The effect of addition of ZrO2 to Fe2O3 for hydrogen production by chemical looping

In this paper, a synthetic mixture of ZrO2 and Fe 2O3 was prepared by coprecipitation for use in chemical looping and hydrogen production. Cycling experiments in a fluidized bed showed that a material composed of 30 mol % ZrO2 and 70 mol % Fe 2O3 was capable of producing hydrogen with a consistent yield of 90 mol % of the stoichiometric amount over 20 cycles of reduction and oxidation at 1123 K. Here, the iron oxide was subjected to cycles consisting of nearly 100% reduction to Fe followed by reoxidation (with steam or CO 2 and then air) to Fe2O3. There was no contamination by CO of the hydrogen produced, at a lower detection limit of 500 ppm, when the conversion of Fe3O4 to Fe was kept below 90 mol %. A preliminary investigation of the reaction kinetics confirmed that the ZrO2 support does not inhibit rates of reaction compared with those observed with iron oxide alone. © 2012 American Chemical Society.

A novel hydrogen peroxide sensor based on horseradish peroxidase immobilized on colloidal Au modified ITO electrode

A novel method to fabricate a hydrogen peroxide sensor was developed by immobilizing horseradish peroxidase (HRP) on colloidal An modified ITO conductive glass support. The cleaned glass support was modified with (3-aminopropyl)trimethoxysilane (APTMS) first to yield an interface for the assembly of colloidal An. Then 15 nm colloidal Au particles were chemisorbed onto the amine groups of the APTMS. Finally, HRP was adsorbed onto the surface of the colloidal An. The immobilized HRP displayed excellent electrocatalytical response to the reduction of hydrogen peroxide. The performance and factors influencing the resulted biosensor were studied in detail. The resulted biosensor exhibited fast amperometric response (within 5 s) to H2O2. The detection limit of the biosensor was 8.0 mumol l(-1), and linear range was from 20.0 mumol l(-1) to 8.0 mmol l(-1). Furthermore, the resulted biosensor exhibited high sensitivity, good reproducibility, and long-term stability.

Modified poly(3-hydroxybutyrate-co-3-hydroxyvalerate) using hydrogen bonding monomers

Properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) were significantly modified by a hydrogen bonding (H-bond) monomer-bisphenol A (BPA). BPA lowered the T-m of PHBV and widened the heat-processing window of PHBV. At the same time, a dynamic H-bond network in the blends was observed indicating that BPA acted as a physical cross-link agent. BPA enhanced the T, of PHBV and reduced the crystallization rate of PHBV. It resulted in larger crystallites in PHBV/BPA blends showed by WAXD. However, the crystallinity of PHBV was hardly reduced. SAXS results suggested that BPA molecules distributed in the inter-lamellar region of PHBV. Finally, a desired tension property was obtained, which had an elongation at break of 370% and a yield stress of 16 MPa. By comparing the tension properties of PHBV/BPA and PHBV/tert-butyl phenol blends, it was concluded that the H-bond network is essential to the improvement of ductility.

Fe(2-EHA)(3)/Al(i-Bu)(3)/hydrogen phosphite catalyst for preparing syndiotactic 1,2-polybutadiene

Polymerizing 1,3-butadiene into syndiotactic 1,2-polybutadiene with art iron(III) catalyst system has been investigated. Activity of the catalyst was affected by the type of cocatalyst alkylaluminum and the phosphorus compound as an electron donor, molar ratio of catalyst components, and their aging sequence and aging time of the catalyst. The microstructure and configuration of the polymer was decided by the catalyst components, the higher [Al]/[Fe] molar ratio tending to yield syndiotactic 1,2-polybutadiene, while the higher [P]/[Fe] molar ratio favors the formation of amorphous 1,2-polybutadiene.

Synthesis and crystal structure of chiral bis(cyclopentadienyl) samarium Schiff base complexes bearing intramolecular C-C bond formation and hydrogen transfer

SmCl3, reacted with CpNa (Cp = Cyclopentadienyl) in the ratio of 1:3 in THF, which then was reacted with (S)-(+)-N-1-(phenylethyl) salicylideneamine/toluene to yield the title complex, [GRAPHICS] The X-ray crystal structure determination of the title complex reveals that 1 is a dimer with intramolecular C-C bond formation and hydrogen transfer, which leads to the configuration turnover of the carbon atom at the benzyl position of the ligand, while those of the newly formed asymmetric centers may have either Ii or S type configurations. (C) 1998 Elsevier Science Ltd. All rights reserved.

Fermentative hydrogen production by the new marine Pantoea agglomerans isolated from the mangrove sludge

A new fermentative hydrogen-producing bacterium was isolated from mangrove sludge and identified as Pantoea agglomerans using light microscopic examination, Biolog test and 16S rRNA gene sequence analysis. The isolated bacterium, designated as P. agglomerans BH-18, is a new strain that has never been optimized as a potential hydrogen-producing bacterium. In this study, the culture conditions and the hydrogen-producing ability of P. agglomerans BH-18 were examined. The strain was a salt-tolerant facultative anaerobe with the initial optimum pH value at 8.0-9.0 and temperature at 30 degrees C on cell growth. During fermentation, hydrogen started to evolve when cell growth entered late-exponential phase and was mainly produced in the stationary phase. The strain was able to produce hydrogen over a wide range of initial pH from 5 to 10, with an optimum initial pH of 6. The level of hydrogen production was affected by the initial glucose concentration, and the optimum value was found to be 10 g glucose/l. The maximum hydrogen-producing yield (2246 ml/l) and overall hydrogen production rate (160 ml/l/h) were obtained at an initial glucose concentration of 10 g/l and an initial pH value of 7.2 in marine culture conditions. In particular, the level of hydrogen production was also affected by the salt concentration. Hydrogen production reached a higher level in fresh culture conditions than in marine ones. In marine conditions, hydrogen productivity was 108 ml/l/h at an initial glucose concentration of 20 g/l and pH value of 7.2, whereas, it increased by 27% in fresh conditions. In addition, this strain could produce hydrogen using glucose and many other carbon sources such as fructose, sucrose, sorbitol and so on. As a result, it is possible that P. agglomerans BH-18 is used for biohydrogen production and biological treatment of mariculture wastewater and marine organic waste. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

Quantum manifestations of closed orbits in the photoexcitation scaled spectrum of the hydrogen atom in crossed fields

The scaled photoexcitation spectrum of the hydrogen atom in crossed electric and magnetic fields has been obtained by means of accurate quantum mechanical calculation using a new algorithm. Closed orbits in the corresponding classical system have also been obtained, using a new, efficient and practical searching procedure. Two new classes of closed orbit have been identified. Fourier transforming each photoexcitation quantum spectrum to yield a plot against scaled action has allowed direct comparison between peaks in such plots and the scaled action values of closed orbits, Excellent agreement has been found with all peaks assigned.

Organometallic hydrogen transfer and dehydrogenation catalysts for the conversion of bio-renewable alcohols

Organometallic hydrogen transfer and dehydrogenation provide straightforward atom efficient routes from alcohols to a variety of chemical products. The potential of these reactions to enable the conversion of biomass to value added chemicals is discussed, with reference to the products that can be prepared from aliphatic alcohols in good isolated yield.

Catalytic conversion of sodium lignosulphonate to vanillin –engineering aspects. Part 1 Effect of processing conditionson vanillin yield and selectivity

The commercial production of vanillin from sodium lignosulfonate under highly alkaline conditions, catalyzed by Cu2+ at elevated temperature and pressures up to 10 bar, has been simulated in a 3-L stirred reactor. Initially, the process was operated in the presence of nitrogen in dead-end mode, and it was shown that vanillin and vanillic acid were formed by hydrolysis at temperatures of 120, 140, and 160 °C. At the two higher temperatures, the amount of vanillin produced was the same. Subsequently, experiments were conducted at the same elevated pressures and temperatures with addition of air or oxygen-enriched air once the temperature in the reactor had reached temperatures similar to those used when only hydrolysis occurred. In this case, the concentration of vanillin at 140 and 160 °C was equal to that due to hydrolysis, and the subsequent 2-fold increase was due to oxidation. In addition, both vanillic acid and acetovanillone (which has rarely been reported) were produced, as was hydrogen. Thus, for the first time, it has been shown that the production of vanillin (and other compounds) from sodium lignosulfonate at elevated temperatures involves hydrolysis and oxidation, with hydrolysis starting at just above 100 °C, that is, much lower than has previously been reported. Approximately 50% is produced by each mechanism. In addition, the orders of the reactions of the different steps were estimated, and the reaction mechanisms are discussed.

Effects of arsenic-contaminated irrigation water on growth, yield, and nutrient concentration in rice

A study was undertaken to determine the effects of different concentrations of arsenic (As) in irrigation water on Boro (dry-season) rice (Oryza sativa) and their residual effects on the following Aman (wet-season) rice. There were six treatments, with 0, 0.1, 0.25, 0.5, 1, and 2 mg As L-1 applied as disodium hydrogen arsenate. All the growth and yield parameters of Boro rice responded positively at lower concentrations of up to 0.25 mg As L-1 in irrigation water but decreased sharply at concentrations more than 0.5 mg As L-1. Arsenic concentrations in grain and straw of Boro rice increased significantly with increasing concentration of As in irrigation water. The grain As concentration was in the range of 0.25 to 0.97 μg g-1 and its concentration in rice straw varied from 2.4 to 9.6 μg g-1 over the treatments. Residual As from previous Boro rice showed a very similar pattern in the following Aman rice, although As concentration in Aman rice grain and straw over the treatments was almost half of the As levels in Boro rice grain. Arsenic concentrations in both grain and straw of Boro and Aman rice were found to correlate with iron and be antagonistic with phosphorus. Copyright © Taylor & Francis Group, LLC.

The importance of hydrogen bonding in the alkylation of phenols

Hydrogen bond assisted alkylation of phenols is compared with the classical base assisted reactions. The influence of solvents on the fluoride assisted reactions is discussed,· with emphasis on the localization of hydrogen bond charge density. Polar aprotic solvents such as DMF favour a-alkylation, and nonpolar aprotic solvents such as toluene favourC-alkylation of phenol. For more reactive and soluble fluorides, such as tetrabu~ylammoniumfluoride, the polar aprotic solvent favours a-alkylation and nonpolar aprotic solvent favours fluorination. Freeze-dried potassium fluoride is a better catalytic agent in hydrogen bond assisted alkylation reactions of phenol than the oven-dried fluoride. The presence of water in the alkylation reactions reduces the expected yield drastically. The tolerance of the reaction to water has also been studied. The use ofa phase transfer catalyst such as tetrabutylammonium bromide in the alkylation reactions of phenol in the presence of potassium fluoride is very effective under anhydrous conditions. Sterically hindered phenols such as 2,6-ditertiarybutyl-4-methyl phenol could not be alkylated even by using the more reactive fluorides, such as tetrabutylammonium fluoride in either polar or nonpolar aprotic solvents. Attempts were also made to alkylate phenols in the presence of triphenylphosphine oxide.

Improvements in Fermentative Hydrogen Production through Physiological Manipulation and Metabolic Engineering

La production biologique d'hydrogène (H2) représente une technologie possible pour la production à grande échelle durable de H2 nécessaire pour l'économie future de l'hydrogène. Cependant, l'obstacle majeur à l'élaboration d'un processus pratique a été la faiblesse des rendements qui sont obtenus, généralement autour de 25%, bien en sous des rendements pouvant être atteints pour la production de biocarburants à partir d'autres processus. L'objectif de cette thèse était de tenter d'améliorer la production d'H2 par la manipulation physiologique et le génie métabolique. Une hypothèse qui a été étudiée était que la production d'H2 pourrait être améliorée et rendue plus économique en utilisant un procédé de fermentation microaérobie sombre car cela pourrait fournir la puissance supplémentaire nécessaire pour une conversion plus complète du substrat et donc une production plus grande d'H2 sans l'aide de l'énergie lumineuse. Les concentrations optimales d’O2 pour la production de H2 microaérobie ont été examinées ainsi que l'impact des sources de carbone et d'azote sur le processus. La recherche présentée ici a démontré la capacité de Rhodobacter capsulatus JP91 hup- (un mutant déficient d’absorption-hydrogénase) de produire de l'H2 sous condition microaérobie sombre avec une limitation dans des quantités d’O2 et d'azote fixé. D'autres travaux devraient être entrepris pour augmenter les rendements d'H2 en utilisant cette technologie. De plus, un processus de photofermentation a été créé pour améliorer le rendement d’H2 à partir du glucose à l'aide de R. capsulatus JP91 hup- soit en mode non renouvelé (batch) et / ou en conditions de culture en continu. Certains défis techniques ont été surmontés en mettant en place des conditions adéquates de fonctionnement pour un rendement accru d'H2. Un rendement maximal de 3,3 mols de H2/ mol de glucose a été trouvé pour les cultures en batch tandis que pour les cultures en continu, il était de 10,3 mols H2/ mol de glucose, beaucoup plus élevé que celui rapporté antérieurement et proche de la valeur maximale théorique de 12 mols H2/ mol de glucose. Dans les cultures en batch l'efficacité maximale de conversion d’énergie lumineuse était de 0,7% alors qu'elle était de 1,34% dans les cultures en continu avec un rendement de conversion maximum de la valeur de chauffage du glucose de 91,14%. Diverses autres approches pour l'augmentation des rendements des processus de photofermentation sont proposées. Les résultats globaux indiquent qu'un processus photofermentatif efficace de production d'H2 à partir du glucose en une seule étape avec des cultures en continu dans des photobioréacteurs pourrait être développé ce qui serait un processus beaucoup plus prometteur que les processus en deux étapes ou avec les co-cultures étudiés antérieurément. En outre, l'expression hétérologue d’hydrogenase a été utilisée comme une stratégie d'ingénierie métabolique afin d'améliorer la production d'H2 par fermentation. La capacité d'exprimer une hydrogénase d'une espèce avec des gènes de maturation d'une autre espèce a été examinée. Une stratégie a démontré que la protéine HydA orpheline de R. rubrum est fonctionnelle et active lorsque co-exprimée chez Escherichia coli avec HydE, HydF et HydG provenant d'organisme différent. La co-expression des gènes [FeFe]-hydrogénase structurels et de maturation dans des micro-organismes qui n'ont pas une [FeFe]-hydrogénase indigène peut entraîner le succès dans l'assemblage et la biosynthèse d'hydrogénase active. Toutefois, d'autres facteurs peuvent être nécessaires pour obtenir des rendements considérablement augmentés en protéines ainsi que l'activité spécifique des hydrogénases recombinantes. Une autre stratégie a consisté à surexprimer une [FeFe]-hydrogénase très active dans une souche hôte de E. coli. L'expression d'une hydrogénase qui peut interagir directement avec le NADPH est souhaitable car cela, plutôt que de la ferrédoxine réduite, est naturellement produit par le métabolisme. Toutefois, la maturation de ce type d'hydrogénase chez E. coli n'a pas été rapportée auparavant. L'opéron hnd (hndA, B, C, D) de Desulfovibrio fructosovorans code pour une [FeFe]-hydrogénase NADP-dépendante, a été exprimé dans différentes souches d’E. coli avec les gènes de maturation hydE, hydF et hydG de Clostridium acetobutylicum. L'activité de l'hydrogénase a été détectée in vitro, donc une NADP-dépendante [FeFe]-hydrogénase multimérique active a été exprimée avec succès chez E. coli pour la première fois. Les recherches futures pourraient conduire à l'expression de cette enzyme chez les souches de E. coli qui produisent plus de NADPH, ouvrant la voie à une augmentation des rendements d'hydrogène via la voie des pentoses phosphates.

Destabilizing Mutations Alter the Hydrogen Exchange Mechanism in Ribonuclease A

The effect of strongly destabilizing mutations, I106A and V108G of Ribonuclease A (RNase A), on its structure and stability has been determined by NMR. The solution structures of these variants are essentially equivalent to RNase A. The exchange rates of the most protected amide protons in RNase A (35ºC), the I106A variant (35ºC), and the V108G variant (10ºC) yield stability values of 9.9, 6.0, and 6.8 kcal/mol, respectively, when analyzed assuming an EX2 exchange mechanism. Thus, the destabilization induced by these mutations is propagated throughout the protein. Simulation of RNase A hydrogen exchange indicates that the most protected protons in RNase A and the V108G variant exchange via the EX2 regime, whereas those of I106A exchange through a mixed EX1 1 EX2 process. It is striking that a single point mutation can alter the overall exchange mechanism. Thus, destabilizing mutations joins high temperatures, high pH and the presence of denaturating agents as a factor that induces EX1 exchange in proteins. The calculations also indicate a shift from the EX2 to the EX1 mechanism for less protected groups within the same protein. This should be borne in mind when interpreting exchange data as a measure of local stability in less protected regions

Metal cluster expansion by addition of low-valent group 4B reagents: crystal and molecular structure of [Os3SnH2(CO)10{CH(SiMe3)2}2]; a compound with hydrogen bridging osmium and tin

Cluster expansion of [Os3H2(CO)10] with [SnR2][R = CH(SiMe3)2] take place in high yield to give [Os3SnH2(CO)10R2], the first closed triosmium–main-group metal cluster to be structurally characterized; a novel feature is the presence of a hydrogen atom bridging the tin atom and one of the osmium atoms.

Production of hydrogen via steam reforming of biofuels on Ni/CeO(2)-Al(2)O(3) catalysts promoted by noble metals

The catalytic activity of Ni/CeO(2)-Al(2)O(3) catalysts modified with noble metals (Pt, Ir, Pd and Ru) was investigated for the steam reform of ethanol and glycerol. The catalysts were characterized by the following techniques: Energy-dispersive X-ray, BET, X-ray diffraction, temperature-programmed reduction, UV-vis diffuse reflectance spectroscopy and X-ray absorption near edge structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of CeO(2) dispersed on alumina. The promoting effect of noble metals included a decrease in the reduction temperatures of NiO species interacting with the support, due to the hydrogen spillover effect. It was seen that the addition of noble metal stabilized the Ni sites in the reduced state along the reforming reaction, increasing the ethanol and glycerol conversions and decreasing the coke formation. The higher catalytic performance for the ethanol steam reforming at 600 degrees C and glycerol steam reforming was obtained for the NiPd and NiPt catalysts, respectively, which presented an effluent gaseous mixture with the highest H(2) yield with reasonably low amounts of CO. (c) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.