Kinetics of hematite chlorination with Cl2 and Cl2 + O2: Part I. Chlorination with Cl2

Preliminary tests of the chlorination of two iron oxides (wüstite and hematite) in various chlorinating gas mixtures were performed by thermogravimetric analysis (TGA) under non-isothermal conditions. Wüstite started to react with chlorine from about 200 °C generating ferric chloride and hematite as the final reaction products. The presence of a reducing and oxidizing agent in the chlorinating gas mixtures influenced the chlorination reactions of both iron oxides, during non-isothermal treatment, only at temperatures higher than 500 °C.The chlorination kinetics of hematite with Cl₂ have been studied in details between 600 and 1025 °C under isothermal chlorination. The values of the apparent activation energy (E_a) were about 180 and 75 kJ/mol in the temperature ranges of 600–875 and 875–1025 °C, respectively. The apparent reaction order with respect to Cl₂ was found to be 0.67 at 750 °C. Mathematical model fitting of the kinetics data was carried out to determine the most probable reaction mechanisms.     

Unveiling the crucial role of temperature on the stability of oxygen reduction reaction electrocatalysts

The stability of Pt-based/C electrocatalysts used in proton exchange membrane fuel cell (PEMFC) systems is commonly evaluated via accelerated stress testing in half-cell configuration at temperature close to ambient (20 ≤ T ≤ 25 °C), and 100% relative humidity (liquid electrolyte). Those conditions are by far different from those encountered in PEMFC systems (solid electrolyte, 60 ≤ T ≤ 80 °C, 0 ≤ relative humidity ≤ 100%), and fail in reproducing the morphological changes and the performance losses encountered during real life. Here, using a high surface area Pt/C electrocatalyst, we show that the gap between half-cell and real PEMFC configurations can be bridged by considering the pronounced effect of the temperature. The accelerated stress tests (ASTs) conducted in liquid electrolyte at T = 80 °C more accurately reflect the changes in morphology and surface reactivity occurring in real PEMFC environment, and provide gain in time. Due to massive release of Pt^z + ions in the electrolyte during ASTs performed at T = 80 °C, using fresh electrolyte is strongly recommended for correct determination of the oxygen reduction reaction (ORR) kinetics.     

Lipase catalyzed enantioselective desymmetrization of a prochiral pentane-1,3,5-triol derivative

The enantioselective desymmetrization of the prochiral 3-O-silyl protected pentanetriol derivative 3 was carefully investigated. At −10 °C, the bacterial lipase from Burkholderia cepacia immobilized on ceramic particles led to monoacetate (S)-4 in 52% yield and >99.9% ee. At a reaction temperature of −40 °C the yield and enantioselectivity were even higher, but the reaction time was very long. Theoretical simulations of the reaction progress indicated an enantioselectivity of 25:1 at −10 °C and 35:1 at −40 °C. (S)-4 was converted into the enantiomerically pure building block 5-azidopentane-1,3-diol (S)-7 in two steps. The absolute configuration of (S)-7 was determined by exciton-coupled circular dichroism (ECCD) of diester (S)-8.     

High oxygen-reduction activity of silk-derived activated carbon

Activated carbon prepared from silk fibroin, which is free of metal elements, showed a high catalytic activity for the oxygen-reduction reaction (ORR). The activated carbon had a very high onset potential of E_onset = 0.83 V (vs. RHE) in oxygen-saturated 0.5 M H₂SO₄ at 60 °C. The ORR on the activated carbon proceeded by a four-electron process in the high-electrode-potential region; this gradually decreased to a 3.5-electron reaction below about 0.6 V (vs. RHE). Only about 1% of nitrogen atoms (mostly quaternary) remained in the activated carbon by heat-treatment at up to 1200 °C are responsible for the high catalytic activity. The open circuit voltage of a polymer electrolyte fuel cell using the activated carbon as the cathode and a platinum/carbon black anode under pure oxygen and hydrogen gases, respectively, both at one atmosphere, was 0.96 V at 27 °C.     

Kinetic study of nucleophilic reactivity of heterocyclic amines with 4,6-dinitrobenzofuroxan in acetonitrile

The reaction kinetics of 4,6-dinitrobenzofuroxan with five heterocyclic amines was investigated spectrophotometrically (UV–Vis) in acetonitrile at 20 °C. It was observed that the rate constants of these reactions increased as follows: 2-aminopyrimidine > 2-aminothiazole > 2-aminobenzothiazole > 5-amino-3,4-dimethylisoxazole > 2-amino-5-trifluoromethyl-1,3,4-thiadiazole. Further, second-order rate constants (k₁) pertaining to the C–N and C–C bond forming step of these complexation processes fit to the three parameter equation log k (20 °C) = s_N (N + E), allowing the determination of the nucleophilicity parameters (N) of the five heterocyclic amines. The heterocyclic amines were subsequently ranked on the comprehensive nucleophilicity scale defined by Mayr et al. (2003), providing a direct comparison of n-, π-, and σ-nucleophiles.     

The electrochemical properties of thermophilic cytochrome P450 CYP119A2 at extremely high temperatures in poly(ethylene oxide)

The electrochemical measurements were carried out by using thermophilic cytochrome P450 CYP119A2 (P450st) modified with poly(ethylene oxide) (PEO) in PEO₂₀₀ as an electrochemical solvent. The PEO modified P450st gave clear reduction–oxidation peaks by cyclic voltammetry in oxygen-free PEO₂₀₀ up to 120 °C. The midpoint potential measured for the P450st was −120 mV vs. [Fe(CN)₆]⁴⁻/[Fe(CN)₆]³⁻ at 120 °C. The peak separation, ΔE, was 16 mV at 100 mV/s. The estimated electron transfer rate of PEO-P450st at 120 °C was 35.1 s⁻¹. The faster electron transfer reaction was achieved at higher temperatures. The electrochemical reduction of dioxygen was observed at 115 °C with the PEO-modified P450st system.     

Molecular characterization of Ulex europaeus biochar obtained from laboratory heat treatment experiments – A pyrolysis–GC/MS study

Gorse species (Ulex sp.) are ubiquitous in the shrublands of NW Spain and have the potential to become key players in an integral biofuel/biochar program in NW Spain. Here we present molecular characterization (using pyrolysis–GC/MS) of a biochar “thermosequence” obtained by laboratory heating of Ulex europaeus wood in a muffle furnace between 200 and 600 °C (T_CHAR). Low temperature chars (T_CHAR ≤ 350 °C) produced significant amounts of pyrolysis products of which the precursor biopolymer could be recognized, while high-temperature chars (T_CHAR ≥ 400 °C) produced mainly phenols and monocyclic and polycyclic aromatic hydrocarbons, which are not specific for any biopolymer. Carbohydrate could hardly be recognized at T_CHAR ≥ 350 °C. The thermal rearrangement of polyphenols, mainly lignin, was reflected in more detail (1) C₃-side chain shortening and probably depolymerization (T_CHAR 200–350 °C), (2) demethoxylation of syringyl and probably also some guaiacyl lignin (T_CHAR 300–400 °C), (3) elimination of virtually all remaining methoxyl groups (T_CHAR 350–400 °C), through dehydroxylation and demethoxylation, (4) almost complete dehydroxylation of lignin and other biopolymers (T_CHAR 400–500 °C), (5) progressive condensation into polyaromatic structures (T_CHAR 300–500 °C) and (6) partial elimination of alkyl bridges between (poly)aromatic moieties (T_CHAR 450–500 °C). These results were supported by Fourier transform infrared spectroscopy (FTIR) of the same samples. We conclude that pyrolysis–GC/MS can be used as a rapid molecular screening method of gorse-derived biochar. Molecular properties elucidation is an essential part of predicting the stability and agronomical behavior of gorse-derived biochar after future implementation in soils.     

Development of novel reactions using ruthenium carbene catalyst and its application to novel methods for preparing nitrogen-containing heterocycles

The reaction of N-allyl-ortho-vinylaniline with ruthenium carbene catalyst at 50 °C gives substituted 1,2-dihydroquinoline through ring-closing metathesis (RCM), which is easily converted to the corresponding quinoline after deprotection. In sharp contrast, when vinyloxytrimethylsilane is added to this reaction mixture, 1,2-dihydroquinoline is not formed and selective isomerization of N-allyl-ortho-vinylaniline is observed at 50 °C to give corresponding enamide, which is successfully converted to indole derivative by RCM. The same catalyst system provide indoline derivative at 160 °C by cycloisomerization. Based on a detailed mechanistic study, it becomes clear that a ruthenium carbene catalyst, which is highly effective for RCM, reacts with an electron-rich terminal olefin selectively, and another ruthenium species, which effectively catalyzes the isomerization of terminal olefin and cycloisomerization of alpha, omega-diene, is generated.     

Effects of calcination and activation temperature on dry reforming catalysts

The effect of calcination temperatures on dry reforming catalysts supported on high surface area alumina Ni/γ-Al₂O₃ (SA-6175) was studied experimentally. In this study, the prepared catalyst was tested in a micro tubular reactor using temperature ranges of 500, 600, 700 and 800 °C at atmospheric pressure, using a total flow rate of 33 ml/min consisting of 3 ml/min of N₂, 15 ml/min of CO₂ and 15 ml/min of CH₄. The calcination was carried out in the range of 500–900 °C. The catalyst is activated inside the reactor at 500–800 °C using hydrogen gas. It was observed that calcination enhances catalyst activity which increases as calcination and reaction temperatures were increased. The highest conversion was obtained at 800 °C reaction temperature by using catalyst calcined at 900 °C and activation at 700 °C. The catalyst characterization conducted supported the observed experimental results.     

Synthesis,growth, and characterization of a new NLO material 3-(2,3-dimethoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one

3-(2,3-Dimethoxyphenyl)-1-(pyridin-2-yl)prop-2-en-1-one (DMPP) a potential second harmonic generating (SHG) has been synthesized and grown as a single crystal by the slow evaporation technique at ambient temperature. The structure determination of the grown crystal was done by single crystal X-ray diffraction study. DMPP crystallizes with orthorhombic system with cell parameters a = 20.3106(8) Å, b = 4.9574(2) Å, c = 13.4863(5) Å, α = 90°, β = 90°, γ = 90° and space group Pca2₁. The crystals were characterized by FT-IR, thermal analysis, UV–vis–NIR spectroscopy and SHG measurements. Various functional groups present in DMPP were ascertained by FTIR analysis. DMPP is thermally stable up to 80 °C and optically transparent in the visible region. The crystal exhibits SHG efficiency comparable to that of KDP.     

Electrode properties of Sr doped La2CuO4 as new cathode material for intermediate-temperature SOFCs

High performance La_2−xSr_xCuO_4−δ (x = 0.1, 0.3, 0.5) cathode materials for intermediate temperature solid oxide fuel cell (IT-SOFCs) were prepared and characterized. The investigation of electrical properties indicated that La_1.7Sr_0.3CuO₄ cathode has low area specific resistance (ASR) of 0.16 Ω cm² at 700 °C and 1.2 Ω cm² at 500 °C in air. The rate-limiting step for oxygen reduction reaction on La_1.7Sr_0.3CuO₄ electrode changed with oxygen partial pressure and measurement temperature. La_1.7Sr_0.3CuO₄ cathode exhibits the lowest overpotential of about 100 mV at a current density of 150 mA cm⁻² at 700 °C in air.     

Phase transitions of CaTiO3 ceramics sintered with the aid of NaF and MgF2

New phases with initial composition (1 ? x)CaTiO₃ ? xNaF ? xMgF₂ (0 ≤ x ≤ 0.20) have been prepared at low temperature (950 °C) from mixtures of CaTiO₃ and fluorides NaF and MgF₂. The oxyfluorides obtained have been characterized by X-ray diffraction at room temperature and indexed by isotypy with orthorhombic CaTiO₃. The microstructures of these phases are observed by scanning electron microscopy. Dielectric measurements have been carried out during cooling cycle from 500 °C to room temperature at two frequencies (100 Hz, 1 kHz). Differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermogravimetry (DTG) analyses have been performed, respectively, from room temperature up to 550 °C (DSC) and 920 °C (TG–DTG). The dielectric measurements revealed two anomalies which have been confirmed by DSC analyses. These phenomena are ascribed to second order phase transitions. The variation of the real permittivity with temperature is in agreement with the class I capacitor specifications. However, the dielectric losses have to be improved.     

Synthesis and photovoltaic property of polymer semiconductor with phthalimide derivative as a promising electron withdrawing material

Donor–acceptor type (DA-type) polymeric photovoltaic material with a dicarboxylic imide-substituted benzene (phthalimide) derivative as electron-withdrawing units, poly[4,4′-didodecyl-2,2′-bithiophene-co-5,5′-(3,6-bis(thieno-2-yl)-N-octyl-phthalimide] (PDBTTPT), was synthesized by a Stille coupling reaction. It had an optical band gap of 1.96 V and a relatively low HOMO energy level of ?5.34 eV in spite of it being a thiophene-based polymer. Photovoltaic devices with PDBTTPT/PC₇₁BM active layers were fabricated under a variety of conditions for optimizing device performance. PDBTTPT exhibited the best power conversion efficiency (PCE) of 1.5% in the device where 80 wt.% of the PC₇₁BM was contained in the active layer (PDBTTPT:PC₇₁BM = 1:4, w/w) and which was pre-annealed at 120 °C for 10 min. In addition, a device which was pre-annealed at 140 °C for 10 min and a device which was post-annealed at 120 °C for 10 min showed analogous PCE values of 1.5% as well, although small differences were exhibited between various parameters, such as V_OC, J_SC, and FF.     

Thermal Stability of α-Phycoerythrocyanin

The α-subunit of the phycobiliprotein, phycoerythrocyanin (α-PEC), from Mastigocladus laminosus shows photoreversible photochromism that is based on the Z ↔ E isomerization of the phycoviolobilin (PVB) chromophore. Thermal stability of the photochemistry and chromoprotein secondary structure have been studied by absorption and circular dichroism (CD) spectroscopy. Both photoisomers are stable and photoconvertible up to ∼ 70 °C. At T > 75 °C, photochemistry ceases because the E-state reverts rapidly thermally to the Z–state. The chromoprotein melts at 72 °C, the apoprotein already at 55 °C, indicating a considerable stabilization of the protein secondary structure by the chromophore.     

Nickel(0)/N-heterocyclic carbene complexes catalysed arylation of aromatic diamines

Nickel complexes of N-heterocyclic carbenes were examined for effecting C–N coupling reactions between aromatic diamines and aryl chlorides of varying electron density. The Ni(0) · 2IPr (IPr = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) complex associated to t-BuONa allowed N,N′-diarylation at 100 °C in 1,4-dioxane with excellent yields. Selective monoarylation of diamines could be performed in THF at 65 °C.     

Studies of dielectric characteristics of BaBi2Nb2O9 ferroelectrics prepared by chemical precursor decomposition method

BaBiNb₂O₉ (BBN) powders in the nanometer range were prepared by chemical precursor decomposition method (CPD). TG–DTA showed that precursor sample got freed from organic contaminants at 575 °C. XRD showed that a single phase with the layered perovskite structure of BBN was formed after calcining at 600 °C. No intermediate phase was found during heat treatment at and above 600 °C. The crystallite size (D) and the effective strain (η) were found to be 26 nm and 0.000867, respectively, while the particle size obtained from TEM was 28 ± 2 nm. SEM revealed that the average grain size after sintering at 900 °C for 4 h was ∼1.67 μm. A relative density of ∼93% was obtained using a two-step sintering process at moderate pressure. Dielectric and ferroelectric properties were investigated in the temperature range 50–500 °C and frequencies from 1 kHz to 5 MHz. Strong dispersion of the complex relative dielectric constant was observed including typical relaxor features such as shift of permittivity maximum with frequency and broadening of the peak maximum. The high dielectric constant of 545 measured at 100 kHz and other properties of BBN ceramics were compared to that of BBN prepared by other conventional methods and found to be superior.     

Semivolatile and volatile compounds from the pyrolysis and combustion of polyvinyl chloride

Emissions evolved from the pyrolysis and combustion of polyvinyl chloride (PVC) were studied at four different temperatures (500, 700, 850 and 1000 °C) in a horizontal laboratory tubular quartz reactor in order to analyse the influence of both temperature and reaction atmosphere on the final products from thermal and oxidative reactions. It was observed that the CO₂/CO ratio increased with temperature. Methane was the only light hydrocarbon whose yield increased with temperature up to 1000 °C. Benzene was rather stable at high temperatures, but in general, combustion at temperatures above 500 °C was enough to destroy light hydrocarbons. Semivolatile hydrocarbons were collected in XAD-2 resin and more than 160 compounds were detected. Trends on polyaromatic hydrocarbon (PAH) yields showed that most had a maximum at 850 °C in pyrolysis, but naphthalene at 700 °C. Formation of chlorinated aromatics was detected. A detailed analysis of all isomers of chlorobenzenes and chlorophenols was performed. Both of them reached higher total yields in combustion runs, the first ones having a maximum at 700 °C and the latter at 500 °C. Pyrolysis and combustion runs at 850 °C were conducted to study the formation of polychlorodibenzo-p-dioxins (PCDDs) and polychlorodibenzofurans (PCDFs). There was more than 20-fold increase in total yields from pyrolysis to combustion, and PCDF yields represented in each case about 10 times PCDD yields.     

A new calcium trimellitate coordination polymer with a chain-like structure

The calcium trimellitate, Ca(H₂O)[(O₂C)₂–C₆H₃–CO₂H], was hydrothermally synthesized from a mixture of calcium hydroxide, 1,2,4-benzenetricarboxylic (or trimellitic) acid and water at 180 °C for 24 h (under autogenous pressure). Its crystal structure has been determined by single-crystal X-ray diffraction analysis using synchrotron radiation (station 9.8, SRS Daresbury, UK). It consists of infinite chains of calcium bicapped trigonal prismatic polyhedra connected to each other through the 1,2,4-benzenetricarboxylate ligand. The eight-fold coordinated calcium cation is bonded to one terminal water molecule, two carboxylate groups with a chelating conformation and three carboxylate groups in a monodentating mode. One of the monodentate carboxylate is terminal with the occurrence of protonated C–OH bonding.Triclinic space group P-1 with a = 6.9073(4) Å, b = 6.9917(4) Å, c = 10.3561(6) Å, α = 87.178(1)°, β = 83.233(1)°, γ = 69.576(1)°, V = 465.41(5) Å³.     

Study of immobilized candida rugosa lipase for biodiesel fuel production from palm oil by flow microcalorimetry

Enzymatic transesterification of palm oil with methanol and ethanol was studied. Of the four lipases that were tested in the initial screening, lipase Candida Rugosa (CR) resulted in the highest yield of mono alkyl esters. Lipase CR was further investigated in immobilized form within an activated carbon as support. The activated carbon was prepared by activation physical. Using the immobilized lipase CR, the effects of water and alcohol concentration, enzyme loading and enzyme thermal stability in the transesterification reaction were investigated. The optimal conditions for processing 50 g of palm oil were: 37 °C, 1:14.5 oil/methanol molar ratio, 1.0 g water and 500 mg lipase for the reactions with methanol, 35 °C, 1:15.0 oil/ethanol molar ratio, 1.0 g water, 500 mg lipase for the reactions with ethanol, and 35 °C, 1:10.0 oil/n-butanol molar ratio, 1.0 g water, 500 mg lipase for the reactions with ethanol. Subject to the optimal conditions, methyl and ethyl esters formation of 70 and 85 mol% in 1 h of reaction were obtained for the immobilized enzyme reactions. The flow microcalorimetry is an important and novel techniques is used in evaluation of biodiesel production.     

Syntheses and structures of the MOF-type series of metal 1,4,5,8,-naphthalenetetracarboxylates M2(OH)2[C14O8H4] (Al,Ga, In) with infinite trans-connected M–OH–M chains (MIL-122)

Three new isostructural MOF-type compounds (named MIL-122) have been obtained from the hydrothermal reaction at 210 °C for 24 h of the 1,4,5,8-naphthalenetetracarboxylic acid with aluminum, gallium or indium source in water. The structures of the compounds M₂(OH)₂[C₁₄H₄O₈] (M = Al, Ga, In) have been solved ab initio from powder X-ray diffraction analysis using the synchrotron radiation (Soleil; station CRISTAL). The three-dimensional organic–inorganic framework exhibits infinite straight chains of metal-centered octahedra sharing trans corners linked to each other through the 1,4,5,8-naphthalenetetracarboxylate ligand. The cations Al, Ga or In, are coordinated by four oxygen atoms coming from the carboxyl groups and two bridging hydroxyl groups μ₂-OH, located in trans position in the octahedral surrounding. The compounds characterized by thermogravimetric and thermodiffraction analyses are thermally stable up to 440, 460 and 380 °C, for Al, Ga and In, respectively. Crystal data: monoclinic cell; P2₁/c (n°14); for MIL-122 (Al): a = 9.5174(2), b = 10.0706(1), c = 6.6465(2) Å, β = 91.2614(5)°, V = 636.878(2) Å³, Z = 2; for MIL-122 (Ga): a = 9.6501(1), b = 10.0585(1), c = 6.75069(9) Å, β = 92.4786(9)°, V = 654.65(1) Å³, Z = 2; for MIL-122 (In): a = 9.92359(5), b = 10.19765(7), c = 7.19357(4) Å, β = 727.034(8)°, V = 727.034(8)ų, Z = 2.