specific preparation method applied, five distinct SiO2-MgO catalysts, prepared by wet-kneading and co-precipitation methods, were thoroughly characterized. The amount and strength of the acidic (pyridine-IR and NH3-TPD) and basic (CDCl3-IR and CO2-TPD) sites of the materials as well as the overall acid/base properties in the liquid phase (Hammett indicators) were determined. The number of acidic and strong basic sites could be correlated with the extent of ethylene and diethyl ether by-product formation. The best performing catalysts are those containing a small amount of strong basic sites, combined with an intermediate amount of acidic sites and weak basic ones. These results thus provide further insight into the relation between the amount and strength of acidic/basic sites, preparation method and catalytic performance.

The presence of biogenic or process‐derived impurities poses a major problem on the efficient catalytic hydrogenation of biomass‐derived levulinic acid to γ‐valerolactone; hence, studies on their influence on catalyst stability are now required. Herein, the influence of sulfuric acid as feed impurity on the performance of Ru‐based heterogeneous catalysts, including Ru/ZrO2 and mono‐ and bimetallic Ru‐on‐carbon catalysts in dioxane as solvent, was investigated. The carbon‐supported Ru catalysts proved to be very sensitive to minor amounts of sulfuric acid. In stark contrast, Ru/ZrO2 showed a remarkable stability in the presence of the same impurity, which is attributed to the sulfate‐ion adsorption capacity of the support. Preferential sulfate adsorption onto the surface of ZrO2 effectively protects the Ru active phase from deactivation by sulfur poisoning. A simple catalyst regeneration strategy was effective in removing adsorbed impurities, allowing efficient catalyst recycling.

The formation and nature of coke (precursor) species has been studied during the skeletal isomerisation of oleic acid catalysed by protonated ferrierite, in the presence and absence of a triphenylphosphine promoter. UV-Vis and FT-IR spectroscopic analyses of the spent catalyst materials, complemented by NMR and mass spectrometry of the coke deposits extracted after HF dissolution, provide new insights into the deactivation mechanisms. Initial high catalyst activity and selectivity are quickly lost, despite conservation of the framework integrity, as a result of severe deactivation. Pore blockage is detected very early in the reaction, and only the pore mouth is actively employed. Additionally, polyenylic carbocations formed by hydrogen transfer reactions poison the active sites; they are considered to be the precursors to traces of condensed aromatics detected in the spent catalyst. Dodecyl benzene is the major "coke" constituent, and its precursor probably also competes for the active sites. (C) 2014 Elsevier Inc. All rights reserved.

Bio‐based furanics can be aromatized efficiently by sequential Diels–Alder (DA) addition and hydrogenation steps followed by tandem catalytic aromatization. With a combination of zeolite H‐Y and Pd/C, the hydrogenated DA adduct of 2‐methylfuran and maleic anhydride can thus be aromatized in the liquid phase and, to a certain extent, decarboxylated to give high yields of the aromatic products 3‐methylphthalic anhydride and o‐ and m‐toluic acid. Here, it is shown that a variation in the acidity and textural properties of the solid acid as well as bifunctionality offers a handle on selectivity toward aromatic products. The zeolite component was found to dominate selectivity. Indeed, a linear correlation is found between 3‐methylphthalic anhydride yield and the product of (strong acid/total acidity) and mesopore volume of H‐Y, highlighting the need for balanced catalyst acidity and porosity. The efficient coupling of the dehydration and dehydrogenation steps by varying the zeolite‐to‐Pd/C ratio allowed the competitive decarboxylation reaction to be effectively suppressed, which led to an improved 3‐methylphthalic anhydride/total aromatics selectivity ratio of 80 % (89 % total aromatics yield). The incorporation of Pd nanoparticles in close proximity to the acid sites in bifunctional Pd/H‐Y catalysts also afforded a flexible means to control aromatic products selectivity, as further demonstrated in the aromatization of hydrogenated DA adducts from other diene/dienophile combinations.

© 2016 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.Lignin is an abundant biopolymer with a high carbon content and high aromaticity. Despite its potential as a raw material for the fuel and chemical industries, lignin remains the most poorly utilised of the lignocellulosic biopolymers. Effective valorisation of lignin requires careful fine-tuning of multiple “upstream” (i.e., lignin bioengineering, lignin isolation and “early-stage catalytic conversion of lignin”) and “downstream” (i.e., lignin depolymerisation and upgrading) process stages, demanding input and understanding from a broad array of scientific disciplines. This review provides a “beginning-to-end” analysis of the recent advances reported in lignin valorisation. Particular emphasis is placed on the improved understanding of lignins biosynthesis and structure, differences in structure and chemical bonding between native and technical lignins, emerging catalytic valorisation strategies, and the relationships between lignin structure and catalyst performance.

Large zeolite crystals of ferrierite have been used to study the deactivation, at the single particle level, of the alkyl isomerisation catalysis of oleic acid and elaidic acid by a combination of visible micro-spectroscopy and fluorescence microscopy (both polarised wide-field and confocal modes). The large crystals did show the desired activity, albeit only traces of the isomerisation product were obtained and low conversions were achieved compared to commercial ferrierite powders. This limited activity is in line with their lower external non-basal surface area, supporting the hypothesis of pore mouth catalysis. Further evidence for the latter comes from visible micro-spectroscopy, which shows that the accumulation of aromatic species is limited to the crystal edges, while fluorescence microscopy strongly suggests the presence of polyenylic carbocations. Light polarisation associated with the spatial resolution of fluorescence microscopy reveals that these carbonaceous deposits are aligned only in the larger 10-MR channels of ferrierite at all crystal edges. The reaction is hence further limited to these specific pore mouths.

Renewable aromatics can be conveniently synthesized from furanics by introducing an intermediate hydrogenation step in the Diels–Alder (DA) aromatization route, to effectively block retro‐DA activity. Aromatization of the hydrogenated DA adducts requires tandem catalysis, using a metal‐based dehydrogenation catalyst and solid acid dehydration catalyst in toluene. Herein it is demonstrated that the hydrogenated DA adducts can instead be conveniently converted into renewable aromatics with up to 80 % selectivity in a solid‐phase reaction with shorter reaction times using only an acidic zeolite, that is, without solvent or dehydrogenation catalyst. Hydrogenated adducts from diene/dienophile combinations of (methylated) furans with maleic anhydride are efficiently converted into renewable aromatics with this new route. The zeolite H‐Y was found to perform the best and can be easily reused after calcination.

Glycerol is an attractive renewable building block for the synthesis of polyglycerols, which find application in the cosmetic and pharmaceutical industries. The selective etherification of glycerol to higher oligomers was studied in the presence of CaO colloids and the data are compared with those obtained from NaOH and CaO. The materials were prepared by dispersing CaO, CaCO3, or Ca(OH)2 onto a carbon nanofiber (CNF) support. Colloidal nanoparticles were subsequently dispensed from the CNF into the reaction mixture to give CaO colloids that have a higher activity than equimolar amounts of bulk CaO and NaOH. Optimization of the reaction conditions allowed us to obtain a product with Gardner color number

The catalytic hydrogenation of levulinic acid, a key platform molecule in many biorefinery schemes, into γ-valerolactone is considered as one of the pivotal reactions to convert lignocellulose-based biomass into renewable fuels and chemicals. Here we report on the development of highly active, selective and stable supported metal catalysts for this reaction and on the beneficial effects of metal nano-alloying. Bimetallic random alloys of gold-palladium and ruthenium-palladium supported on titanium dioxide are prepared with a modified metal impregnation method. Gold-palladium/titanium dioxide shows a marked,~27-fold increase in activity (that is, turnover frequency of 0.1 s−1) compared with its monometallic counterparts. Although ruthenium-palladium/titanium dioxide is not only exceptionally active (that is, turnover frequency of 0.6 s−1), it shows excellent, sustained selectivity to γ-valerolactone (99%). The dilution and isolation of ruthenium by palladium is thought to be responsible for this superior catalytic performance. Alloying, furthermore, greatly improves the stability of both supported nano-alloy catalysts., The hydrogenation of leuvinic acid to γ-valerolactone is an important step in the conversion of lignocellulose to high value chemicals. Here, the authors report that bimetallic alloys are active and stable catalysts for this reaction, and attribute this to geometric and electronic effects.

A novel route for the production of renewable aromatic chemicals, particularly substituted phthalic acid anhydrides, is presented. The classical two-step approach to furanics-derived aromatics via Diels-Alder (DA) aromatization has been modified into a three-step procedure to address the general issue of the reversible nature of the intermediate DA addition step. The new sequence involves DA addition, followed by a mild hydrogenation step to obtain a stable oxanorbornane intermediate in high yield and purity. Subsequent one-pot, liquid-phase dehydration and dehydrogenation of the hydrogenated adduct using a physical mixture of acidic zeolites or resins in combination with metal on a carbon support then allows aromatization with yields as high as 84 % of total aromatics under relatively mild conditions. The mechanism of the final aromatization reaction step unexpectedly involves a lactone as primary intermediate.

Catechol intradiol dioxygenation is a unique reaction catalyzed by iron-dependent enzymes and non-heme iron(III) complexes. The mechanism by which these systems activate dioxygen in this important metabolic process remains controversial. Using a combination of kinetic measurements and computational modelling of multiple iron(III) catecholato complexes, we have elucidated the catechol cleavage mechanism and show that oxygen binds the iron center by partial dissociation of the substrate from the iron complex. The iron(III) superoxide complex that is formed subsequently attacks the carbon atom of the substrate by a rate-determining C[BOND]O bond formation step.

The first Fe-based catalytic system for the oxidative cleavage of unsaturated fatty acids and esters to carboxylic acids is reported. The system comprises [Fe(OTf)(2)(6-Me-PyTACN)] (2) (6-Me-PyTACN = 1-[(6-methyl-2-pyridyl) methyl]-4,7-dimethyl-1,4,7-triazacyclononane, OTf = trifluoromethane sulfonate anion) as the catalyst (3 mol%) either with a combination of hydrogen peroxide and NaIO4 or exclusively with NaIO4 as the oxidant, and operates at 0 degrees C or ambient temperature. Under these standard conditions (method A), methyl oleate is converted in a one-pot procedure into 50-55% of both nonanoic and azelaic acid, together with some epoxide and aldehyde intermediates as byproducts. These yields can be further improved by addition of sulfuric acid (method B) to hydrolyze the epoxide byproducts, by including a pH neutralization step and addition of more catalyst (1 mol%). Under the optimized conditions, both methyl oleate and oleic acid are converted into high yields of the corresponding carboxylic acids (80-85%). Overall, this catalytic system provides an alternative to the industrial ozonolysis of oleic acid and to catalytic Ru-and Os-based systems for the oxidative cleavage of unsaturated fatty acids and ester B.M.W. and R.J.M.K.G. acknowledge Utrecht University for financial support through its 'Focus and Massa' program. M.C. acknowledges financial support from the European Research Council (ERC-2009-StG-239910), MINECO of Spain (CTQ2012-37420-C02-01/BQU, Consolider-Ingenio CSD2010-00065) and the Catalan DIUE of the Generalitat de Catalunya (2009SGR637 and ICREA Academia Award). The X-ray diffractometer has been financed by the Netherlands Organization for Scientific Research (NWO)

Lignin and humins are both (by-)products of biorefining processes aimed at the valorization of lignocellulosic biomass. In order to improve the efficiency of such biorefineries and to develop new valorization pathways for these polymeric materials, detailed insight into their complex chemical structure and functional group distribution is required. Here, we report on the quantification and classification of the ketone and aldehyde carbonyl functional groups contained in these two polymers by 19F NMR. The known method of carbonyl derivatization with 4-(trifluoromethyl)phenylhydrazine to the corresponding hydrazone has been improved and simplified, allowing derivatization directly in an NMR tube, requiring no additional workup before quantification by 19F NMR. Furthermore, the scope of the method was assessed and expanded, with model compound studies, which included monomeric and dimeric compounds as well as synthetic polymers, showing that the carbonyl functions can indeed be reproducibly quantified. Using this model compound library, the carbonyl functional groups in two technical lignins (Indulin Kraft and Alcell) and, for the first time, an industrial humin could be quantified and classified. The industrial humin was found to contain 6.6 wt % of carbonyl functions, with aliphatic and conjugated carbonyls being detected. The relatively high abundance of such functional groups, which are amenable to further chemical modification, provides opportunities for the use of these humin byproducts in various applications, e.g., as materials after derivatization.

P.C.A.B. thanks the Netherlands Organization for Scientific Research (NWO) for a Vernieuwingsimpuls Veni Grant. The CatchBio program is acknowledged for financial support. N.J.W. thanks EPSRC for funding by the EP/J018139/1, EP/K00445X/1 grants and an EPSRC Doctoral Prize Fellowship to C.S.L. Saumya Dabral and Prof. Carsten Bolm (RWTH Aachen) are gratefully acknowledged for providing an authentic sample of 5b. Dr. Wouter Huijgen (ECN) is acknowledged for Klason lignin determination. SuBiCat Initial Training Network, Call FP7-PEOPLE-2013-ITN, #607044) is gratefully acknowledged. Lignin is an attractive renewable feedstock for aromatic bulk and fine chemicals production, provided that suitable depolymerization procedures are developed. Here, we describe a tandem catalysis strategy for ether linkage cleavage within lignin, involving ether hydrolysis by water-tolerant Lewis acids followed by aldehyde decarbonylation by a rhodium complex. In situ decarbonylation of the reactive aldehydes limits loss of monomers by recondensation, a major issue in acid-catalyzed lignin depolymerization. Rate of hydrolysis and decarbonylation were matched using lignin model compounds, allowing the method to be successfully applied to softwood, hardwood and herbaceous dioxasolv lignins as well as poplar sawdust to give the anticipated decarbonylation products, and, rather surprisingly, 4-(1-propenyl)phenols. Promisingly, product selectivity can be tuned by variation of Lewis acid strength and lignin source. Publisher PDF

Wet-kneading is a technique commonly used for the synthesis of SiO2–MgO catalysts for the Lebedev ethanol-to-butadiene process, with catalyst performance known to depend heavily on the preparation parameters used in this method. Here, the large influence of Mg precursor and MgO content on morphology, chemical structure (as determined by TEM(-EDX), FT-IR, XRD and solid-state 1H–29Si cross-polarized MAS NMR), and on catalyst performance is demonstrated. The Mg precursor used is found to influence the extent of magnesium silicate formation during wet-kneading, as estimated from TEM and FT-IR, which, in turn, was found to correlate with catalyst performance. Accordingly, the catalyst synthesized from a nanosized Mg(OH)2 precursor (SiO2–MgO (III)nano), showing the highest degree of chemical contact between the SiO2 and MgO components, gave the highest butadiene yield. Variation of the Mg/Si ratio in a series of SiO2–MgO (III)nano materials showed a volcano-type dependence of the butadiene yield on MgO content. 1H–29Si CP-MAS NMR studies allowed for the identification of the type and an estimation of the amount of magnesium silicates formed during wet-kneading. Here, we argue that the structural characteristics of the hydrous magnesium silicates, lizardite and talc, formed during catalyst preparation, together with the ratio of the magnesium silicates to MgO, determine the overall acid/base properties of the SiO2–MgO (III)nano catalyst materials and as a result, catalyst performance.

Detailed insight into the structure and composition of industrial (technical) lignins is needed to devise efficient thermal, bio- or chemocatalytic valorisation strategies. Six such technical lignins covering three main industrial pulping methods (Indulin AT Kraft, Protobind 1000 soda lignin and Alcell, poplar, spruce and wheat straw organosolv lignins) were comprehensively characterised by lignin composition analysis, FT-IR, pyrolysis-GC-MS, quantitative 31P and 2D HSQC NMR analysis and molar mass distribution by Size Exclusion Chromatography (SEC). A comparison of nine SEC methods, including the first analysis of lignins with commercial alkaline SEC columns, showed molar masses to vary considerably, allowing some recommendations to be made. The lignin molar mass decreased in the order: Indulin Kraft > soda P1000 > Alcell > OS-W ∼ OS-P ∼ OS-S, regardless of the SEC method chosen. Structural identification and quantification of aromatic units and inter-unit linkages indicated that all technical lignins, including the organosolv ones, have considerably been degraded and condensed by the pulping process. Importantly, low amounts of β- ether linkages were found compared to literature values for protolignin and lignins obtained by other, milder isolation processes. Stilbenes and ether furfural units could also be identified in some of the lignins. Taken together, the insights gained in the structure of the technical lignins, in particular, the low β-O-4 contents, carry implications for the design of lignin valorisation strategies including (catalytic) depolymerisation and material applications.

(Multifunctional) cyclic carbonates are generating much interest, with bio-based bis-cyclic compounds attracting attention from the polymer sector as potential renewable monomers for systems such as non-isocyanate polyurethanes. Here, the efficient synthesis of one such substrate, diglycerol dicarbonate, utilising CO2-masked N-heterocyclic carbene (NHC) organocatalysts is demonstrated. The 1,3-dialkylimidazole-2-carboxylate pre-catalyst, which can be produced both in and ex situ, yields the desired cyclic product, expressing full conversion within 3 h when using the ex situ synthesised pre-catalyst with 5 mol% loading, but can also operate with 1 mol% loading efficiently. Substituted derivatives of the imidazole-based organocatalyst have also been investigated to gauge the sensitivity of the system. A number of bio-based diols are also investigated, with 1,2-, 2,3- and 1,3-diols yielding five- and six-membered cyclic products, respectively; 1,3-diols are significantly more reluctant to cyclisation, yielding both 1- and 3-monocarbonates, dicarbonates and the cyclic products. A more in depth study was also carried out on glycerol as a substrate, both in its pure a crude form, providing insight into how impurities impact on the activity of the carbene catalyst. Through 13C-labelled reagent experiments, a mechanism is proposed for the conversion of diols to their cyclic carbonate analogues. Finally, the organocatalyst was immobilized on siliceous mesostructured cellular foam (MCF). Using an alternative activation procedure, a supported, masked NHC catalyst is achieved and characterised with DRIFTS, TGA and 13C solid-state NMR. This heterogenised catalyst can be easily recovered and reused up to three times expressing its original activity if properly regenerated by a simple ion exchange procedure. Of important note, this system can also successfully convert crude glycerol with high selectivity observed for the cyclic product.

Proteins sharing the same 2-His-1-carboxylate structural motif have little amino acid sequence similarity and are able to perform many different reactions. Many factors have been cited to explain their different specificity and turnover rates, like protein environment, coordinated ligand geometry, electronic structure of the active site, etc. In this paper, we present a combined approach applying high-resolution XANES spectroscopy and theory simulations to different model complexes that mimic the binding modes of the amino acids to the metal site. Experiments were performed on three compounds showing three metal sites: ferrous hexacoordinate, ferric pentacoordinate and ferrous pentacoordinate. The first two compounds bear an N,N,O-tridentate 3,3-bis(1-alkylimidazol-2-yl)propionate ligand that features a monodentate carboxylate group. These complexes mimic the activity of extradiol dioxygenases but also exhibit intradiol cleavage activity. The third compound features a bidentate terphenylcarboxylate ligand and a sterically hindered bidentate N,N-donor, thus providing a good structural mimic of the ternary enzyme-tetrahydrobiopterin-substrate complex in pterin-dependent phenylalanine hydroxylase, which also contains a bidentate carboxylate. Modeling of high-resolution XANES on well-defined model complexes of different geometry can aid in protein structure elucidation. XANES gives the oxidation state and coordination number of the metal in the non-crystallized protein at natural pH. The accuracy of the results is limited by the core-hole and experimental broadenings. We found that high-resolution XANES experiments give increased resolution at the pre-edges, but limited improvement at the main edge. These high-resolution pre-edges can be accurately simulated by using crystal field multiplet theory (CFM). We show that by combining modelling and XANES simulations with FEFF8, detailed structural and chemical information can be obtained. We found that a short O2metal distance for the carboxylate oxygen atom not bound to the metal causes a higher white line in FeII, which is similar to the results obtained for the pterin-dependent hydroxylase, tyrosine hydroxylase (TYH). Full-potential FDMNES simulations for each sample confirm the accuracy of the main results with muffin-tin approximation (FEFF8).