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ChemSusChem - published by Wiley
'Chemistry and Sustainability Energy and Materials' is well on its way to become a top interdisciplinary journal for research at the interface of chemistry and sustainability with energy research, materials science, chemical engineering, and biotechnology.
The one-pot conversion of lignocellulosic and algal biomass into a liquid fuel, 2,5-dimethylfuran (DMF), has been achieved by using a multicomponent catalytic system comprising [DMA]+[CH3SO3]? (DMA=N,N-dimethylacetamide), Ru/C, and formic acid. The synthesis of DMF from all substrates was carried out under mild reaction conditions. The reaction progressed via 5-hydroxyemthylfurfural (HMF) in the first step followed by hydrogenation and hydrogenolysis of HMF with the Ru/C catalyst and formic acid as a hydrogen source. This report discloses the effectiveness of the Ru/C catalyst for the first time for DMF synthesis from inexpensive and readily abundant biomass sources, which gives a maximum yield of 32?% DMF in 1?h. A reaction route involving 5-(formyloxymethyl)furfural (FMF) as an intermediate has been elucidated based on the 1H and 13C?NMR spectroscopic data. Another promising biofuel, 5-ethoxymethylfurfural (EMF), was also synthesized with high selectivity from polymeric carbohydrate-rich biomass substrates by using a Brønsted acidic ionic liquid catalyst, that is [DMA]+[CH3SO3]?, by etherification of HMF in ethanol.Biomass breakdown in one pot: The one-pot conversion of lignocellulosic and algal biomass into liquid fuel, 2,5-dimethylfuran, has been achieved by using a multicomponent catalytic system comprising [DMA]+[CH3SO3]? (DMA=N,N-dimethylacetamide), Ru/C, and formic acid. A reaction route has been elucidated based on 1H and 13C?NMR spectroscopic data. Another promising biofuel has also been synthesized by using [DMA]+[CH3SO3]? as catalyst.
A simple and low-cost modification method was developed to improve the power generation performance of inexpensive semicoke electrode in microbial fuel cells (MFCs). After carbonization and activation with water vapor at 800–850?°C, the MFC with the activated coke (modified semicoke) anode produced a maximum power density of 74?W?m?3, 17?W?m?3, and 681?mW?m?2 (normalized to anodic liquid volume, total reactor volume, and projected membrane surface area, respectively), which was 124?% higher than MFCs using a semicoke anode (33?W?m?3, 8?W?m?3, and 304?mW?m?2). When they were used as biocathode materials, activated coke produced a maximum power density of 177?W?m?3, 41?W?m?3, and 1628?mW?m?2 (normalized to cathodic liquid volume, total reactor volume, and projected membrane surface area, respectively), which was 211?% higher than that achieved by MFCs using a semicoke cathode (57?W?m?3, 13?W?m?3, and 524?mW?m?2). A substantial increase was also noted in the conductivity, C/O mass ratio, and specific area for activated coke, which reduced the ohmic resistance, increased biomass density, and promoted electron transfer between bacteria and electrode surface. The activated coke anode also produced a higher Coulombic efficiency and chemical oxygen demand removal rate than the semicoke anode.Combining char with microbes: A novel and simple modification method, carbonization and activation, has been developed to enhance the performance of an inexpensive semicoke electrode to be used in microbial fuel cells. The activated coke (modified semicoke) produces a 124?% and 211?% increase in power density when they were used as anode and biocathode materials, respectively.
Iron will: The iron-catalyzed depolymerization of a range of polyethers is studied. The products of the depolymerization reactions are chloroesters, which can be used as starting materials for new polymers. In the presence of simple iron salts extraordinary catalyst activities and selectivities are feasible at low temperature.
Do you sea water? Water consumption will be a challenge in biorefineries, and the use of non-drinkable sources of water will be preferred. Herein, glucose is converted into 5-hydroxymethylfurfural (HMF) in a chemo-enzymatic one-pot, two-step procedure, involving immobilized glucose isomerase to produce fructose and oxalic acid to dehydrate it to HMF.
Support with pom poms: A hybrid material ([Co4(H2O)2(PW9O34)2]10?/mesoporous carbon nitride) is prepared as an efficient water oxidation catalyst, and shows excellent catalytic activity for water oxidation. Mesoporous carbon nitride as an immobilization matrix improves the catalytic water oxidation activity and structural durability of the assembled nanostructures.
The slow kinetics of the electrochemical oxygen reduction reaction (ORR) is a crucial bottleneck in the development of microbial fuel cells (MFCs). This article firstly gives an overview of the particular constraints imposed on ORR by MFC operating conditions: neutral pH, slow oxygen mass transfer, sensitivity to reactive oxygen species, fouling and biofouling. A review of the literature is then proposed to assess how microbial catalysis could afford suitable solutions. Actually, microbial catalysis of ORR occurs spontaneously on the surface of metallic materials and is an effective motor of microbial corrosion. In this framework, several mechanisms have been proposed, which are reviewed in the second part of the article. The last part describes the efforts made in the domain of MFCs to determine the microbial ecology of electroactive biofilms and define efficient protocols for the formation of microbial oxygen-reducing cathodes. Although no clear mechanism has been established yet, several promising solutions have been recently proposed.Microbes win design price: Microbial catalysis of oxygen reduction, which occurs spontaneously on metallic materials immersed in natural waters, can be an effective motor of corrosion. The fundamental advances achieved in studying aerobic microbial corrosion now offer a helpful basis for designing oxygen-reducing microbial cathodes for microbial fuel cells.
Cathodic limitation in microbial fuel cells (MFCs) is considered an important hurdle towards practical application as a bioenergy technology. The oxygen reduction reaction (ORR) needs to occur in MFCs under significantly different conditions compared to chemical fuel cells, including a neutral pH. The common reason cited for cathodic limitation is the difficulty in providing protons to the catalyst sites. Here, we show that it is not the availability of protons, but the transport of OH? from the catalyst layer to the bulk liquid that largely governs cathodic potential losses. OH? is a product of an ORR mechanism that has not been considered dominant before. The accumulation of OH? at the catalyst sites results in an increase in the local cathode pH, resulting in Nernstian concentration losses. For Pt-based gas-diffusion cathodes, using polarization curves developed in unbuffered and buffered solutions, we quantified this loss to be >0.3?V at a current density of 10?A?m?2. We show that this loss can be partially overcome by replacing the Nafion binder used in the cathode catalyst layer with an anion-conducting binder and by providing additional buffer to the cathode catalyst directly in the form of CO2, which results in enhanced OH? transport. Our results provide a comprehensive analysis of cathodic limitations in MFCs and should allow researchers to develop and select materials for the construction of MFC cathodes and identify operational conditions that will help minimize Nernstian concentration losses due to pH gradients.Do not impede OH?! Nernstian concentration overpotential associated with OH? transport limitations in microbial fuel cells cathodes is quantified and found to be an important factor leading to poor performance. Strategies to minimize these losses and thus achieve higher power densities, such as replacing Nafion binder with an anion-conducting binder, are tested and discussed.
Geobacter spp. can form a biofilm that is more than 20??m thick on an anode surface by utilizing the anode as a terminal respiratory electron acceptor. Just how microbes transport electrons through a thick biofilm and across the biofilm/anode interface, and what determines the upper limit to biofilm thickness and catalytic activity (i.e., current, the rate at which electrons are transferred to the anode), are fundamental questions attracting substantial attention. A significant body of experimental evidence suggests that electrons are transferred from individual cells through a network of cytochromes associated with cell outer membranes, within extracellular polymeric substances, and along pili. Here, we describe what is known about this extracellular electron transfer process, referred to as electron superexchange, and its proposed role in biofilm anode respiration. Superexchange is able to account for many different types of experimental results, as well as for the upper limit to biofilm thickness and catalytic activity that Geobacter biofilm anodes can achieve.Long-range superexchange: We describe an evolving scheme of biofilm anode respiration ultimately controlled by superexchange among extracellular cytochromes. Although it is likely that other components are also involved, we are able to account for many different types of experimental evidence reported for actively respiring Geobacter biofilm anodes.
Microbial bioelectrochemical systems (BESs) employ whole microorganisms to catalyze electrode reactions. BESs allow electricity generation from wastewater, electricity-driven (bio)production, biosensing, and bioremediation. Many of these processes are perceived as highly promising; however, to date the performance of particularly bioproduction processes is not yet at the level required for practical applications. Critical to enabling high catalytic activity are the electrochemically active microorganisms. Whether the biocatalyst comes as a planktonic cell, a surface monolayer of cells, or a fully developed biofilm, effective electron transfer and process performance need to be achieved. However, despite many different approaches and extensive research, many questions regarding the functioning of electroactive microorganisms remain open. This is certainly due to the complexity of bioelectrochemical processes, as they depend on microbial, electrochemical, physical-chemical, and operational considerations. This versatility and complexity calls for a plethora of analytical tools required to study electrochemically active microorganisms, especially biofilms. Here, we present an overview of the parameters defining electroactive microbial biofilms (EABfs) and the analytical toolbox available to study them at different levels of resolution. As we will show, a broad diversity of techniques have been applied to this field; however, these have often led to conflicting information. Consequently, to alleviate this and further mature the field of BES research, a standardized framework appears essential.From data to information: The techniques and methods used for the study of electroactive biofilm (EABf) research are summarized together with their respective level of analysis. Therefrom it is demonstrated that a unified framework of standards on EABf cultivation, operation, and analysis is needed.
The discovery that Geobacter sulfurreducens can produce protein filaments with metallic-like conductivity, known as microbial nanowires, that facilitate long-range electron transport is a paradigm shift in biological electron transfer and has important implications for biogeochemistry, microbial ecology, and the emerging field of bioelectronics. Although filaments in a wide diversity of microorganisms have been called microbial nanowires, the type?IV pili of G. sulfurreducens and G. metallireducens are the only filaments that have been shown to be required for extracellular electron transport to extracellular electron acceptors or for conduction of electrons through biofilms. Studies of G. sulfurreducens pili preparations and intact biofilms under physiologically relevant conditions have provided multiple lines of evidence for metallic-like conduction along the length of pili and for the possibility of pili networks to confer high conductivity within biofilms. This mechanism of electron conduction contrasts with the previously known mechanism for biological electron transfer via electron tunneling or hopping between closely associated molecules, a strategy unlikely to be well adapted for long-range electron transport outside the cell. In addition to promoting electron exchange with abiotic electron acceptors, microbial nanowires have recently been shown to be involved in direct interspecies electron transfer between syntrophic partners. An improved understanding of the mechanisms for metallic-like conductivity in microbial nanowires, as well as engineering microorganisms with desirable catalytic abilities with nanowires, could lead to new applications in microbial electrosynthesis and bioelectronics.Live wires: This concept article summarizes the current understanding of how microbial nanowires (see graph; scale bar: 100?nm) function, where they can be found, and their potential practical applications in bioenergy and bioelectronics.
The number of investigations involving bioelectrochemical systems (BES), processes in which microorganisms catalyze electrode reactions, is increasing while their mechanisms remain unresolved. Geobacter sulfurreducens strain DL1 is a model electrode catalyst that forms multimicrobe-thick biofilms on anodes that catalyze the oxidation of acetate to result in an electric current. Here, we report the characterization by cyclic voltammetry (CV) of DL1 biofilm-modified anodes (biofilm anodes) performed during biofilm development. This characterization, based on our recently reported model of biofilm anode catalytic activity, indicates the following. 1)?As a biofilm grows, catalytic activity scales linearly with the amount of anode-accessible redox cofactor in the biofilm. This observation is consistent with a catalytic activity that is limited during biofilm growth by electron transport from within cells to the extracellular redox cofactor. 2)?Distinct voltammetric features are exhibited that reflect the presence of a redox cofactor expressed by cells that initially colonize an anode that is not involved in catalytic current generationCycles move microbes: Long range electron transport in anode biofilms of microbial fuel cells has been studied with Geobacter sulfurreducens as a model microorganism. Cyclic voltammetry (CV) is used to model the mechanism of catalytic activity of the microbes during biofilm anode development based on our previously published five-step model. CVs recorded at various stages of biofilm growth reveal that the mechanism of catalytic activity is the same throughout biofilm development.
Microbial biocathodes allow converting and storing electricity produced from renewable sources in chemical fuels (e.g., H2) and are, therefore, attracting considerable attention as alternative catalysts to more expensive and less available noble metals (notably Pt). Microbial biocathodes for H2 production rely on the ability of hydrogenase-possessing microorganisms to catalyze proton reduction, with a solid electrode serving as direct electron donor. This study provides new chemical and electrochemical data on the bioelectrocatalytic activity of Desulfovibrio species. A combination of chronoamperometry, cyclic voltammetry, and impedance spectroscopy tests were used to assess the performance of the H2-producing microbial biocathode and to shed light on the involved electron transfer mechanisms. Cells attached onto a graphite electrode were found to catalyze H2 production for cathode potentials more reducing than ?900?mV vs. standard hydrogen electrode. The highest obtained H2 production was 8?mmol?L?1 per day, with a Coulombic efficiency close to 100?%. The electrochemical performance of the biocathode changed over time probably due to the occurrence of enzyme activation processes induced by extended electrode polarization. Remarkably, H2 (at least up to 20?% v/v) was not found to significantly inhibit its own production.Electrons as pasture for microbes: Feeding microbes with electricity offers new opportunities for storing renewable electrical energy in chemical fuels like hydrogen. By applying a combination of chemical and electrochemical techniques, new insights into the unique capacity of Desulfovibrio sp. to accept electrons from a polarized cathode and use them to catalyze the hydrogen production reaction have been obtained.
So close, but yet so far:G. sulfurreducens c-type cytochromes become reduced as biofilms grow on electrodes beyond a few cell thicknesses, even if the electrode is poised well above the potential required to oxidize all cytochromes. Cytochrome redox state also lags behind rapid potential changes during voltammetry, but only when the films are multiple cell layers thick, as would be expected if diffusional or exchange-based kinetics controls electron transfer between cytochromes.
The expression of genes involved in central metabolism and extracellular electron transfer was examined in real-time in current-producing anode biofilms of Geobacter sulfurreducens. Strains of G. sulfurreducens were generated, in which the expression of the gene for a short half-life fluorescent protein was placed under control of the promoter of the genes of interest. Anode biofilms were grown in a chamber that permitted direct examination of the cell fluorescence with confocal scanning laser microscopy. Studies on nifD and citrate synthase expression in response to environmental changes demonstrated that the reporter system revealed initiation and termination of gene transcription. Uniform expression throughout the biofilms was noted for the genes for citrate synthase; PilA, the structural protein of the conductive pili; and OmcZ, a c-type cytochrome essential for optimal current production, which was localized at the anode-biofilm interface. These results demonstrate that even cells at great distance from the anode, or within expected low-pH zones, are metabolically active and likely to contribute to current production and that there are factors other than gene expression differences influencing the distribution of OmcZ. This real-time reporter approach is likely to be a useful tool in optimizing the design of technologies relying on microbe-electrode interactions.Spotlighting gene expression: Bacterial metabolism and extracellular electron transfer are essential to the function of microbial electric systems. We report the development of a reporter system for use within current-producing Geobacter sulfurreducens biofilms allowing real-time in?situ gene expression monitoring. This reporter system is likely to be a useful tool for optimizing technologies reliant on microbe-electrode interactions.
Physical crosslinking: A typical trade-off between ionic conductivity and dimensional stability exists in hydroxides as well as in proton exchange membranes. In their Communication on page 843, Y.?S. Yan et?al. report a simple and effective strategy which utilizes direct tuning of van der Waals interactions among polymer chains to successfully reduce membrane-swelling and increase hydroxide-conductivity. This Communication, as well as the other papers in this issue of ChemSusChem, form part of a Special Issue in collaboration with the Dalian Institute of Physics, Chinese Academy of Sciences.
The Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences conducts fundamental and applied research towards chemistry and chemical engineering, with strong competence in the development of new technologies. The research in this special issue, containing 19 papers, features some of the DICP?s best work on sustainable energy, use of environmental resources, and advanced materials within the framework of the Dalian National Laboratory for Clean Energy (DNL).
The thermochemical conversion of lignocellulosic biomass feedstocks offers an important potential route for the production of biofuels and value-added green chemicals. Pyrolysis is the first phenomenon involved in all biomass thermochemical processes and it controls to a major extent the product composition. The composition of pyrolysis products can be affected markedly by the extent of softening that occurs. In spite of extensive work on biomass pyrolysis, the development of fluidity during the pyrolysis of biomass has not been quantified. This paper provides the first experimental investigation of proton mobility during biomass pyrolysis by in?situ 1H?NMR spectroscopy. The origin of mobility is discussed for cellulose, lignin and xylan. The effect of minerals on cellulose mobility is also investigated. Interactions between polymers in the native biomass network are revealed by in?situ 1H?NMR analysis.Biomass becomes fluid: An understanding of biomass pyrolysis mechanisms is of great importance for the production of biofuels and green chemicals. The pyrolysis products are highly affected by the mobility of protons. Mobility of the protons is mainly produced by the thermal conversion of lignin and xylan. Interactions between polymers in the native biomass network are evidenced.
To scale-up microbial fuel cells (MFCs), installing multiple unit cells in a common reactor has been proposed; however, there has been a serious potential drop when connecting unit cells in series. To determine the source of the loss, a basic stack-MFC (BS-MFC) has been devised, and the results show that the phenomenon is due to ions on the anode electrode traveling through the electrolyte to be reduced at the cathode connected in series. As calculated by means of the percentage potential drop, the degree of potential drop decreased with an increase in the unit-cell distance. When the distance was increased from 1 to 8?cm, the percentage potential drop in BS-MFC1 decreased from 46.76±0.90 to 45.08±0.70?% and in BS-MFC2 from 46.41±0.95 to 43.82±2.23?%. As the p-value of the t-test was lower than 0.05, the difference was considered significant; however, if the unit cells are installed far enough from each other to avoid the potential drop phenomenon, the system will be less dense, consequently reducing the ratio of electrode area per volume of anode compartment and decreasing the power density of the system. Finally, this study suggests design criteria for scaling-up MFC systems: Multiple-electrode-installed MFCs are modularized, and the unit cells are connected in series across the module (connecting each unit cell does not share the anolyte).Do stuffed cells drop? One of the biggest drawbacks of installing multiple unit cells in one reactor for scaling-up microbial fuel cell (MFC) systems is a potential drop occurring in the series connection of each unit cell. Several methods for alleviation cannot be applied to a large-scale MFC. Therefore, a design criterion—modularization—is proposed to increase the capacity of fuel utilization, concomitant with avoiding the potential drop.
Industrial nitriles from biomass: Vanadium-chloroperoxidase is successfully used to transform selectively glutamic acid into 3-cyanopropanoic acid, a key intermediate for the synthesis of bio-succinonitrile and bio-acrylonitrile, by using a catalytic amount of a halide salt. This clean oxidative decarboxylation can be applied to mixtures of amino acids obtained from plant waste streams, leading to easily separable nitriles.
Supercapacitors, which are attracting rapidly growing interest from both academia and industry, are important energy-storage devices for acquiring sustainable energy. Recent years have seen a number of significant breakthroughs in the research and development of supercapacitors. The emergence of innovative electrode materials (e.g., graphene) has clearly provided great opportunities for advancing the science in the field of electrochemical energy storage. Conversely, smart configurations of electrode materials and new designs of supercapacitor devices have, in many cases, boosted the electrochemical performance of the materials. We attempt to summarize recent research progress towards the design and configuration of electrode materials to maximize supercapacitor performance in terms of energy density, power density, and cycle stability. With a brief description of the structure, energy-storage mechanism, and electrode configuration of supercapacitor devices, the design and configuration of symmetric supercapacitors are discussed, followed by that of asymmetric and hybrid supercapacitors. Emphasis is placed on the rational design and configuration of supercapacitor electrodes to maximize the electrochemical performance of the device.Charged and ready to go: In the past few years, significant breakthroughs in the development of supercapacitors as energy-storage devices is promoted by the emergence of innovative electrode materials (e.g., graphene) and driven by rapidly increasing demands for high-performance energy-storage devices (see picture; ASC/SSC=asymmetric/symmetric supercapacitor.
The conversion of lignin, the most recalcitrant of the biopolymers, is necessary for a carbon-efficient utilization of lignocellulosic materials. In this context, hydrogenolysis of lignin is a process receiving increasing attention. In this report, the solvent effects on the hydrogenolysis of diphenyl ether and lignin with Raney Ni are addressed. The Lewis basicity of the solvent very much affects the catalytic activity, so Raney Ni in nonbasic solvents is an extremely active catalyst for hydrogenolysis and hydrogenation. In basic solvents, however, Raney Ni is a less active, but much more selective catalyst for hydrogenolysis while preserving the aromatic products. With regard to the reactions with lignin, assessing the complexity of the product mixtures by two-dimensional GC×GC–MS revealed solvent effects on the product distribution. Reaction in methylcyclohexane resulted in cyclic alcohols and cyclic alkanes, whereas reaction in 2-propanol led to cyclic alcohols, cyclic ketones, and unsaturated products. The hydrogenolysis of lignin in methanol, however, produced mostly phenols. Overall, these results demonstrate that the solvent plays a key role in directing the selectivity and, thus, it must be taken into consideration in the design of catalytic systems for conversion of lignin by hydrogenolysis of CO ether bonds.Solvents are not bystanders: The Lewis basicity of the solvent very much affects the catalytic activity of Raney nickel, so in nonbasic solvents the catalyst is an extremely active catalyst for hydrogenolysis and hydrogenation. In basic solvents, however, Raney nickel is a less active, but much more selective catalyst for hydrogenolysis while preserving the aromatic products.
The average molecular weight of cellulose derived from filter paper, poplar, and Avicel decreases by up to two orders of magnitude during typical mild dissolution protocols using ionic liquids (ILs). About an order of magnitude greater cellulose depolymerization rate during ionic liquid dissolution occurs in 1-butyl-3-methylimidazolium chloride (BmimCl) and 1-ethyl-3-methylimidazolium chloride (EmimCl) compared to 1-ethyl-3-methylimidazolium acetate (EmimOAc), and, unintuitively, greater IL purity results in greater cellulose depolymerization. The following data support the mechanism of cellulose hydrolysis to be acid-catalyzed: (i)?increase in number of reducing ends following cellulose dissolution in IL; (ii)?addition of N-methylimidazolium base suppresses cellulose depolymerization during dissolution in IL; (iii)?small amounts of glucose and traces of hydroxymethyl furfural are present following cellulose dissolution in IL. The acid is presumably synthesized via IL decomposition to generate a carbene and proton, consistent with hypothesis derived from molecular modeling. Titration experiments conducted here measure the amount of acid synthesized to be in the 4000?ppm range for high-purity BmimCl IL during mild processing conditions for cellulose dissolution. This data is relevant for understanding the extent of IL decomposition during biomass dissolution.Break it down: The average molecular weight of cellulose derived from different sources (filter paper, poplar, and Avicel) decreases by up to two orders of magnitude during typical mild dissolution protocols using ionic liquids (ILs). Counter-intuitively, greater IL purity results in greater cellulose depolymerization. The data suggest an acid-catalyzed cellulose hydrolysis mechanism, in which the acid is presumably synthesized via IL decomposition to generate a carbene and proton.
Nickel phosphide catalysts supported on activated carbon were tested for the conversion of cellulose in water. High sorbitol yields of over 60?% were obtained with high cellulose conversions at 503?K and 5?MPa of H2. It is interesting that an amorphous nickel phosphide phase is generated from a crystalline phase during the increase in temperature and that the amorphous phase is responsible for the high yield of sorbitol. The optimization of the reaction parameters indicates that the increase of the amorphous part in the cellulose is the key to obtaining high yields of sorbitol. A phase change of the nickel phosphide is observed, which can be correlated to the change in catalytic activity.Localized phosphide destroys cellulose: Carbon-supported amorphous nickel phosphide (ANP) allows the transformation of cellulose into sugar alcohols (especially sorbitol) to proceed efficiently. ANP is generated in?situ from its crystalline form during the reaction. The high activity of the catalysts is attributed to the in?situ-generated ANP phase. Modification of the carbon support improves the stability of the catalyst and reduces leaching of the catalyst.
Nitrogen-doped carbon materials are synthesized via an effective, sustainable, and green one-step route based on the hydrothermal carbonization of microalgae with high nitrogen content (ca. 11?wt?%). The addition of the monosaccharide glucose to the reaction mixture is found to be advantageous, enhancing the fixation of nitrogen in the synthesized carbons, resulting in materials possessing nitrogen content in excess of 7?wt?%, and leading to promising reaction yields. Increasing the amount of glucose leads to a higher nitrogen retention in the carbons, which suggests co-condensation of the microalgae and glucose-derived degradation/hydrolysis products via Maillard-type cascade reactions, yielding nitrogen-containing aromatic heterocycles (e.g., pyrroles) as confirmed by several analytical techniques. Increasing the HTC processing temperature leads to a further aromatization of the chemical structure of the HTC carbon and the formation of increasingly more condensed nitrogen-containing functional motifs (i.e., pyridinic and quaternary nitrogen).Keeping it in: Hydrothermal carbonization of microalgae/glucose mixtures is a green, sustainable, and economical route to synthesize nitrogen-doped carbons. The nitrogen contents are in the range of 7–8?wt?%. The nitrogen is stored in stable heterocyclic aromatic structures, such as pyrroles, pyridines, and quaternary nitrogen species, which further translates in the preservation of nitrogen content when the material is pyrolyzed.
Photo opportunity: A highly efficient and stable hybrid artificial photosynthetic H2 evolution system is assembled by using a semiconductor (ZnS) as light-harvester and an [Fe2S2] hydrogenase mimic ([(?-SPh-4-NH2)2Fe2(CO)6]) as catalyst for H2 evolution. Photocatalytic H2 production is achieved with more than 2607 turnovers (based on [Fe2S2]) and an initial turnover frequency of 100?h?1 through the efficient transfer of photogenerated electrons from ZnS to the [Fe2S2] complex.
Durability is an important issue in proton-exchange membrane fuel cells (PEMFCs). One of the major challenges lies in the degradation caused by the oxidation of the carbon support under high anode potentials (under fuel starvation conditions). Herein, we report highly stable, carbon-free, WO3 nanoclusters as catalyst supports. The WO3 nanoclusters are synthesized through a hard template method and characterized by means of electron microscopy and electrochemical analysis. The electrochemical studies show that the WO3 nanoclusters have excellent electrochemical stability under a high potential (1.6?V for 10?h) compared to Vulcan XC-72. Pt nanoparticles supported on these nanoclusters exhibit high and stable electrocatalytic activity for the oxidation of hydrogen. The catalyst shows negligible loss in electrochemically active surface area (ECA) after an accelerated durability test, whereas the ECA of the Pt nanoparticles immobilized on conventional carbon decreases significantly after the same oxidation condition. Therefore, Pt/WO3 could be considered as a promising alternative anode catalyst for PEMFCs.Tungsten substitute in a game of fuel cells: Highly stable, carbon-free, WO3 nanoclusters are synthesized as Pt supports for anodic proton-exchange membrane fuel cell (PEMFC) catalysts. Electrochemical studies show that the Pt/WO3 catalyst exhibits a high and stable electrocatalytic activity for the oxidation of hydrogen and could be considered as a promising alternative anode catalyst for PEMFCs.
A solar-energy-driven biomass fuel cell for the production of electricity from wastewater using only air and light as additional resources is described. The device consists of a photoelectrochemical cell that contains a nanostructured titanium dioxide or tungsten trioxide film as photoanode and a platinum air electrode as cathode, in separate compartments. The TiO2 or WO3 films are fabricated from TiO2 nanocrystals or from sodium tungstate solutions on top of fluorine-doped tin dioxide. Devices were tested with electrolyte only, synthetic wastewater, or with aqueous glucose solution, under irradiation with sunlight, broad spectral illumination, and monochromatic light. Measured light conversion efficiencies were between 0.007?% and 1.7?%, depending on conditions. The highest efficiency (1.7?%) and power output (0.73?mW?cm?2) are determined for TiO2 electrodes under 395?nm illumination. In contrast to TiO2, the WO3 electrodes are active under visible light (>440?nm), but the IPCE value is low (2?%). Apart from limited visible-light absorption, the overall performance of the device is limited by the substrate concentration in the water and by transport resistance through the cell.Power from waste: Treatment of municipal waste water in the US consumes $25 Billion annually and a significant fraction of US energy. Here, we describe systematic studies on TiO2/Pt and WO3/Pt photoelectrochemical cells that can oxidize organic water contaminants with artificial light or with sunlight while generating electricity at the same time.
What a swell for hydroxides: The typical trade-off between swelling control and ion conductivity in ion-conducting polymer membranes is overcome by enhancement of van der Waals interactions among polymer chains. Using a quaternary phosphonium-functionalized polymer, the simple combination of high electron density of the polymer and large dipole moment of the functional group leads to low membrane swelling, high hydroxide conductivity, and excellent hydroxide exchange membrane fuel cell performance.
Herein, poly[2,2?-(p-oxydiphenylene)-5,5?-benzimidazole] (PBI) is synthesized from 3,3?-diaminobenzidine and 4,4?-oxybisbenzoic acid, and the membrane is prepared by solvent casting. The main characteristics of PBI are studied. In the preparation of the PBI/H3PO4 composite membrane, the absorbing temperature of H3PO4 is 120?°C, which leads to a membrane with a high content of H3PO4. Membrane electrode assemblies (MEAs) are fabricated from PBI/H3PO4 membranes with the catalyst layer made of Pt/C, PBI, and polyvinylidene fluoride (230:12:7 w/w). The fabricated MEA is tested at 150?°C with dry hydrogen and oxygen gas at 0.2?MPa for both anode and cathode feeds. No degradation of voltage is seen during stability testing of the PBI/H3PO4 membrane at a constant current for 100?h. The maximum power density is 1.17?W?cm?2, and the maximum current density is 6.0?A?cm?2 with a Pt loading of 0.5?mg?cm?2. The high performance of these membrane materials demonstrates that PBI can be regarded as an alternative membrane material for high-temperature proton-exchange-membrane fuel cells.The days of Nafion are over? The performance of a PBI/H3PO4 composite membrane fuel cell is studied. A maximum power density can be achieved at a relatively low Pt loading, and maximum current density is higher than 6.0?A?cm?2. Additionally, no degradation of voltage is seen during stability testing of PBI/H3PO4 membranes at a constant current for 100?h (see figure).
Microbial fuel cells (MFCs) and other bioelectrochemical systems are new technologies that require expertise in a variety of technical areas, ranging from electrochemistry to biological wastewater treatment. There are certain data and critical information that should be included in every MFC study, such as specific surface area of the electrodes, solution conductivity, and power densities normalized to electrode surface area and volumes. Electrochemical techniques such as linear sweep voltammetry can be used to understand the performance of the MFC, but extremely slow scans are required for these biological systems compared to more traditional fuel cells. In this Minireview, the critical information needed for MFC studies is provided with examples of how results can be better conveyed through a full description of materials, the use of proper controls, and inclusion of a more complete electrochemical analysis.Electromicrobiology: The study of microbial fuel cells (MFCs) and other types of bioelectrochemical systems have great potential for renewable energy production. Certain data are essential for these systems, such as electrode-specific surface areas, solution conductivities, power densities, and electrochemical characterization. This Minireview describes how results can be better conveyed through the full description of materials, the use of proper controls, and electrochemical analyses.
Lignin is a copious paper and pulping waste product that has the potential to yield valuable, low molecular weight, single aromatic chemicals when strategically depolymerized. The single aromatic lignin model compounds, vanillin, guaiacol, and eugenol, were methacrylated by esterification with methacrylic anhydride and a catalytic amount of 4-dimethylaminopyridine. Methacrylated guaiacol (MG) and methacrylated eugenol (ME) exhibited low viscosities at room temperature (MG: 17?cP and ME: 28?cP). When used as reactive diluents in vinyl ester resins, they produced resin viscosities higher than that of vinyl ester–styrene blends. The relative volatilities of MG (1.05?wt?% loss in 18?h) and ME (0.96?wt?% loss in 18?h) measured by means of thermogravimetric analysis (TGA) were considerably lower than that of styrene (93.7?wt?% loss in 3?h) indicating the potential of these chemicals to be environmentally friendly reactive diluents. Bulk polymerization of MG and ME generated homopolymers with glass transition temperatures (Tgs) of 92 and 103?°C, respectively. Blends of a standard vinyl ester resin with MG and ME (50?wt?% reactive diluent) produced thermosets with Tgs of 127 and 153?°C, respectively, which are comparable to vinyl ester–styrene resins, thus demonstrating the ability of MG and ME to completely replace styrene as reactive diluents in liquid molding resins without sacrificing cured-resin thermal performance.Glassy lignin makes good resins: Lignin model compounds have been methacrylated and utilized as reactive diluents in a vinyl ester-based resin without the need to include the traditionally used reactive diluent styrene. The glass transition temperatures of the cured resins are comparable to those containing styrene, demonstrating the ability of these lignin model compounds to completely replace styrene as reactive diluents in liquid molding resins without sacrificing thermal performance.
Pd nanoparticles have been generated by performing an electroless procedure on a mixed ceria (CeO2)/carbon black (Vulcan XC-72) support. The resulting material, Pd–CeO2/C, has been characterized by means of transmission electron microscopy (TEM), inductively coupled plasma atomic emission spectroscopy (ICP–AES), and X-ray diffraction (XRD) techniques. Electrodes coated with Pd–CeO2/C have been scrutinized for the oxidation of ethanol in alkaline media in half cells as well as in passive and active direct ethanol fuel cells (DEFCs). Membrane electrode assemblies have been fabricated using Pd–CeO2/C anodes, proprietary FeCo cathodes, and Tokuyama anion-exchange membranes. The monoplanar passive and active DEFCs have been fed with aqueous solutions of 10?wt?% ethanol and 2?M KOH, supplying power densities as high as 66?mW?cm?2 at 25?°C and 140?mW?cm?2 at 80?°C. A comparison with a standard anode electrocatalyst containing Pd nanoparticles (Pd/C) has shown that, at even metal loading and experimental conditions, the energy released by the cells with the Pd–CeO2/C electrocatalyst is twice as much as that supplied by the cells with the Pd/C electrocatalyst. A cyclic voltammetry study has shown that the co-support ceria contributes to the remarkable decrease of the onset oxidation potential of ethanol. It is proposed that ceria promotes the formation at low potentials of species adsorbed on Pd, PdI-OHads, that are responsible for ethanol oxidation.Energizing Ce: We report the first examples of direct ethanol fuel cells containing anode electrocatalysts made of Pd nanoparticles supported on ceria (Pd–CeO2/C). A comparison with a standard anode electrocatalyst containing Pd nanoparticles (Pd/C) shows that, at the same metal loading and experimental conditions, the energy released by the cells with the Pd–CeO2/C electrocatalyst is twice as much as that supplied by the cells with the Pd/C electrocatalyst.
In this work, we found that lignosulfonic acid (LS), which is a waste byproduct from the paper industry, in ionic liquids (ILs) can catalyze the dehydration of fructose and inulin into 5-hydroxymethylfurfural (HMF) efficiently, which is a promising potential substitute for petroleum-based building blocks. The effects of reaction time, temperature, catalyst loading, and reusability of the catalytic system were studied. It was found that a 94.3?% yield of HMF could be achieved in only 10?min at 100?°C under mild conditions. The reusability study of the LS–IL catalytic system after removal of HMF by ethyl acetate extraction demonstrated that the catalytic activity decreased from 77.4 to 62.9?% after five cycles and the catalytic activity could be recovered after simply removing the accumulated humins by filtration after adding ethanol to the LS–ILs. The integrated utilization of a biorenewable feedstock, catalyst, and ILs is an example of an ideal green chemical process.Paper power: The dissolution of lignosulfonic acid, which is a waste byproduct from the paper industry, in ionic liquids is efficient for the acid-catalyzed dehydration of fructose and inulin into 5-hydroxymethylfurfural (HMF). Very high yields of HMF from fructose can be achieved in only 10?min under mild conditions (see picture) and catalytic activity can be easily recovered.
The dehydration reaction of glycerol to acrolein is catalyzed by acid catalysts. These catalysts tend to suffer from the formation of carbonaceous species on their surface (coking), which leads to substantial degradation of their performances (deactivation). To regenerate the as-deactivated catalysts, various techniques have been proposed so far, such as the co-feeding of oxygen, continuous regeneration by using a moving catalytic bed, or alternating between reaction and regeneration. Herein, we study the regeneration of supported heteropolyacid catalysts. We show that the support has a strong impact on the thermal stability of the active phase. In particular, zirconia has been found to stabilize silicotungstic acid, thus enabling the nondestructive regeneration of the catalyst. Furthermore, the addition of steam to the regeneration feed has a positive impact by hindering the degradation reaction by equilibrium displacement. The catalysts are further used in a periodic reaction/regeneration process, whereby the possibility of maintaining long-term catalytic performances is evidenced.Catalytic support: The regeneration of supported silicotungstic acid, widely used in the dehydration of glycerol to yield acrolein, is described. The nature of the support has a strong impact on the thermal stability of the active phase. Zirconia stabilizes silicotungstic acid, thus enabling efficient and nondestructive regeneration (see picture).
An efficient catalytic system for biomass oxidation to form formic acid was developed. The conversion of glucose to formic acid can reach up to 52?% yield within 3?h when catalyzed by 5?mol?% of H5PV2Mo10O40 at only 373?K using air as the oxidant. Furthermore, the heteropolyacid can be used as a bifunctional catalyst in the conversion of cellulose to formic acid (yield=35?%) with air as the oxidant.Breathing life into new conversions: An efficient conversion of biomass-derived carbohydrates into formic acid (FA) can be achieved when catalyzed by H5PV2Mo10O40, which can also be used for the conversion of cellulose into FA. X-ray photoelectron spectra and reactions of possible intermediates indirectly shed light on the reaction mechanism involving electron and oxygen transfer processes.
Acrolein is an important chemical intermediate for many common industrial chemicals, leading to an array of useful end products. This paper reviews all the synthetic methods, including the former (aldol condensation) and contemporary (partial oxidation of propylene) manufacturing methods, the partial oxidation of propane, and most importantly, the bio-based glycerol-dehydration route. Emphasis is placed on the petroleum-based route from propylene and the bio-based route from glycerol, an abundantly available and relatively inexpensive raw material available from biodiesel production. This review provides technical details and incentives for industrial proyduction that justify a transition toward bio-based acrolein production.Worthwhile glycerol: Biodiesel production and production capacity worldwide are increasing every year because of regulatory and socioeconomic motivations for renewable energy. Development of value-added chemicals from glycerol, the coproduct with biodiesel, is necessary to help sustain the biodiesel industry. Acrolein is a good example; its production from glycerol offers a promising alternative to the commercial method from propylene.
Nickel oxide and mixed-metal oxide structures were fabricated by using microwave irradiation in pure water. The nickel oxide self-assembled into unique rose-shaped nanostructures. These nickel oxide roses were studied by performing electron tomography with virtual cross-sections through the particles to understand their morphology from their interior to their surface. These materials exhibited promising performance as nanocatalysts for CO oxidation and in energy storage devices.A rose of nickel oxide on the desert: A convenient synthetic protocol for the production of nickel oxide with a unique nanorose morphology under microwave irradiation conditions has been developed, which enables the design of new catalysts by tuning the shapes and morphologies of the materials. The obtained nanostructures are single crystals composed of nanosheets and can be used as catalyst for CO oxidation and as energy storage materials.
HI returns: Hydroiodic acid is a highly selective reducing reagent for a wide variety of substrates. Its application is limited by the formation of iodine and the difficulty in reconverting that iodione back to HI in?situ. We report the facile conversion of I2 to HI by metal-catalyzed hydrogenation in the presence of water, and demonstrate the utility of this process in the conversion of fructose to 5-methyfurfural and glycerol to 2-iodopropane.
The use of cellulose is hampered by difficulties with breaking up the biopolymer into soluble products. Herein, we show that the impregnation of cellulosic substrates with catalytic amounts of a strong acid (e.g., H2SO4, HCl) is a highly effective strategy for minimizing the contact problem commonly experienced in mechanically assisted, solid-state reactions. Milling the acid-impregnated cellulose fully converts the substrate into water-soluble oligosaccharides within 2?h. In aqueous solution, soluble products are easily hydrolyzed at 130?°C in 1?h, leading to 91?% conversion of the glucan fraction of ?-cellulose into glucose, and 96?% of the xylans into xylose. Minor products are glucose dimers (8?%), 5-hydroxymethylfurfural (1?%) and furfural (4?%). Milling practical feedstocks (e.g., wood, sugarcane bagasse, and switchgrass) also results to water-soluble products (oligosaccharides and lignin fragments). The integrated approach (solid-state depolymerization in combination with liquid-phase hydrolysis) could well hold the key to a highly efficient “entry process” in biorefinery schemes.Reactive milling: The impregnation of cellulosic substrates with catalytic amounts of strong acid minimizes the contact problems encountered in mechanically assisted, solid-state reactions. As a result, full conversion of cellulose into water-soluble oligosaccharides is achieved by milling within 2?h. Water-soluble products are easily hydrolyzed at 130?°C in 1?h, leading to 91?% conversion of the glucan fraction of the substrate into glucose, and 96?% of the xylans into xylose (see picture).
On Her Majesty?s Secrete Service: Oxygen reduction is an important process for microbial fuel cells (MFCs) and microbiologically-influenced corrosion (MIC). We demonstrate that flavins secreted by anode-respiring Shewanella cells can catalyze cathodic oxygen reduction via adsorption on the cathode. The findings will provide new insight for developing methods to improve MFC performance and to prevent MIC.
Inside job: New applications of carbon materials pave the way towards greener chemical syntheses. The encapsulation of metallic Fe within CNTs improves electron transfer between the metal and the CNTs. The resulting material offers a high catalytic activity and easy magnetic separation of catalyst in the heterogeneous selective oxidation of cyclohexane.
A novel CO2 solid sorbent was prepared by synthesizing and modifying AlOOH-supported CaAl layered double hydroxides (CaAl LDHs), which were prepared by using mesoporous alumina (?-Al2O3) and calcium chloride (CaCl2) in a hydrothermal urea reaction. The nanostructured CaAl LDHs with nanosized platelets (3–30?nm) formed and dispersed inside the crystalline framework of mesoporous AlOOH (boehmite). By calcination of AlOOH-supported LDHs at 700?°C, the mesoporous CaAl metal oxides exhibited ordered hexagonal mesoporous arrays or uniform nanotubes with a large surface area of 273?m2?g?1, a narrow pore size distribution of 6.2?nm, and highly crystalline frameworks. The crystal structure of the calcined mesoporous CaAl metal oxides was multiphasic, consisting of CaO/Ca(OH)2, Al2O3, and CaAlO mixed oxides. The mesoporous metal oxides were used as a solid sorbent for CO2 adsorption at high temperatures and displayed a maximum CO2 capture capacity (?45?wt?%) of the sorbent at 650?°C. Furthermore, it was demonstrated that the mesoporous CaAl oxides showed a more rapid adsorption rate (for 1–2?min) and longer cycle life (weight change retention: 80?% for 30?cycles) of the sorbent because of the greater surface area and increased number of activated sites in the mesostructures. A simple model for the formation mechanism of mesoporous metal oxides is tentatively proposed to account for the synergetic effect of CaAl LDHs on the adsorption of CO2 at high temperature.Peeling back the layers: We have successfully developed a novel mesoporous metal oxide as CO2 solid sorbent for high temperature. The sorbent is prepared by calcining mesoporous AlOOH-supported CaAl layered double hydroxides. It exhibits ordered mesoporous arrays and displays a maximum CO2 adsorption capacity, a rapid adsorption rate, longer cycle lives and, increased number of activated sites in the mesostructures (see picture).
A series of Ni-promoted W2C catalysts was prepared by means of a post-impregnation method and evaluated for the catalytic conversion of cellulose into ethylene glycol (EG). Quite different from our previously reported Ni–W2C/AC catalysts, which were prepared by using the co-impregnation method, the introduction of Ni by the post-impregnation method did not cause catalyst sintering, but resulted in redispersion of the W component, which was identified and characterized by means of XRD, TEM, and CO chemisorption. The highly dispersed Ni-promoted W2C catalyst was very active and selective in cellulose conversion into EG, with a 100?% conversion of cellulose and a 73.0?% yield in EG. The underlying reason for the enhanced catalytic performance was most probably the significantly higher dispersion of active sites on the catalyst.Disappearing cellulose: Highly dispersed Ni-promoted W2C catalysts have been prepared by a post-impregnation method and found to be very active and selective for cellulose conversion into ethylene glycol (EG). Over Ni–(W2C/AC) catalyst, total cellulose conversion with a high EG yield has been achieved. The underlying reason for the enhanced catalytic performance is most probably the significantly higher dispersion of active sites on the catalyst.
Top of the crops: The direct use of a natural three-dimensional (3D) architecture in microbial fuel cells (MFCs) is reported for the first time. Stems from the crop plant kenaf (Hibiscus cannabinus) are carbonized and used as anode material in MFCs. The current density generated by the carbon is comparable to that of other 3D anodes prepared by other methods. The renewable and low-cost characteristics of this material provide an excellent basis for large-scale application in microbial bioelectrochemcial systems.
Y2O3:Er3+ nanorods are synthesized by means of a hydrothermal method and then introduced into a TiO2 electrode in a dye-sensitized solar cell (DSSC). Y2O3:Er3+ improves infrared light harvest via up-conversion luminescence and increases the photocurrent of the DSSC. The rare earth ions improve the energy level of the TiO2 electrode through a doping effect and thus increase the photovoltage. The light scattering is ameliorated by the one-dimensional nanorod structure. The DSSC containing Y2O3:Er3+ (5?wt?%) in the doping layer achieves a light-to-electric energy conversion efficiency of 7.0?%, which is an increase of 19.9?% compared to the DSSC lacking of Y2O3:Er3+.Illuminating rare earths: Y2O3:Er3+ nanorods are introduced into a TiO2 electrode in a dye-sensitized solar cell (DSSC). Y2O3:Er3+ improves infrared light harvesting and photocurrent through up-conversion luminescence. The rare earth ions improve the energy level of the TiO2 electrode through a doping effect and thus increase the photovoltage. The DSSC doped with Y2O3:Er3+ achieves an energy conversion efficiency of 7.0?%, which is 19.9?% higher than the DSSC without Y2O3:Er3+.
Morphological control by SBA-15: The performance of catalysts for the oxygen evolution reaction (OER) depends strongly on their structural and morphological properties. An IrO2 nanomaterial with a morphology suitable for the OER is prepared by using a synthetic scheme involving a zeolite template, and shows enhanced activity and stability compared to IrO2 fabricated by the traditional Adams-fusion method.
One ring to bind them: An efficient method for synthesizing highly functionalized pyridine derivatives from diynes and nitriles is described. The reaction system involves Cp*Ru(COD)Cl/tppts-catalyzed [2+2+2] cycloaddition in pure water. Without being accompanied by diyne dimerization or trimerization byproducts, the desired products can be obtained in moderate to high yields.
Herein, we demonstrate a new approach towards the construction of supercapacitors consisting of carbon nanotubes (CNTs) and conducting polymers (ECPs) with high specific power, high specific energy, and stable cycling performance through a 3D design of a thin film of polyaniline (PANI) on an aligned small carbon nanotube (ACNT) array on household Al foils. The thin-film strategy is used to fully exploit the specific capacitance of PANI, and obtain regular pores, strong interaction between PANI and CNTs, and reduced electrical resistance for the electrodes. A facile process is developed to fabricate a highly flexible supercapacitor using this binder-free composite on household Al foil as the current collector. It exhibits high specific energy of 18.9?Wh?kg?1, high maximum specific power of 11.3?kW?kg?1 of the active material in an aqueous electrolyte at 1.0?A?g?1, and excellent rate performance and cycling stability. A high specific energy of 72.4?Wh?kg?1, a high maximum specific power of 24.9?kW?kg?1, and a good cycling performance of the active material are obtained in an organic electrolyte.Household—the basis for everything: Supercapacitors are designed and constructed with three-dimensional aligned carbon nanotubes coated by polyaniline (ACNT@PANI) on flexible and cost-effective household Al foils, in both aqueous and organic electrolytes (see figure). The regular pores of the arrays and the thin PANI film facilitated ion diffusion and charge transfer to improve the rate performance.
Noble-metal-free systems with bio-inspired diiron dithiolate mimics of the [FeFe]-hydrogenase active site, namely, [(?-pdt)Fe2(CO)5L] [pdt=propanedithiolate; L=P(CH2OH)3 (1), P(CH3)3 (2)], as water reduction catalysts with xanthene dyes as photosensitizers and triethylamine as a sacrificial electron donor were studied for visible-light-driven water reduction to hydrogen. These systems display good catalytic activities with the efficiencies in hydrogen evolution of up to 226 turnovers for 1, if Eosin Y was used as the photosensitizer in an environmentally benign solvent (EtOH/H2O) after 15?h of irradiation (?>450?nm) under optimal conditions. Under all of the conditions adopted, 1 that has a water soluble phosphine ligand, P(CH2OH)3 displayed a higher efficiency than 2, which bears a PMe3 ligand. The photoinduced electron transfer in the systems was studied using fluorescence, transient absorption, time-resolved UV/Vis, and in?situ electron paramagnetic resonance (EPR) spectroscopy. A new electron-transfer mechanism is proposed for hydrogen evolution by these iron-based photocatalytic systems.Three gang up on hydrogen: Bioinspired diiron complexes, xanthene dyes, and triethylamine make up three-component systems that display high turnover numbers for the photoinduced hydrogen production. The quantum yield is determined for this catalytic system. A plausible mechanism for the formation of the FeIFe0 species is proposed, which involves the reduction of the diiron catalyst by the neutral alkyl radical photogenerated from triethylamine.
A series of Ni-promoted W2C/activated carbon (AC) catalysts were investigated for the catalytic conversion of Jerusalem artichoke tuber (JAT) under hydrothermal conditions and hydrogen pressure. Even a small amount of Ni could greatly promote the conversion of JAT to 1,2-propylene glycol (1,2-PG), whereas the pure W2C/AC catalyst resulted in the selective formation of acetol. The product distribution profiles involving the reaction temperature, time, and H2 pressure indicated that 1,2-PG formed as a result of acetol hydrogenation, which was catalyzed by Ni. Thus, there was a synergy between W2C and Ni, and the best performance yielded 38.5?% of 1,2-PG over a 4?%?Ni–20?%?W2C/AC catalyst at 245?°C, 6?MPa H2, and 80?min. To understand the reaction process, some important intermediates, such as inulin, fructose, acetol, glyceraldehyde, and 1,3-dihydroxyacetone, were used as the feedstock. Based on the product distributions derived from these intermediates, a reaction pathway was proposed, where JAT was first hydrolyzed into a mixture of fructose and glucose under the catalysis of H+, then the sugars underwent a retro-aldol reaction followed by hydrogenation catalyzed by Ni–W2C.Down to the roots with Ni: By using a combination of nickel and tungsten carbide supported on activated carbon, it is possible to convert Jerusalem artichoke tuber (JAT), a fructose-based biomass that can be used as a raw material without any pretreatment, selectively into 1,2-propylene glycol and ethylene glycol. A reasonable reaction pathway is suggested based on analysis of the product distribution under different reaction conditions and use of different feedstocks.
The methanol-to-olefins (MTO) process is becoming the most important non-petrochemical route for the production of light olefins from coal or natural gas. Maximizing the generation of the target products, ethene and propene, and minimizing the production of byproducts and coke, are major considerations in the efficient utilization of the carbon resource of methanol. In the present work, the heterogeneous catalytic conversion of methanol was evaluated by performing simultaneous measurements of the volatile products generated in the gas phase and the confined coke deposition in the catalyst phase. Real-time and complete reaction profiles were plotted to allow the comparison of carbon atom economy of methanol conversion over the catalyst SAPO-34 at varied reaction temperatures. The difference in carbon atom economy was closely related with the coke formation in the SAPO-34 catalyst. The confined coke compounds were determined. A new type of confined organics was found, and these accounted for the quick deactivation and low carbon atom economy under low-reaction-temperature conditions. Based on the carbon atom economy evaluation and coke species determination, optimized operating conditions for the MTO process are suggested; these conditions guarantee high conversion efficiency of methanol.Coke goes to prison: Heterogeneous catalysis of methanol conversion is investigated through simultaneous measurements of volatile products and confined coke deposition. Complete and real-time reaction profiles are plotted for evaluation of carbon atom economy of the conversion. The deposited coke products have been determined, and a new species has been detected, which is responsible for fast deactivation of the catalyst and low carbon atom economy at low temperatures.
Perylene diimides (PDIs) and their derivatives are active n-type semiconducting materials widely used in organic electronic devices. A series of PDI derivatives have been investigated by quantum chemistry calculations combined with Marcus–Hush electron-transfer theory. The substitution of three different sites of a PDI induces large changes in its electron-transfer mobility. 2,5,8,11-Tetrachloro-PDI with four chlorine atoms in ortho positions shows both large electron- and hole-transfer mobilities of 0.116 and 0.650?cm2?V?1?s?1, respectively, indicative of a potentially highly efficient ambipolar organic semiconducting material. The calculated electron-transfer mobility of 1,6,7,12-tetrachloro-PDI is 0.081?cm2?V?1?s?1, which is in good agreement with the experimental result. Octachloro-PDIs have the largest electron mobility among these derivatives, although the ? system of the central core is twisted. 2D ?-stacking and hydrogen bonds formed at the imide positions are responsible for the large mobility. Simulated anisotropic transport mobility curves of these materials prove the magnitude of the mobility that appears when the measuring transistor channel is along the a-axis of the crystal, which is the direction of hydrogen bond formation.Let's twist the fork: Perylene diimides (PDIs) and its derivatives are active n-type semiconducting materials widely used in organic electronic devices. This work elucidates different influences on electron-transfer mobility by substitution of PDIs in three different positions (bay-, ortho- and imide-positions) with chlorine. A fork-like structure is reported to be responsible for the large electron mobility of octachloro-PDIs with a twisted system.
Possessing high H2 capacities and interesting dehydrogenation behavior, metal amidoborane ammoniates were prepared by reacting Ca(NH2)2, MgNH, and LiNH2 with ammonia borane to form Ca(NH2BH3)2?2?NH3, Mg(NH2BH3)2?NH3, and Li(NH2BH3)2?NH3 (LiAB?NH3). Insight into the mechanisms of amidoborane ammoniate formation and dehydrogenation was obtained by using isotopic labeling techniques. Selective 15N and 2H labeling showed that the formation of the ammoniate occurs via the transfer of one H(N) from ammonia borane to the [NH2]? unit in Ca(NH2)2 giving rise to NH3 and [NH2BH3]?. Supported by theoretical calculations, it is suggested that the improved dehydrogenation properties of metal amidoborane ammoniates compared to metal amidoboranes are a result of the participation of a strong dihydrogen bond between the NH3 molecule and [NH2BH3]?. Our study elucidates the reaction pathway involved in the synthesis and dehydrogenation of Ca(NH2BH3)2?2?NH3, and clarifies our understanding of the role of NH3, that is, it is not only involved in stabilizing the structure, but also in improving the dehydrogenation properties of metal amidoboranes.Amidoborane ammoniate formation is investigated by using isotopic labeling techniques. The formation of Ca(NH2BH3)2?2?NH3 is initiated by proton transfer from NH3BH3 to NH2? (amide), forming Ca(NH3)2+ and anionic [NH2BH3]? groups. The dehydrogenation of the ammoniate, which occurs at lower temperatures, is a result of the participation of NH3 in the dehydrogenation process via the combination of (NH3)H?+???H??(NH2BH3?).
A sheltered existence: Direct liquid-membrane crystallization is used as a low-cost, low-waste, yet highly effective method to prepare a catalyst encapsulated by a H-? zeolite. Through vapor–liquid exchange, a continuous and sufficient, but not excessive supply of both water and template is the key part of this method.
Zn and the Art of Battery Development: A zinc/polyhalide redox flow battery employs Br?/ClBr2? and Zn/Zn2+ redox couples in its positive and negative half-cells, respectively. The performance of the battery is evaluated by charge–discharge cycling tests and reveals a high energy efficiency of 81%, based on a Coulombic efficiency of 96% and voltage efficiency of 84%. The new battery technology can provide high performance and energy density at an acceptable cost.
Plant–microbial fuel cells (PMFCs) are newly emerging devices, in which electricity can be generated by microorganisms that use root exudates as fuel. This review presents the development of PMFCs, with a summary of their power generation, configurations, plant types, anode and cathode materials, biofilm communities, potential applications, and future directions.Down to the roots: Plant–microbial fuel cells convert solar energy into electrical power by using microorganisms, which degrade root exudates and pollutants at the anode and pass the electrons to acceptors at the cathode. This setup can provide auxiliary power while reducing the emission of greenhouse gas, that is, methane, from fields.
The catalytic role of the PtFe cation ensemble presented at the perimeters of the FeO film supported on Pt(111) for low-temperature CO oxidation and the promotion of water on activity were studied by using DFT calculations. We found that the perimeter sites along the edge of the FeO islands on Pt provided a favorable ensemble that consisted of coordinatively unsaturated ferrous species and nearby Pt atoms for O2 and H2O activation free from CO poison. A dissociative oxygen atom at the PtFe cation ensemble reacts easily with CO adsorbed on nearby Pt. The OH group from water dissociation not only facilitates activation of the oxygen molecule, more importantly it opens a facile reaction channel for CO oxidation through the formation of the carboxyl intermediate. The presence of the OH group on the FeO film strengthens interfacial interactions between FeO and Pt(111), which would make the FeO film more resistant to further oxidation. The importance of the PtFe cation ensemble and the role of water as a cocatalyst for low-temperature CO oxidation is highlighted.An active ensemble: The PtFe cation ensemble hosted in the perimeters of FeO islands supported on Pt provides active sites for O2 and H2O activation free from CO poison. The PtFe cation ensemble is highly active for CO oxidation, the activity of which is further promoted by water (see picture).
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