Benzenoid Aromatics from Renewable Resources.

In this Review, all known chemical methods for the conversion of renewable resources into benzenoid aromatics are summarized. The raw materials that were taken into consideration are CO2; lignocellulose and its constituents cellulose, hemicellulose, and lignin; carbohydrates, mostly glucose, fructose, and xylose; chitin; fats and oils; terpenes; and materials that are easily obtained via fermentation, such as biogas, bioethanol, acetone, and many more. There are roughly two directions. One much used method is catalytic fast pyrolysis carried out at high temperatures (between 300 and 700 °C depending on the raw material), which leads to the formation of biochar; gases, such as CO, CO2, H2, and CH4; and an oil which is a mixture of hydrocarbons, mostly aromatics. The carbon selectivities of this method can be reasonably high when defined small molecules such as methanol or hexane are used but are rather low when highly oxygenated compounds such as lignocellulose are used. The other direction is largely based on the multistep conversion of platform chemicals obtained from lignocellulose, cellulose, or sugars and a limited number of fats and terpenes. Much research has focused on furan compounds such as furfural, 5-hydroxymethylfurfural, and 5-chloromethylfurfural. The conversion of lignocellulose to xylene via 5-chloromethylfurfural and dimethylfuran has led to the construction of two large-scale plants, one of which has been operational since 2023.

Nylon Intermediates from Bio-Based Levulinic Acid.

Use of ZrO2 /SiO2 as a solid acid catalyst in the ring-opening of biobased γ-valerolactone with methanol in the gas phase leads to mixtures of methyl 2-, 3-, and 4-pentenoate (MP) in over 95 % selectivity, containing a surprising 81 % of M4P. This process allows the application of a selective hydroformylation to this mixture to convert M4P into methyl 5-formyl-valerate (M5FV) with 90 % selectivity. The other isomers remain unreacted. Reductive amination of M5FV and ring-closure to ϵ-caprolactam in excellent yield had been reported before. The remaining mixture of 2- and 3-MP was subjected to an isomerising methoxycarbonylation to dimethyl adipate in 91 % yield.

A simple guiding principle for the temperature dependence of the solubility of light gases in imidazolium-based ionic liquids derived from molecular simulations.

We have determined the temperature dependence of the solvation behavior of a large collection of important light gases in imidazolium-based ionic liquids with the help of extensive molecular dynamics simulations. The motivation of our study is to unravel common features of the temperature dependent solvation under well controlled conditions, and to provide a guidance for cases, where experimental data from different sources disagree significantly. The solubility of molecular hydrogen, oxygen, nitrogen, methane, krypton, argon, neon and carbon dioxide in the imidazolium based ionic liquids of type 1-n-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Cnmim][NTf2]) with varying alkyl side chain lengths n = 2, 4, 6, 8 is computed for a temperature range between 300 K and 500 K at 1 bar. By applying Widom's particle insertion technique and Bennet's overlapping distribution method, we are able to determine the temperature dependent solvation free energies of those selected light gases in simulated imidazolium based ionic liquids with high statistical accuracy. Our simulations demonstrate that the magnitude of the solvation free energy of a gas molecule at a chosen reference temperature and that of its temperature-derivatives are intimately related to one another. We conclude that this "universal" behavior is rooted in a solvation entropy-enthalpy compensation effect, which seems to be a defining feature of the solvation of small molecules in ionic liquids. The observations lead to simple analytical relations, determining the temperature dependence of the solubility data based on the absolute solubility at a certain reference temperature. By comparing our results with available experimental data from many sources, we can show that our approach is particularly helpful for providing reliable estimates for the solvation behavior of very light gases, such as hydrogen, where conflicting experimental data exist.

Mechanical complexity of living cells can be mapped onto simple homogeneous equivalents.

Biological cells are built up from different constituents of varying size and stiffness which all contribute to the cell's mechanical properties. Despite this heterogeneity, in the analysis of experimental measurements one often assumes a strongly simplified homogeneous cell and thus a single elastic modulus is assigned to the entire cell. This ad-hoc simplification has so far mostly been used without proper justification. Here, we use computer simulations to show that indeed a mechanically heterogeneous cell can effectively be replaced by a homogeneous equivalent cell with a volume averaged elastic modulus. To demonstrate the validity of this approach, we investigate a hyperelastic cell with a heterogeneous interior under compression and in shear/channel flow mimicking atomic force and microfluidic measurements, respectively. We find that the homogeneous equivalent cell reproduces quantitatively the behavior of its heterogeneous counterpart, and that this equality is largely independent of the stiffness or spatial distribution of the heterogeneity.

Cobalt nanoparticle-catalysed N-alkylation of amides with alcohols.

A protocol for efficient N-alkylation of benzamides with alcohols in the presence of cobalt-nanocatalysts is described. Key to the success of this general methodology is the use of highly dispersed cobalt nanoparticles supported on carbon, which are obtained from the pyrolysis of cobalt(ii) acetate and o-phenylenediamine as a ligand at suitable temperatures. The catalytic material shows a broad substrate scope and good tolerance to functional groups. Apart from the synthesis of a variety of secondary amides (>45 products), the catalyst allows for the conversion of more challenging aliphatic alcohols and amides, including biobased and macromolecular amides. The practical applicability of the catalyst is underlined by the successful recycling and reusability.

Heterogenized Molecular Electrocatalyst Based on a Hydroxo-Bridged Binuclear Copper(II) Phenanthroline Compound for Selective Reduction of CO2 to Ethylene.

Molecular copper catalysts have emerged as promising candidates for the electrochemical reduction of CO2 . Notable features of such systems include the ability of Cu to generate C2+  products and the well-defined active sites that allow for targeted structural tuning. However, the frequently observed in situ formation of Cu nanoclusters has undermined the advantages of the molecular frameworks. It is therefore desirable to develop Cu-based catalysts that retain their molecular structures during electrolysis. In this context, a heterogenized binuclear hydroxo-bridged phenanthroline Cu(II) compound with a short Cu···Cu distance is reported as a simple yet efficient catalyst for electrogeneration of ethylene and other C2 products. In an aqueous electrolyte, the catalyst demonstrates remarkable performance, with excellent Faradaic efficiency for C2 products (62%) and minimal H2 evolution (8%). Furthermore, it exhibits high stability, manifested by no observable degradation during 15 h of continuous electrolysis. The preservation of the atomic distribution of the active sites throughout electrolysis is substantiated through comprehensive characterizations, including X-ray photoelectron and absorption spectroscopy, scanning and transmission electron microscopy, UV-vis spectroscopy, as well as control experiments. These findings establish a solid foundation for further investigations into targeted structural tuning, opening new avenues for enhancing the catalytic performance of Cu-based molecular electrocatalysts.

Correction: Time-, space- and energy-resolved in situ characterization of catalysts by X-ray absorption spectroscopy.

Correction for 'Time-, space- and energy-resolved in situ characterization of catalysts by X-ray absorption spectroscopy' by Stefan Peters et al., Chem. Commun., 2023, 59, 12120-12123, https://doi.org/10.1039/D3CC03277A.

An improved preparation method for a CuO/CeO2-coated monolith for the CO-PrOx reaction.

In this study, we present a method for directly coating monoliths with a CeO2/CuO catalyst using the urea-nitrate combustion method. The catalyst was characterized by means of XRD, SEM/EDX, and EPR measurements. Experimental results are described, when this catalyst was used for the preferential oxidation of CO. The catalytic activity for the CO-PrOx-reaction was measured by recording CO conversion as a function of the reaction temperature in a hydrogen-rich gas mixture in the presence and absence of water vapor. In a long-term test of over 310 h, the catalyst's long-term stability was demonstrated. Direct coating is shown to be a promising approach by which a larger amount of catalyst can be deposited onto the monolith in a single step than would be possible with washcoats.

Comparative Study of Commercial Silica and Sol-Gel-Derived Porous Silica from Cornhusk for Low-Temperature Catalytic Methane Combustion.

The synthesis and characterization of sol-gel-derived cornhusk support for low-temperature catalytic methane combustion (LTCMC) were investigated in this study. The prepared cornhusk support was impregnated with palladium and cerium oxide (Pd/CeO2) via the classical incipient wetness method. The resulting catalyst was characterized using various techniques, including X-ray diffraction (XRD), N2 physisorption (BET), transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H2-TPR). The catalytic performance of the Pd/CeO2/CHSiO2 catalyst was evaluated for methane combustion in the temperature range of 150-600 °C using a temperature-controlled catalytic flow reactor, and its performance was compared with a commercial catalyst. The results showed that the Pd/CeO2 dispersed on SiO2 from the cornhusk ash support (Pd/CeO2/CHSiO2) catalyst exhibited excellent catalytic activity for methane combustion, with a conversion of 50% at 394 °C compared with 593 °C for the commercial silica catalyst (Pd/CeO2/commercial). Moreover, the Pd/CeO2/CHSiO2 catalyst displayed better catalytic stability after 10 h on stream, with a 7% marginal loss in catalytic activity compared with 11% recorded for the Pd/CeO2/commercial catalyst. The N2 physisorption and H2-TPR results indicated that the cornhusk SiO2 support possessed a higher surface area and strong reducibility than the synthesized commercial catalyst, contributing to the enhanced catalytic activity of the Pd/CeO2/SiO2 catalyst. Overall, the SiO2 generated from cornhusk ash exhibited promising potential as a low-cost and environmentally friendly support for LTCMC catalysts.

Streamlining the synthesis of amides using Nickel-based nanocatalysts.

The synthesis of amides is a key technology for the preparation of fine and bulk chemicals in industry, as well as the manufacture of a plethora of daily life products. Furthermore, it constitutes a central bond-forming methodology for organic synthesis and provides the basis for the preparation of numerous biomolecules. Here, we present a robust methodology for amide synthesis compared to traditional amidation reactions: the reductive amidation of esters with nitro compounds under additives-free conditions. In the presence of a specific heterogeneous nickel-based catalyst a wide range of amides bearing different functional groups can be selectively prepared in a more step-economy way compared to previous syntheses. The potential value of this protocol is highlighted by the synthesis of drugs, as well as late-stage modifications of bioactive compounds. Based on control experiments, material characterizations, and DFT computations, we suggest metallic nickel and low-valent Ti-species to be crucial factors that makes this direct amide synthesis possible.

Time-, space- and energy-resolved in situ characterization of catalysts by X-ray absorption spectroscopy.

A setup for dispersive X-ray absorption spectroscopy (XAS) with spatial, temporal and energy resolution is presented. Through investigation of a Mo/HZSM-5 catalyst during the dehydroaromatization of methane we observed a reduction gradient along the packed bed. Our new method represents an unprecedented addition to the analytical toolbox for in situ characterizations.

Structural Evolution of Iron-Loaded Metal-Organic Framework Catalysts for Continuous Gas-Phase Oxidation of Methane to Methanol.

Catalytic partial oxidation of methane presents a promising route to convert the abundant but environmentally undesired methane gas to liquid methanol with applications as an energy carrier and a platform chemical. However, an outstanding challenge for this process remains in developing a catalyst that can oxidize methane selectively to methanol with good activity under continuous flow conditions in the gas phase using O2 as an oxidant. Here, we report a Fe catalyst supported by a metal-organic framework (MOF), Fe/UiO-66, for the selective and on-stream partial oxidation of methane to methanol. Kinetic studies indicate the continuous production of methanol at a superior reaction rate of 5.9 × 10-2 µmolMeOH gFe-1 s-1 at 180 °C and high selectivity toward methanol, with the catalytic turnover verified by transient methane isotopic measurements. Through an array of spectroscopic characterizations, electron-deficient Fe species rendered by the MOF support is identified as the probable active site for the reaction.

Water oxidation with molecularly defined iridium complexes: insights into homogeneous versus heterogeneous catalysis.

Molecularly defined Ir complexes and different samples of supported IrO(2) nanoparticles have been tested and compared in the catalytic water oxidation with cerium ammonium nitrate (CAN) as the oxidant. By comparing the activity of nano-scaled supported IrO(2) particles to the one of organometallic complexes it is shown that the overall activity of the homogeneous Ir precursors is defined by both the formation of the homogeneous active species and its conversion to Ir(IV)-oxo nanoparticles. In the first phase of the reaction the activity is dominated by the homogeneous active species. With increasing reaction time, the influence of nano-sized Ir-oxo particles becomes more evident. Notably, the different conversion rates of the homogeneous precursor into the active species as well as the conversion into Ir-oxo nanoparticles and the different particle sizes have a significant influence on the overall activity. In addition to the homogeneous systems, IrO(2)@MCM-41 has also been synthesized, which contains stabilized nanoparticles of between 1 and 3 nm in size. This latter system shows a similar activity to IrCl(3)⋅xH(2)O and complexes 4 and 5. Mechanistic insights were obtained by in situ X-ray absorption spectroscopy and scanning transmission electron microscopy.

Separation of H2O/CO2 Mixtures by MFI Membranes: Experiment and Monte Carlo Study.

The separation of CO2 from gas streams is a central process to close the carbon cycle. Established amine scrubbing methods often require hot water vapour to desorb the previously stored CO2. In this work, the applicability of MFI membranes for H2O/CO2 separation is principally demonstrated by means of realistic adsorption isotherms computed by configurational-biased Monte Carlo (CBMC) simulations, then parameters such as temperatures, pressures and compositions were identified at which inorganic membranes with high selectivity can separate hot water vapour and thus make it available for recycling. Capillary condensation/adsorption by water in the microporous membranes used drastically reduces the transport and thus the CO2 permeance. Thus, separation factors of αH2O/CO2 = 6970 could be achieved at 70 °C and 1.8 bar feed pressure. Furthermore, the membranes were tested for stability against typical amines used in gas scrubbing processes. The preferred MFI membrane showed particularly high stability under application conditions.

Synthesis of Single Atom Based Heterogeneous Platinum Catalysts: High Selectivity and Activity for Hydrosilylation Reactions.

Catalytic hydrosilylation represents a straightforward and atom-efficient methodology for the creation of C-Si bonds. In general, the application of homogeneous platinum complexes prevails in industry and academia. Herein, we describe the first heterogeneous single atom catalysts (SACs), which are conveniently prepared by decorating alumina nanorods with platinum atoms. The resulting stable material efficiently catalyzes hydrosilylation of industrially relevant olefins with high TON (≈105). A variety of substrates is selectively hydrosilylated including compounds with sensitive reducible and other functional groups (N, B, F, Cl). The single atom based catalyst shows significantly higher activity compared to related Pt nanoparticles.

Synthesis of nanostructured bismuth titanate microspheres.

A hydrothermal method was developed for the synthesis of bismuth titanate nanostructured microspheres. The precursor powder was prepared using a diethylene glycol mediated coprecipitation method. The as-synthesized nanostructured microspheres consisting of granular nanoparticles and nano-platelets were obtained through a hydrothermal treatment of the precursor powder in aqueous sodium hydroxide solution. Tailoring of the morphology was achieved by changing the precursor quantity, sodium hydroxide concentration, and reaction time. The formation mechanism of the nanostructured microspheres probably involves aggregation, followed by dissolution and recrystallization. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the phase purities, morphologies, and composition of the products.

Crystal structure of (E)-undec-2-enoic acid.

In the mol-ecule of the title low-melting α,ß-unsaturated carb-oxy-lic acid, C11H20O2, the least-squares mean line through the octyl chain forms an angle of 60.10 (13)° with the normal to plane of the acrylic acid fragment (r.m.s. deviation = 0.008 Å). In the crystal, centrosymmetrically related mol-ecules are linked by pairs of O-H⋯O hydrogen bonds into dimers, forming layers parallel to the (041) plane.

Crystal structure of (E)-pent-2-enoic acid.

The mol-ecule of the title compound, C5H8O2, a low-melting α,ß-unsaturated carb-oxy-lic acid, is essentially planar [maximum displacement = 0.0239 (13) Å]. In the crystal, mol-ecules are linked into centrosymmetric dimers via pairs of O-H⋯O hydrogen bonds.

Crystal structure of (E)-hex-2-enoic acid.

The crystal structure of the title compound, C6H10O2, an α,ß-unsaturated carb-oxy-lic acid, displays carb-oxy-lic acid inversion dimers linked by pairs of O-H⋯O hydrogen bonds. The packing is characterized by layers of acid dimers. All the non-H atoms of the (E)-hex-2-enoic acid mol-ecule lie almost in the same plane (r.m.s. deviation for the non-H atoms = 0.018 Å).

Crystal structure of (E)-dodec-2-enoic acid.

The crystal structure of (E)-dodec-2-enoic acid, C12H22O2, an α,ß-unsaturated carb-oxy-lic acid with a melting point (295 K) near room temperature, is characterized by carb-oxy-lic acid inversion dimers linked by pairs of O-H⋯O hydrogen bonds. The carb-oxy-lic acid group and the following three carbon atoms of the chain of the (E)-dodec-2-enoic acid mol-ecule lie almost in one plane (r.m.s. deviation for the four C atoms and two O atoms = 0.012 Å), whereas the remaining carbon atoms of the hydro-carbon chain adopt a nearly fully staggered conformation [moduli of torsion angles vary from 174.01 (13) to 179.97 (13)°].