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Recent astronomical observations of both isomers E and Z of imines such as cyanomethanimine, ethanimine and 2-propyn-1-imine, have revealed that the abundances in the ISM of these isomers differ by factors of ~3-10. Several theories have been proposed to explain the observed behavior, but none of them successfully explains the [E]/[Z] ratios. In this work we present a detailed study of the kinetics of the one-step E-Z isomerization reactions of cyanomethanimine, ethanimine and 2-propyn-1-imine under interstellar conditions (in the 10-400 K temperature range). This reaction was previously thought to be non-viable in the ISM due to its associated high-energy barrier (about 13,000 K). In this Letter, we show that considering the multidimensional small curvature tunneling approximation, the tunneling effect enables the isomerization even at low temperatures. This is due to the fact that the representative tunneling energy lies in the vibrational ground state of the least stable isomer up to approximately 150 K, making the reaction constants of the isomerization from the least stable to the most stable isomer basically constant. The predicted [E]/[Z] ratios are almost the same as those reported from the astronomical observations for all imines observed. This study demonstrates that the [E]/[Z] ratio of imines in the ISM strongly depends on their relative stability., Comment: 13 pages, 2 figures

Among presolar grains, oxide ones are made of oxygen, aluminum, and a small fraction of magnesium, produced by the 26Al decay. The largest part of presolar oxide grains belong to the so-called group 1 and 2, which have been suggested to form in Red Giant Branch (RGB) and Asymptotic Giant Branch (AGB) stars, respectively. However, standard stellar nucleosynthesis models cannot account for the 17O/16O, 18O/16O, and 26Al/27Al values recorded in those grains. Hence, for more than 20 years, the occurrence of mixing phenomena coupled with stellar nucleosynthesis have been suggested to account for this peculiar isotopic mix. Nowadays, models of massive AGB stars experiencing Hot Bottom Burning or low mass AGB stars where Cool Bottom Process, or another kind of extra-mixing, is at play, nicely fit the oxygen isotopic mix of group 2 oxide grains. The largest values of the 26Al/27Al ratio seem somewhat more difficult to account for.

Experimental work at the LR-0 reactor was carried out to determine the possibility of the mock-up neutron field creation for the fluoride salt-based reactors. Previous calculations and experiments have shown that the fast part of the molten salt reactor (MSR) spectrum is shaped by fluorine and even the Teflon material is suitable for neutronics in that energy range. Properly selected spectrum indices can describe the neutron field of the MSR in fast thermal and intermediate parts of the spectrum. Current research has focused on a deeper study of the possibility of using the filtered thermal and intermediate neutron spectrum of the experimental light water reactor for the physics of fluoride salt-based reactor. LiF-BeF2 (FLIBE) capsule and teflon cylinders are used as a spectrum filters in the LR-0 reactor. Measured results show acceptable C/E-1 agreement in the reaction rates and satisfactory agreement for usage of the FLIBE filtered neutron spectrum determined by the 181Ta(n, γ) monitor as a mock-up in thermal to intermediate energy in the fluoride high-temperature reactor (FHR). Concerning MSR, intermediate spectrum can be reproduced to some extent but not as good as in the case of FHR.

Significance The interpretation of rates of reactions that take place in a solvent is complicated because of the entanglement of free-energy and history-dependent friction effects. In this context, the dihedral dynamics of butane has played a paradigmatic role since it is simple yet relevant for conformational transitions in polymers and proteins. We directly extract the friction that governs the dihedral dynamics in butane from simulations. We show that ∼89% of the total friction cannot be described as solvent friction and is caused by degrees of freedom that are orthogonal to the dihedral reaction coordinate. This shows that the hydrodynamic estimate of friction severely fails, even in the simplest molecular reaction., The dihedral dynamics of butane in water is known to be rather insensitive to the water viscosity; possible explanations for this involve inertial effects or Kramers’ turnover, the finite memory time of friction, and the presence of so-called internal friction. To disentangle these factors, we introduce a method to directly extract the friction memory function from unconstrained simulations in the presence of an arbitrary free-energy landscape. By analysis of the dihedral friction in butane for varying water viscosity, we demonstrate the existence of an internal friction contribution that does not scale linearly with water viscosity. At normal water viscosity, the internal friction turns out to be eight times larger than the solvent friction and thus completely dominates the effective friction. By comparison with simulations of a constrained butane molecule that has the dihedral as the only degree of freedom, we show that internal friction comes from the six additional degrees of freedom in unconstrained butane that are orthogonal to the dihedral angle reaction coordinate. While the insensitivity of butane’s dihedral dynamics to water viscosity is solely due to the presence of internal friction, inertial effects nevertheless crucially influence the resultant transition rates. In contrast, non-Markovian effects due to the finite memory time are present but do not significantly influence the dihedral barrier-crossing rate of butane. These results not only settle the character of dihedral dynamics in small solvated molecular systems such as butane, they also have important implications for the folding of polymers and proteins.

The low temperature reaction between CN and benzene (C$_6$H$_6$) is of significant interest in the astrochemical community due to the recent detection of benzonitrile, the first aromatic molecule identified in the interstellar medium (ISM) using radio astronomy. Benzonitrile is suggested to be a low temperature proxy for benzene, one of the simplest aromatic molecules, which may be a precursor to polycyclic aromatic hydrocarbons (PAHs). In order to assess the robustness of benzonitrile as a proxy for benzene, low temperature kinetics measurements are required to confirm whether the reaction remains rapid at the low gas temperatures found in cold dense clouds. Here, we study the C$_6$H$_6$ + CN reaction in the temperature range 15--295 K, using the well-established CRESU technique (a French acronym standing for Reaction Kinetics in Uniform Supersonic Flow) combined with Pulsed Laser Photolysis-Laser-Induced Fluorescence (PLP-LIF). We obtain rate coefficients, $k(T)$, in the range (3.6--5.4) $\times$ 10$^{-10}$ cm$^3$ s$^{-1}$ with no obvious temperature dependence between 15--295 K, confirming that the CN + C$_6$H$_6$ reaction remains rapid at temperatures relevant to the cold ISM.

Mounting evidence suggests that Criegee intermediates are important tropospheric oxidants of both organic and inorganic gases, supplementing the oxidation chemistry initiated by OH radicals. Here, the rate coefficient for reaction of the simplest Criegee intermediate CH2OO with acetone, k(CH2OO + (CH3)2CO), was measured using laser flash photolysis and cavity ring-down spectroscopy methods under tropospherically relevant conditions of pressure and temperature. The pressure dependence of k(CH2OO + (CH3)2CO)= (4.7 ± 0.1) x 10-13 [N2] / ((3.7 ± 0.7) x 1016 + [N2]) cm3 molecule-1 s-1 was measured in the 5 to 100 Torr range, returning a high-pressure limit value of (4.7 ± 0.1) x 10-13 cm3 molecule-1 s-1 at 293 K. A temperature dependence of k(CH2OO + (CH3)2CO) = (1.45 ± 0.18) x 10-21 T2 exp (2407 ± 36 / T) cm3 molecule-1 s-1 was observed in the 250 to 310 K range. The global chemical transport model (STOCHEM-CRI) was used to model the speciated Criegee intermediate field using recently reported temperature dependent rate coefficient values for various reactions of Criegee intermediates. Incorporation of the Criegee intermediate reaction with acetone in the model predicts decreases in acetone concentration of as much as 10 to 40 ppt in various regions of the world.

Traditionally, sulfide abatement has been done by adding e.g. ferrous or ferric iron salts to the start of sewer force mains. Iron dosage must hence correspond to an estimate of how much sulfide will form while the wastewater stays in the main, which is not straightforward. Adding iron salts at the end of the main has the advantage that the exact amount of sulfide to precipitate, in principle, can be known. A drawback is that the reaction time is short compared to start-of-pipe treatment. Sulfide precipitation rates and the concentration of sulfide left after the process had run to completion were measured using an online hydrogen sulfide probe to resolve the fast precipitation reaction. Experiments were conducted in anaerobic wastewaters spiked with sulfide, and carried out under different pH conditions and with various iron-to-sulfide ratios. Sulfide precipitation rates were demonstrated to be faster with Fe(III) than with Fe(II). Experiments furthermore showed that for Fe(III), pH was the controlling parameter, whereas for Fe(II) both pH and the iron-to-sulfide ratio were important. Proposed are model equations to predict variables for the rate equations, which can be adopted by practitioners dealing with sulfide abatement.

Mixtures of straight and defect-free multiwalled carbon nanotubes (MWCNTs), single walled carbon nanohorns (SWCNHs), and multiwalled carbon nanohorns (MWCNHs) were prepared by the arc discharge method. Functionalized Carbon Nanotubes (FCNTs) composed of MWCNTs, MWCNHS and SWCNHs were obtained using acid functionalization process. TiO2/FCNTs (CTP) nanohybrid photocatalysts were obtained with different amounts of FCNTs (2-20 wt%), by wet impregnation method. The photocatalytic activity of both pristine TiO2 as well as the nanohybrids were studied in aqueous glycerol solution under solar irradiation. Reaction parameters such as amount of catalyst and amount of FCNTs in nanohybrids were optimized to ensure high rates of H2 production. With a relatively low amount of pristine TiO2, a high rate of H2 production of 2134 ?mol h-1 gcat -1 has been obtained and is likely due to several factors such as well dispersed catalyst, reduced particle-particle agglomeration, resulting in enhanced light absorption (less light shielding), improved separation of charge carriers and utilization for red-ox reactions. Even better results were obtained with the use of nanohybrid catalysts. The enhanced photocatalytic activities of the nanohybrid catalysts are ascribed to the synergetic effects of FCNTs that minimize light reflection which promotes enhanced solar light sensitization, good dispersion of the catalysts in the reaction solution, and improved surface-interface reactions of photogenerated charge carriers. In the present study 10 wt% FCNTs in nanohybrid (CTP-10) exhibited superior photocatalytic activity for H2 generation, nearly 3 times higher than that of pristine TiO2 catalyst. The CTP-10 photocatalyst exhibited photostability under the experimental conditions studied. The nanohybrid photocatalysts were characterized in order to confirm the crystal structure, morphology, surface chemical composition and optical properties. The present work demonstrates the unique beneficial photocatalytic properties of carbon nanotubes and nanohorn mixtures in nanohybrid photocatalysts, for enhanced H2 production. � 2014 Hydrogen Energy Publications, LLC.

Heat extraction by cold water circulation disturbs the thermo-chemical equilibrium of a geothermal reservoir, activating the dissolution/precipitation of minerals in the fractures. Calcite being a more reactive mineral than other rock minerals composing the earth curst, we investigate the permeability alteration during geothermal heat production from carbonate reservoirs. In this study the simulations are performed using the code FEHM with coupled thermo-hydro-chemical (THC) capabilities for a three dimensional domain. The computational domain consists of a single fracture connecting the injection and production wells. For reactive alteration of aperture, the model considers that the kinetics of dissolution/precipitation is coupled to the equilibrium interactions among the aqueous species/ions. The reaction rate predominantly depends on the temperature dependent solubility and advective-dispersive solute transport in the fracture. Due to the nonuniform flow fields resulting from injection and production, the coupled thermo-hydro-chemical processes initiate significant variation of the aperture alteration rate over the fracture. We have considered different operating conditions such as different mass injection rate, injection temperature and concentration of minerals. Our simulations show that dissolution and precipitation can occur simultaneously at different locations in fracture. Furthermore the reaction rate varies with time and the reaction rate can also switch between dissolution and precipitation. To illustrate this interesting behavior, the variations of shape and size of zero reaction rate contours with time are shown. An interesting outcome is a non-monotonic evolution of the overall transmissivity between the wells. The alteration of overall transmissivity largely depends on the concentration of mineral in the injected water with respect to the solubility at the initial fracture temperature. For both dissolution and precipitation controlled cases, the rapid changes in transmissivity provide challenges for maintaining circulation of water at constant mass flow rate. � 2013 Elsevier Ltd.

A review of the literature about calculating the adsorption properties of arsenic onto mineral models using density functional theory (DFT) is presented. Furthermore, this work presents DFT results that show the effect of model charge, hydration, oxidation state, and DFT method on the structures and adsorption energies for AsIII and AsV onto Fe3+-(oxyhydr)oxide cluster models. Calculated interatomic distances from periodic planewave and cluster-model DFT are compared with experimental data for AsIII and AsV adsorbed to Fe3+-(oxyhydr)oxide models. In addition, reaction rates for the adsorption of AsV on α-FeOOH (goethite) (010) and Fe3+ (oxyhydr)oxide cluster models were calculated using planewave and cluster-model DFT methods.

Investigations of structure and reaction zones of unconfined methane-hydrogen laminar jet diffusion flames are presented. In a lab-scale burner, experiments have been conducted using a mixture of pure methane and pure hydrogen in different volumetric proportions. Digital photographs of the flames have been captured and the radial temperature profiles at different axial locations outside the flame zone have been measured. Numerical simulations are carried out with a C2 chemical kinetics mechanism having 25 species and 121 reaction steps and an optically thin radiation sub-model. The numerical results are validated against the experimental data. Parametric studies have been carried out for a range of methane-hydrogen mixtures with volumetric proportion of hydrogen in the mixture varying from 0% to 80%. Variation of flame height, contours of temperature, mass fractions of product species and the net reaction rates of methane and hydrogen for various cases are presented and discussed in detail. Further, analysis of net reaction rates of important reactions involving methane and hydrogen with radicals such as O, H and OH are analyzed. The maximum temperature in the domain is seen to decrease for the fuel mixtures with higher hydrogen content. The overall flame length also decreases. For a fuel mixture having 40% hydrogen by volume, the net molar consumption rates of methane and hydrogen are found to be almost equal. Examination of individual reactions of fuel species with radicals shows that hydrogen is mainly consumed by its reaction with OH, whereas methane consumption is mainly through its reactions involving H as well as OH radicals. � 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Recognition and binding of specific sites on DNA by proteins is central for many cellular functions such as transcription, replication, and recombination. In the search for its target site, the DNA-associated protein is facing both thermodynamic and kinetic difficulties. The thermodynamic challenge lies in recognizing and tightly binding a cognate (specific) site among the billions of other (non-specific) sequences on the DNA. The kinetic difficulty lies in finding a cognate site in mere seconds amidst the crowded cellular environment that is filled with other DNA sequences and proteins. In this minireview, we will discuss the history of the DNA search problem, the theoretical background and the various experimental methods used to study the kinetics of proteins searching for target sites on DNA.

A series of x wt.% Pt/CeO2 catalysts (x = 0.1-2.0) was prepared to investigate for the first time the effect of Pt particle size on important kinetic and mechanistic aspects of the water-gas shift (WGS) reaction, namely the concentration (μmol g-1) and chemical structure of active adsorbed reaction intermediates present in the "carbon-path" and "hydrogen-path" of the WGS reaction at 300 °C. For this, steady-state isotopic transient kinetic analysis (SSITKA) coupled with in situ DRIFTS and mass spectrometry experiments was performed using D2O and 13CO. α novel transient isotopic experiment performed allowed to quantify the initial transient rates of reactions of adsorbed formate (-COOH) and CO by water, based on which it was concluded that formate should not be considered as an important intermediate. According to the present work, it is proposed that the WGS reaction on ceria-supported Pt at 300 °C occurs largely via the "redox" mechanism, and to a lesser extent via the "associative formate with -OH group regeneration" mechanism. The TOF (s-1) of WGS was found to vary only slightly with Pt particle size (1.3-8.0 nm), while the specific reaction rate based on the length of periphery of Pt-CeO2 interface (μmol cm-1 s-1) was found to significantly increase with increasing platinum loading and mean particle size in the 250-300 °C range. © 2011 Elsevier Inc. All rights reserved. 279 2 287 300 Cited By :110

Fresh sardines were initially exposed to 0, 5 and 10 °C for 24 h and then, stored at either 4 or 8 °C for 12 and 5 d, respectively. The pH, total volatile basic nitrogen (TVBN), oxidation levels and putrescine, cadaverine and histamine concentration were measured. TVBN and histamine formation rates were calculated for the different storage conditions. Samples initially exposed to higher temperatures exhibited a faster development of TVBN and biogenic amines in both 4 and 8 °C storage temperatures. The initial handling temperature is a determining factor for the safety and quality of sardine.

Numerical investigation of laminar counterflow premixed methane-hydrogen-air flames at a low strain rate is presented. Simulations are carried out with a numerical model incorporated with C2 chemical mechanism having 25 species and 121 reaction steps, and with an optically thin radiation submodel. The numerical model is validated using the experimental data reported in the literature in terms of temperature and species concentrations in flames from opposed flow premixed methane-air and hydrogen-air streams. Parametric studies are performed for opposed flowing methanehydrogen and air mixtures. A premixed methane-hydrogen and air with a rich mixture equivalence ratio (1.75) flows from the top duct, and one having a lean mixture equivalence ratio (0.25) flows from the bottom duct. The volumetric fraction of hydrogen in the fuel mixture has been varied from 20 to 80%. The strain rate used in the present study is kept constant at 50 s -1. Variation of velocity, temperature, species concentrations, and net reaction rates of oxygen, methane and hydrogen along the axis for various cases are presented and discussed in detail. Double flame zones are observed for all the cases. The addition of hydrogen to the rich side stream is seen to be effective in modifying the extents of both reaction zones. The reaction rate of methane is seen to be enhanced with the addition of hydrogen. � 2011 by Begell House, Inc.

A variety of aromatic, aliphatic and conjugated alcohols were transformed into the corresponding carboxylic acids and ketones with aq 70% t-BuOOH in the presence of catalytic amounts of bismuth(III) oxide. This method possesses a wide range of capabilities, does not involve cumbersome work-up, exhibits chemoselectivity and proceeds under ambient conditions. The resulting products are obtained in good yields within reasonable time. The overall method is green. � 2010 Georg Thieme Verlag Stuttgart New York.

A jacketed stirred-cell reactor, operated semicontinuously, was used to assess the kinetics of fast ozonation reactions by reactive absorption. The method was applied to the direct ozone reaction with resorcinol. A high resorcinol concentration was used to reach a steady state and to neglect byproduct accumulation. Thus, the mass-transfer rate and, consecutively, the reaction rate were deduced from the ozone mass balance in the gas phase. The gas- and liquid-phase mass-transfer coefficients were previously measured directly through ozone absorption under appropriate conditions. The results emphasized the high sensitivity of the reaction rate constant to the ozone physicochemical properties, especially its solubility, which is controversial in the literature. Therefore, several correlations used to calculate the ozone solubility in water were considered to calculate the second-order reaction rate constant, which varied from 3.57–4.68 × 105 L mol–1 s–1 at 20 °C to 9.50–12.2 × 105 L mol–1 s–1 at 35 °C. The a...

Eyring theory employs the statistical mechanical theory of absolute reaction rates to analyse the transport mechanisms in fluids. A physicochemical methodology combining molecular dynamics (MD) and Eyring theory of reaction rates is proposed for investigating the liquid slip on a solid wall in the nanoscale domain. The method involves the determination of activation energy required for the flow process directly from the MD trajectory information and then calculate the important transport properties of the confined fluid from the activation energy. In order to demonstrate the universal applicability of the proposed methodology in nanofluidics, the slip flow behavior of argon, water and ionic liquid confined in various nanostructures has been investigated. The slip length is found to be size dependent in all the cases. The novelty of this method is that the variations in slip length are explained on the basis of molecular interactions and the subsequent changes in the activation energy. Graphical abstract: [Figure not available: see fulltext.] � 2015, EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.

Photochemical vapor generation of both inorganic and methylmercury species can be achieved with equal efficiency when a sample reaction medium containing 2-10% formic acid is irradiated by low power (0.3 mW) deep UV LED sources with output in the range 245-260 nm. Whereas pseudo first order kinetics is evident for reduction of methylmercury, inorganic mercury does not conform to either first or second order models and the overall reaction rate is proportional to the concentration of formic acid but independent of that of mercury. Noteworthy, is that at room temperature, no reduction of either mercury species is achieved when radiation from 360 nm LEDs is used. A thermal reduction system operating at nominally 85 °C can also be used to reduce both mercury species in a 2% formic acid medium with the initial stages of the reaction being dominated by a first order kinetic process that is approximately 7-fold slower for methylmercury. Despite this disparity in reaction rates, direct speciation is not possible. Using a 10 cm quartz tube cell for cold vapor AAS measurement, a limit of detection of 0.68 ng absolute was achieved for mercury using a 9 min irradiation time with the deep UV LED sources. Precision of replicate measurement was 2.4% RSD for a sampled volume of 480 μl of a 200 ng ml -1 solution of Hg2+ (96 ng absolute) in 2% formic acid. The efficacy of the low power deep UV LED photoreactor was demonstrated by quantitation of total mercury in certified reference materials PACS-2 (marine sediment) and DOLT-4 (fish liver tissue) using the method of additions to compensate for matrix interferences. © The Royal Society of Chemistry 2013.

The present work is focused on the sol-gel synthesis, characterization and catalytic performance evaluation of novel Mg-Ce-Zr-O-based mixed oxides supported Rh catalysts for the purification of H 2-rich gas streams from phenol through steam reforming in the 575-730°C range. Phenol is used as a model compound of tars, the former being one of the main constituents of tars formed during steam gasification and pyrolysis of biomass. Novel Rh catalysts (0.1wt%) supported on Mg-Ce-Zr-O-based mixed oxides modified by alkaline-earth, rare earth, and transition metal ions, having the general formula Mg-Ce-Zr-X-O (where X stands for La, Sr, Ba, Ca and Zn) were systematically studied. The physicochemical properties of the catalysts were evaluated using complementary bulk and surface characterization techniques, such as BET, XPS, in situ XRD, TEM/SAED and SEM/EDX. Transient techniques including H 2-TPR, TPD-CO 2 and TPD-NH 3 were employed in order to characterize redox behavior, surface basicity, and surface acidity of support, respectively. Among the catalysts examined, a 0.1wt% Rh/40Mg-20Ce-20Zr-20La-O was found to exhibit the highest hydrogen product yield, specific H 2 production rate (μmol/m 2min), and the lowest CO/CO 2 product ratio (575-730°C), even when compared to a Ni-based commercial steam reforming of tars catalyst. At 655°C, a H 2 yield of ∼95% and a specific reaction rate of 100μmolH 2/m 2min were obtained for a feed containing 0.5vol% phenol and 40vol% H 2O at a gas hourly space velocity of ∼80,000h -1. This activity behavior is correlated with the largest concentration of basic sites and labile oxygen species (μmol/m 2), and also with the largest acid/base site ratio present in the 40Mg-20Ce-20Zr-20La-O support composition. Steam was also found to be an efficient reagent for the removal of carbonaceous deposits (e.g., C xH y) formed on the catalyst surface during phenol steam reforming. The H/C atom compositional ratio of the carbonaceous deposits was found to depend on reaction temperature. © 2011 Elsevier B.V. 111-112 360 375 Cited By :23

The steam reforming of phenol in the low-temperature range of 350-550°C was studied over 0.5wt% Rh supported on Ce 0.15Zr 0.85O 2, Zr 0.93La 0.07O 2, and Ce 0.13Zr 0.83La 0.04O 2 mixed metal oxides. The reforming specific activity (per gram of catalyst basis) was found to depend on (a) Rh dispersion, (b) the concentration (μmolg -1) of labile oxygen species of support, as determined by " oxygen storage capacity" measurements, and (c) the promotion of the water-gas shift (WGS) reaction rate, all of which largely influenced by the support chemical composition. The addition of 4atom% La 3+ into the Ce 0.15Zr 0.85O 2 crystal structure was found to largely promote the dispersion of Rh, to increase significantly (by a factor of 1.75) the concentration of surface basic sites (μmolm -2) of Ce 0.13Zr 0.83La 0.04O 2 compared to Ce 0.15Zr 0.85O 2 support, to prevent to a large extent the inhibiting role of hydrogen in the rate of WGS reaction, and to influence significantly the concentration and structure of surface reaction intermediates of the WGS, namely: formate (HCOO-) and -OH groups formed on the support, and adsorbed CO formed on the Rh metal. The 0.5wt% Rh/Ce 0.13Zr 0.83La 0.04O 2 catalyst led to a significantly better performance towards steam reforming of phenol in terms of phenol conversion, H 2-yield, and CO/CO 2 product ratio in the 350-450°C range compared to a commercial Ni-based catalyst (44wt% Ni) used for steam reforming reactions. At 400°C, the 0.5wt% Rh/Ce 0.13Zr 0.83La 0.04O 2 catalyst exhibited approximately 54% and 50%, respectively, higher phenol conversion and hydrogen yield, compared to the Ni-based industrial catalyst. The significantly lower CO/CO 2 product ratio obtained in the case of Rh/Ce 0.13Zr 0.83La 0.04O 2 compared to that obtained in the other supported-Rh catalysts is in agreement with the higher kinetic rate for the WGS reaction observed in the former catalyst. © 2012 Elsevier B.V. 117-118 81 95 Cited By :21

Methyl parathion (O,O-dimethyl-O-4-nitrophenyl phosphorothioate) and dichlorvos (2,2-dichlorovinyl-O-O-dimethyl phosphate) are the most commonly used pesticides in India. These pesticides are often found in many surface and groundwater sources and their concentration levels often exceed the drinking water permissible limits recommended by Indian and European drinking water standards. In this study, doping of nitrogen on TiO 2 was carried out with different nitrogen containing organic compounds such as triethylamine, urea, ethylamine and ammonium hydroxide. Nitrogen (N) doped TiO 2 from triethylamine precursor showed better photocatalytic activity under visible and solar radiation for the degradation of methyl parathion and dichlorvos. Studies for the photodegradation of analytical and commercial grade methyl parathion and dichlorvos were carried out with N-doped TiO 2 and Degussa P-25 TiO 2 under UV, visible and solar radiation using batch reactor. N doped TiO 2 showed higher photocatalytic activity under solar radiation compared to UV and visible light. GC-MS analysis of commercial grade methyl parathion showed intermediates such as para-nitrophenol and O,O-dimethyl phosphonic ester in the middle of the photodegradation process. Similarly, commercial grade dichlorvos showed intermediates such as 2,2-dichlorvinyl-O-methyl phosphate and O,O,O-trimethyl phosphonic ester during the reaction. However, at the end of the reaction none of the intermediates were present in the system. Photodegradation of mixed pesticides showed that methyl parathion and dichlorvos were degrading simultaneously. However, the rates of reaction were different from single pesticide degradation. � 2011 Elsevier B.V.

In the present study, hexavalent chromium (Cr(VI)) reduction potential of chromium reductase associated with the cell-free extracts (CFE) of Arthrobacter rhombi-RE species was evaluated. Arthrobacter rhombi-RE, an efficient Cr(VI) reducing bacterium, was enriched and isolated from a chromium-contaminated site. Chromium reductase activity of Arthrobacter rhombi-RE strain was associated with the cell-free extract and the contribution of extracellular enzymes to Cr(VI) reduction was negligible. NADH enhanced the chromium reductase activity. The enzyme activity was optimal at a pH of 5.5 and a temperature of 30 degrees C. Among the ten electron donors screened, sodium pyruvate was the most effective one followed by NADH and propionic acid. Michaelis-Menten constant, K(m), and maximum reaction rate, V(max), obtained from the Lineweaver-Burk plot were 48 microM and 4.09 nM/mg protein/min, respectively, in presence of NADH as electron donor and 170.5 microM and 4.29 nM/mg protein/min, respectively, in presence of sodium pyruvate as electron donor. Ca(2+) enhanced the enzyme activity while Hg(2+), Cd(2+), Ba(2+), and Zn(2+) inhibited the enzyme activity. Among the various immobilization matrices screened, calcium alginate beads seemed to be the most effective one. Though immobilized enzyme system was able to reduce Cr(VI), the performance was not very encouraging in continuous mode of operation.

International audience; In this work, the kinetics of carbonyl sulfide (COS) absorption in a hybrid solvent containing diethanolamine (DBA) dissolved in methanol was studied. The amine concentrations and temperatures ranged from 380 to 2030 mol m-3 and from 298 to 323 K, respectively. With the purpose of estimating reaction rate constants for the COS-DBA system, the rigorous modeling of COS absorption was carried out based on the two-step zwitterion mechanism, used until now in the modeling of the absorption of carbon dioxide and sulfur compounds by alkanolamine aqueous solutions. A downhill simplex optimization method was developed to determine the reaction rate constants, and simultaneously an iterative procedure was followed to estimate the enhancement factor of the COS absorption. As the results show, these optimization procedures led successfully to the appropriate fitting between the experimental and modeled data and also confirm the two-step zwitterion mechanism for this absorption system.

In this work, a detailed first principle study of the mechanism of the heterogeneous catalytic water-gas shift (WGS) reaction on a rhodium cluster is presented. A large number of possible reaction mechanisms relevant to the WGS reaction are explored, and as many as 34 possible pathways are located due to the unsaturated nature of the metal cluster and the multitude of intermediate species binding configurations. Brønsted-Evans-Polanyi relationships and the Sabatier principle are used to locate the kinetic and thermodynamic paths occurring on the rhodium cluster. A detailed potential energy diagram of the kinetically favored mechanism is presented that shows that the RDS of the reaction are the water dissociation, formate association and formate decomposition elementary reactions, with free energy barriers (ΔG‡) of 24.2, 25.9, and 27.0 kcal/mol, respectively. The poisoning effect of coadsorbed CO and the beneficial effect of preadsorbed water on the kinetic rate of this reaction is demonstrated and a water-mediated mechanism is proposed. In the watermediated mechanism favorable H-bonding interactions stabilize Zundel-cations adsorbed to the metal cluster, which manifest a lower energy path for the dissociation of water. Participation of coadsorbed water in this mechanism explains the promoting effect water vapor pressure has on the reaction kinetics (positive reaction order with respect to water) by lowering the free energy of the rate-determining step barrier by 4.0 kcal/mol and causing a 10-fold increase of the reaction rate for the water dissociation elementary reaction step. In addition a presumable preadsorbed water-mediated mechanism is shown to have an even lower free energy barrier (16,9 kcal/mol) causing a 2000-fold increase of the elementary reaction rate for water dissociation. It is suggested that operation of heterogeneous WGS catalysts in a cyclic fashion where water is first preadsorbed might enhance current catalyst performance and CO conversion turnover frequencies. © 2008 American Chemical Society. 112 48 19030 19039 Cited By :23

The mechanism of surface coating formation (the so-called surface altered layers [SALs] or leached layers) during weathering of silicate minerals is controversial and hinges on understanding the saturation state of the fluid at the dissolving mineral surface. Here we present in-situ data on the evolution of the interfacial fluid composition during dissolution of wollastonite (CaSiO3), obtained using interferometry and micro pH and ion-selective electrodes. Steep concentration gradients develop at the mineral interface as soon as it makes contact with the solution. This interfacial fluid becomes supersaturated with respect to amorphous silica that forms a surface coating, limiting fluid access to the mineral surface and hence affecting the dissolution rate. The thickness of the supersaturated zone and the precipitated layer depends on the relative rates of mass transport and surface reaction in the system; this effect could contribute to the discrepancy between dissolution rates measured in the field and in the laboratory. As well, our results have implications for predictions of silicate weathering rates and hence climate evolution, as different assumptions on dissolution mechanisms affect calculations on CO2 drawdown during weathering and consequent effects on estimates of global mean temperatures.

The kinetics of cellulose hydrolysis by commercially available Cellubrix were described mathematically, with Avicel and wheat straw as substrates. It was demonstrated that hydrolysis could be described by three reactions: direct glucose formation and indirect glucose formation via cellobiose. Hydrolysis did not involve any soluble oligomers apart from low amounts of cellobiose. Phenomena included in the mathematical model were substrate limitation, adsorption of enzyme onto substrate, glucose inhibition, temperature dependency of reaction rates, and thermal enzyme inactivation. In addition, substrate heterogeneity was described by a recalcitrance constant. Model parameters refer to both enzyme characteristics and substrate-specific characteristics. Quantitative model development was carried out on the basis of Avicel hydrolysis. In order to describe wheat straw hydrolysis, wheat straw specific parameter values were measured. Updating the pertinent parameters for wheat straw yielded a satisfactory description of wheat straw hydrolysis, thus underlining the generic potential of the model. Chemicals / CAS: cellobiose, 16462-44-5, 528-50-7; cellulose, 61991-22-8, 68073-05-2, 9004-34-6; glucose, 50-99-7, 84778-64-3; microcrystalline cellulose, 39394-43-9, 51395-75-6

Tungsten trioxide nanorods have been generated by the thermal decomposition (450 °C) of tetrabutylammonium decatungstate. The synthesized tungsten trioxide (WO3) nanorods have been characterized by XRD, Raman, SEM, TEM, HRTEM and cyclic voltammetry. High resolution transmission electron microscopy and X-ray diffraction analysis showed that the synthesized WO3nanorods are crystalline in nature with monoclinic structure. The electrochemical experiments showed that they constitute a better electrocatalytic system for hydrogen evolution reaction in acid medium compared to their bulk counterpart.

International audience; Petroleum cokes are widely used in cement plants for energy generation. Because of their very low volatile content, the physicochemical processes occurring during their combustion should be mainly controlled by heterogeneous reactions. The reactivities of some petroleum cokes toward NO between 800 and 1000 °C have been characterized through experiments in an entrained flow reactor. These carbonaceous materials exhibit very high reactivities toward NO. Their capacity to reduce NO concentration in the surrounding gas is significant, so that this reaction can have a significant impact in terms of NO emissions resulting from their combustion. The influence of surface area and of the heavy metal content on surface reactivity was tested. As it was the case for carbon−oxygen reaction, the surface measured by mercury porosimetry seems to be a good parameter to calculate surface reaction rate. No correlation was found between calcium or iron content and NO−carbon reaction rate. As for the reaction of petroleum coke with oxygen, vanadium appears to have a catalytic effect on the reduction reaction of NO with carbon.

[EN] Three MIL-100 (Fe) samples differing in average crystal size (from 60-70 to >400 nm) have been synthesized by microwave heating using three HF/Fe 3+ ratios. Oxidation of diphenylmethane with tert-butylhydroperoxide (TBHP) and thiophenol with oxygen are catalyzed by three MIL-100 (Fe) samples with similar reaction rates regardless of its average particle size. In contrast, the activity of the three MIL-100 (Fe) samples for the oxidation of bulky triphenylmethane by TBHP largely depends on the average crystal size of the sample: the smaller the average particle size, the larger the initial reaction rate of triphenylmethane oxidation. These results show that diffusion limitation takes place on MOF catalysis depending on the substrate size and provides indirect evidence that these reactions take place inside the intracrystalline space of the porous catalysts. © 2011 The Royal Society of Chemistry., Financial support by the Spanish DGI (CTQ2009-11587 and CTQ2010-18671 and Consolider MULTICAT) is gratefully acknowledged. Prof. Jong-San Chang and his group are thanked for providing us with sufficient quantities of the three MIL-100 (Fe) samples. Korean researchers acknowledge the financial support of KICOS and KRICT for the international collaboration program.