Reaction between Hydrosulfide and Iron/cerium (hydr)oxide: Hydrosulfide Oxidation and Iron Dissolution Kinetics

Hydrosulfide oxidation and iron dissolution kinetics were studied at normal pressure, under inert (N₂) atmosphere, in a liquid–solid mechanically-stirred slurry reactor. The kinetic variables undergoing variations were: hydrosulfide initial concentration (0.90–3.30 mmol/L), oxide initial surface area (16–143 m²/L) and pH (8.0–11.0). The hydrosulfide consumption and products (thiosulfate and polysulfide) formation were quantified by means of capillary electrophoresis, while iron dissolution was monitored through atomic absorption spectroscopy. Most of Fe(II) produced at pH = 9.5 remained associated with the oxide surface in the time-scale of the experiments. The hydrosulfide oxidation by the iron/cerium (hydr)oxide was found to be surface-controlled, with rates (R_i) of both sulfide oxidation and Fe(II) dissolution expressed in terms of an empirical rate equation: R_i = k_i[HS⁻]_t=0^−0.5[A]_t=0[H⁺]_t=0^−0.5 , where k_i represents the apparent rate constants for the oxidation of HS⁻ (k_HS) or the dissolution of Fe(II) (k_Fe), [HS⁻]_{t = 0} is the initial hydrosulfide concentration, [A]_{t = 0} is the initial Fe/Ce (hydr)oxide surface area and [H⁺]_{t = 0} is the initial proton concentration. The rate constant, k_HS, for the oxidation of hydrosulfide at pH = 9.5 was (3.4219 ± 0.65) × 10⁻⁴ mol² L⁻¹ m⁻² min⁻¹, with the rate of hydrosulfide oxidation being ca. 10 times faster than the rate of Fe(II) dissolution (assuming a 1:2 stoichiometric ratio between HS⁻ oxidized and Fe(II) produced; k_Fe = (3.9116 ± 0.41) × 10⁻⁵ mol² L⁻¹ m⁻² min⁻¹).     

Kinetic characterization of Prussian Blue-modified graphite electrodes for amperometric detection of hydrogen peroxide

Prussian Blue-modified graphite electrodes (G/PB) with electrocatalytic activity toward H₂O₂ reduction were obtained by PB potentiostatic electrodeposition from a mixture containing 2.5 mm FeCl₃ + 2.5 mm K₃[Fe(CN)₆] + 0.1 m KCl + 0.1 m HCl. From cyclic voltammetric measurements, performed in KCl aqueous solutions of different concentrations (5 × 10⁻²–1 m), the rate constant for the heterogeneous electron transfer (k _s) was estimated by using the Laviron treatment. The highest k_s value (10.7 s⁻¹) was found for 1 m KCl solution. The differences between the electrochemical parameters of the voltammetric response, as well as the shift of the formal potential, observed in the presence of Cl⁻ and NO₃⁻ compared to those observed in the presence of SO₄²⁻ ions, points to the involvement of anions in the redox reactions of PB. The G/PB electrodes showed a good electrochemical stability proved by a low deactivation rate constant (0.8 × 10⁻¹² mol cm² s⁻¹). The electrocatalytic efficiency, estimated as the ratio , was found to be 3.6 (at an applied potential of 0 mV vs. SCE; Γ = 5 × 10⁻⁸ mol cm⁻²) for a H₂O₂ concentration of 5 mm, thus indicating G/PB electrodes as possible H₂O₂ sensors.     

Modeling the aqueous reaction kinetics of estriol with ferrate

In this study the aqueous oxidation kinetics of estriol (E3) by potassium ferrate (K₂FeO₄), a chemical for its strong oxidizing power and for producing a coagulant from its reduced state (i.e. Fe(III)), was evaluated in the range of pH 8–12 with different molar ratios of the reactants. As the degree of Fe(VI) protonation varies with the solution pH, it was found that a first order model was not suitable to describe the oxidation reaction. This paper describes a theoretical representation that closely models the reaction kinetics of E3 and ferrate. From this modeling, the reaction rates of HFeO₄ ⁻ and FeO₄ ²⁻ with E3 have been determined. The results show that the reactivity of HFeO₄ ⁻ with dissociated and undissociated E3 is greater than that of FeO₄ ²⁻, and that E3 is more reactive in its dissociated state.     

Hydrodechlorination of 2,4,6-trichlorophenol for a permeable reactive barrier using zero-valent iron and catalyzed iron

Dehalogenation of toxic organic compounds has been intensively studied during the last decade by using zero-valent iron (ZVI). However, the reactivity of iron is compound specific and very low reactivities were reported for aromatic compounds including chlorophenols. In this study, hydrodechlorination of 2,4,6-trichlorophenol (2,4,6-TCP) was conducted in a batch system by using ZVI and catalyzed iron. No degradation was observed with ZVI over the 40 days experiments. Catalyzed ZVIs removed 2,4,6-TCP and palladium-coated iron (Pd/Fe) and nickel-coated iron (Ni/Fe) showed relatively enhanced reactivity while copper-coated iron (Cu/Fe) and platinum-coated iron (Pt/Fe) showed lower reactivities. The surface area normalized kinetic constants (k _SA ) of Pd/Fe, Ni/Fe, Cu/Fe, Pt/Fe are 2.54×10⁻⁴, 1.01 × 10⁻⁴, 2.24×10⁻⁵, 2.56×10⁻⁵ L m⁻² h⁻¹, respectively. The identification of less chlorinated phenols and phenol confirmed that the removal is dechlorination. Pd/Fe system exerts relatively low pH compared with the ZVI system, and the low pH is favorable for the dechlorination. The reactivity enhancement of catalyzed iron was discussed in terms of catalytic effects and the corrosion potential by the bimetal coupling. Variable Pd content on the Pd/Fe was tested, and the degradation rate of 2,4,6-TCP increased in proportion to the increase of Pd content.     

The catalytic activity of Ni/W bimetallic sulfide nanostructured catalysts in the hydrodesulfurization of dibenzothiophene

Two types of catalysts containing NiW bimetallic sulfide nanostructures were prepared by a chemical method employing ammonium thiotungstate and nickel nitrate as metal-sulfide precursors followed by sulfidation in H₂S/H₂ at 400 °C. The nanostructures were grown with excess of Ni, at atomic ratio R = 0.75, 0.85 (R = Ni/Ni + W). High resolution electron microscopy (HRTEM) micrographs revealed the formation of two types of nanostructures, nickel sulfide nanoparticles and long nanorods of tungsten suboxide, both coated by WS₂ layers. The Ni/W catalyst containing mostly nanorods presented twice the catalytic activity (pseudo-zero order constant rate k = 12 × 10⁻⁷ mol/s.g) of the Ni/W catalyst containing nanoparticles (k = 6.3 × 10⁻⁷ mol/s.g) with a low selectivity for tetrahydrodibenzothiophene (THDBT) and high selectivity to cyclohexylbenzene (CHB, 50 mol%). In turn the Ni/W catalyst containing nanoparticles presented a catalytic activity comparable to a Ni/Mo catalyst without inorganic fullerene (IF) nanostructures (k = 7.2 × 10⁻⁷ mol/s.g) but with higher selectivity for hydrogenation to THDBT, (14 mol%) than the sample with nanorods.     

Kinetics for free radical solution polymerization of heptadecafluorodecyl (meth)acrylate in supercritical carbon dioxide

Free radical solution polymerization of heptadecafluorodecyl acrylate (HDFDA) and heptadecafluorodecyl methacrylate (HDFDMA) was carried out by using 2,2′-azobisisobutyronitrile (AIBN) as the initiator in supercritical carbon dioxide (scCO₂). We performed solution polymerization with changing initiator concentration, temperature and polymerization time to study the polymerization kinetics. A nonlinear least square method and dead-end theory were used to determine the constant, K (K=(k _p √f)/√k _d k _d ) and initiator decomposition rate constant (k _d ) from experimental data. k _d was measured as 3.77 × 10⁻⁵ s⁻¹ at 62.7°C for poly(HDFDA) and 2.71 × 10⁻⁵ s⁻¹ at 62.5 °C for poly(HDFDMA), respectively, by nonlinear least square method.     

Electrochemical properties of Li1?z(Ni1?yFey)1+zO2 synthesized by the combustion method in an air atmosphere

For the syntheses of LiNi_1−y Fe _y O₂ (0.000 ≤ y ≤ 0.300), mixtures of the starting materials with the desired compositions were preheated in an air atmosphere at 400 °C for 30 min and calcined in air at 700 °C for 48 h. The phases appearing in the intermediate reaction steps for the formation of lithium nickel oxide are deduced from the DTA analysis. XRD analysis, FE-SEM observation, FTIR analysis and electrochemical measurement were performed for the synthesized Li_1−z (Ni_1−y Fe _y )_1+z O₂ (0.000 ≤ y ≤ 0.300) samples. The samples of Li_1−z (Ni_1−y Fe _y )_1+z O₂ with y = 0.025 and 0.050 have higher first discharge capacities than Li_1−z (Ni_1−y Fe _y )_1+z O₂ with y = 0.000 and better or similar cycling performance at the 0.1 C rate in the voltage range of 2.7–4.2 V. Similar results have not previously been reported except for Co-substituted LiNiO₂. The sample Li_1−z (Ni_0.975Fe_0.025)_1+z O₂ has the highest first discharge capacity (176.5 mAh g⁻¹). Rietveld refinement of the XRD patterns of LiNi_1−y Fe _y O₂ (0.000 < y ≤ 0.100) from a starting structure model [Li,Ni]_3b[Li,Ni,Fe]_3a[O₂]_6c showed that cation disordering occurred in the samples.     

H/D Exchange on Silica-Grafted Tantalum(V) Imido Amido [(≡SiO)<Subscript>2</Subscript>Ta<Superscript>(V)</Superscript>(NH)(NH<Subscript>2</Subscript>)] Synthesized from Either Ammonia or Dinitrogen: IR and DFT Evidence for Heterolytic Splitting of D<Subscript>2</Subscript>

The silica-grafted Ta^(V) imido amido complex [(≡SiO)₂Ta(NH)(NH₂)], 2, obtained from the reaction of either ammonia or dinitrogen plus hydrogen with the silica-grafted hydrides [(≡SiO)₂Ta^(III)H], 1a, and [(≡SiO)₂Ta^(V)H₃], 1b, undergoes H/D exchange with D₂. In situ IR spectroscopy shows that the fully labelled compound [(≡SiO)₂Ta(ND)(ND₂)], 2-d, can be obtained by moderate heating (60 °C, 3 h) under D₂ atmosphere (550 torr, 300 eq. with respect to Ta), and that the exchange is reversible. The observed stretching and bending frequencies of 2-d are in agreement with the expected isotopic shift upon H/D replacement with respect to literature values reported for 2 and have been corroborated by the independent synthesis of 2-d by reaction of deuterated 1a and 1b with N₂ and D₂. Density functional theory (DFT) calculations, performed using a periodic or a cluster model, explored the structures and energetics of all minima involved in the reaction with H₂ and showed that among the explored pathways the energetically preferred mechanisms for H₂ reaction with [{(μ-O)[(HO)₂SiO]₂}Ta^(V)(NH)(NH₂)], 2q, is the heterolytic cleavage of either the imido Ta=N or the amido Ta-N bonds, to yield respectively [{(μ-O)[(HO)₂SiO]₂}TaH(NH₂)₂], 3q (ΔE = −9.5 kcal mol⁻¹ and ΔG_298K = +2.6 kcal mol⁻¹ with respect to 2q) and [{(μ-O)[(HO)₂SiO]₂}Ta(NH)(NH₃)], 4q (ΔE = −6.0 kcal mol⁻¹ and ΔG_298K = +7.9 kcal mol⁻¹ with respect to 2q). All activation barriers are moderate (between 17.7 and 30.2 kcal mol⁻¹) in agreement with the observed mild heating conditions necessary for the reaction to occur.     

Kinetic Studies on Oxirane Cleavage of Epoxidized Soybean Oil by Methanol and Characterization of Polyols

The kinetics of the oxirane cleavage of epoxidized soybean oil (ESO) by methanol (Me) without a catalyst was studied at 50, 60, 65, 70 °C. The rate of oxirane ring opening is given by k[Ep][Me]², where [Ep] and [Me] are the concentrations of oxiranes in ESO and methanol, respectively and k is a rate constant. From the temperature dependence of the kinetics thermodynamic parameters such as enthalpy (ΔH), entropy (ΔS), free energy of activation (ΔF) and activation energy (ΔE _a) were found to be 76.08 (±1.06) kJ mol⁻¹, −118.42 (±3.12) J mol⁻¹ k⁻¹, 111.39 (±2.86) kJ mol⁻¹, and 78.56 (±1.63) kJ mol⁻¹, respectively. The methoxylated polyols formed from the oxirane cleavage reaction , were liquid at room temperature and had three low temperature melting peaks. The results of chemical analysis via titration for residual oxiranes in the reaction system showed good agreement with IR spectroscopy especially the disappearance of epoxy groups at 825, 843 cm⁻¹ and the emergence of hydroxy groups at the OH characteristic absorption peak from 3,100 to 3,800 cm⁻¹.     

Fumigant and Contact Toxicities of Monoterpenes to <Emphasis Type="Italic">Sitophilus oryzae</Emphasis> (L.) and <Emphasis Type="Italic">Tribolium castaneum</Emphasis> (Herbst) and their Inhibitory Effects on Acetylcholinesterase Activity

A comparative study was conducted to assess the contact and fumigant toxicities of eleven monoterpenes on two important stored products insects—, Sitophilus oryzae, the rice weevil, and Tribolium castaneum, the rust red flour beetle. The monoterpenes included: camphene, (+)-camphor, (−)-carvone, 1-8-cineole, cuminaldehyde, (l)-fenchone, geraniol, (−)-limonene, (−)-linalool, (−)-menthol, and myrcene. The inhibitory effect of these compounds on acetylcholinesterase (AChE) activity also was examined to explore their possible mode(s) of toxic action. Although most of the compounds were toxic to S. oryzae and T. castaneum, their toxicity varied with insect species and with the bioassay test. In contact toxicity assays, (−)-carvone, geraniol, and cuminaldehyde showed the highest toxicity against S. oryzae with LC₅₀ values of 28.17, 28.76, and 42.08 μg/cm², respectively. (−)-Carvone (LC₅₀ = 19.80 μg/cm²) was the most effective compound against T. castaneum, followed by cuminaldehyde (LC₅₀ = 32.59 μg/cm²). In contrast, camphene, (+)-camphor, 1-8-cineole, and myrcene had weak activity against both insects (i.e., LC₅₀ values above 500 μg/cm²). In fumigant toxicity assays, 1-8-cineole was the most effective against S. oryzae and T. castaneum (LC₅₀ = 14.19 and 17.16 mg/l, respectively). Structure-toxicity investigations revealed that (−)-carvone—, a ketone—, had the highest contact toxicity against the both insects. 1-8-Cineole—, an ether—, was the most potent fumigant against both insects. In vitro inhibition studies of AChE from adults of S. oryzae showed that cuminaldehyde most effectively inhibited enzyme activity at the two tested concentrations (0.01 and 0.05 M) followed by 1-8-cineole, (−)-limonene, and (l)-fenchone. 1-8-Cineole was the most potent inhibitor of AChE activity from T. castaneum larvae followed by (−)-carvone and (−)-limonene. The results of the present study indicate that (−)-carvone, 1,8-cineole, cuminaldehyde, (l)-fenchone, and (−)-limonene could be effective biocontrol agents against S. oryzae and T. castaneum.     

Application of arrhenius kinetics to evaluate oxidative stability in vegetable oils by isothermal differential scanning calorimetry

In this study, 10 different vegetable oils were oxidized at four different isothermal temperatures (383, 393, 403, and 413 K) in a differential scanning calorimeter (DSC). The protocol involved oxidizing vegetable oils in a DSC cell with oxygen flow. A rapid increase in evolved heat was observed with an exothermic heat flow appearing during initiation of the oxidation reaction. From this resulting exotherm, the onset of oxidation time (T _o) was determined graphically by the DSC instrument. In our experimental data, linear relationships were determined by extrapolation of the log (T _o) against isothermal temperature. The rates of lipid oxidation were highly correlated with temperature. In addition, based on the Arrhenius equation and activated complex theory, reaction rate constants (k), activation energies (E _a), activation enthalpies (ΔH ^‡), and activation entropies (ΔS ^‡) for oxidative stability of vegetable oils were calculated. The E _a′, ΔH ^‡, and ΔS ^‡ for all vegetable oils ranged from 79 to −104 kJ mol⁻¹, from 76 to −101 kJ mol⁻¹, and from −99 to −20 J K⁻¹ mol⁻¹, respectively. Based on the results obtained, differential scanning calorimetry appears to be a useful new instrumental method for kinetic analysis of lipid oxidation in vegetable oil.     

Kinetic study of the polymerization of dimethyldiallylammonium chloride and acrylamide

The kinetics of the polymerization of dimethyldiallylammonium chloride (DMDAAC) and acrylamide (AM) with different monomer molar ratios initiated by an ammonium persulfate–sodium bisulfate redox complex in an aqueous solution were studied. The polymerization rate (R_p) equation, the activation energy (E_a), and the reactivity ratio were measured. The results show that when the n_DMDAAC:n_AM values were 1 : 9, 2 : 8, 3 : 7, 4 : 6, and 5 : 5, the copolymerization rate equation were R_p1 = k[M]^2.61[I_O]^0.51[I_R]^0.52, R_p2 = k[M]^2.70[I_O]^0.50[I_R]^0.53, R_p3 = k[M]^2.73[I_O]^0.50[I_R]^0.56, R_p4 = k[M]^2.77[I_O]^0.51[I_R]^0.59, and R_p5 = k[M]^2.84[I_O]^0.51[I_R]^0.61 (where [M] is the total monomer concentration, [I_O] is the oxidant concentration, and [I_R] is the reductant concentration), respectively when the temperature was 45°C. The E_a values were E_a1 = 79.10 kJ/mol, E_a2 = 81.39 kJ/mol, E_a3 = 85.15 kJ/mol, E_a4 = 88.88 kJ/mol, and E_a5 = 90.61 kJ/mol in the temperature range 35–55°C, respectively. The reactivity ratios of DMDAAC and AM were r_DMDAAC = 0.14 and r_AM = 6.11 when the temperature was 45°C. The structure of PDA was characterized by Fourier transform infrared spectroscopy and ¹H-NMR. The results of the kinetic parameters explained the differences in the copolymerization rate and intrinsic viscosity of PDA with different cationicities. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Kinetic study of the reaction between tocopheroxyl radical and unsaturated fatty acid esters in benzene

A kinetic study of the reaction between a tocopheroxyl radical and unsaturated fatty acid esters has been undertaken. The rates of allylic hydrogen abstraction from various unsaturated fatty acid esters (ethyl oleate2, ethyl linoleate3, ethyl linolenate4, and ethyl arachidonate5) by the tocopheroxyl radical (5,7-diisopropyltocopheroxyl6) in benzene have been determined spectrophotometrically. The second-order rate constants, k₃, obtained are 1.04×10⁻⁵ M⁻¹s⁻¹ for2, 1.82×10⁻² M⁻¹s⁻¹ for3, 3.84×10⁻² M⁻¹s⁻¹ for4, and 4.83×10⁻² M⁻¹s⁻¹ for5 at 25.0°C. Thus, the rate constants, k_abstr/H, given on an available hydrogen basis are k₃/4=2.60×10⁻⁶ M⁻¹s⁻¹ for2, k₃/2=9.10×10⁻³ M⁻¹s⁻¹ for3, k₃/4=9.60×10⁻³ M⁻¹s⁻¹ for4, and k₃/6=8.05×10⁻³ M⁻¹s⁻¹ for5. The k_abstr/H values obtained for the polyunsaturated fatty acid esters3,4, and5 containing H-atoms activated by two π-electron systems are similar to each other, and are about three orders of magnitude higher than that for the ethyl oleate2 containing H-atoms activated by a single π-system. From these results, it is suggested that the prooxidant effect of α-tocopherol in edible oils and fats may be induced by the above hydrogen abstraction reaction.     

Selective Reduction of NO with CO Over Titania Supported Transition Metal Oxide Catalysts

A series of transition metal oxides promoted titania catalysts (MO _x /TiO₂; M = Cr, Mn, Fe, Ni, Cu) were prepared by wet impregnation method using dilute solutions of metal nitrate precursors. The catalytic activity of these materials was evaluated for the selective catalytic reduction (SCR) of NO with CO as reductant in the presence of excess oxygen (2 vol.%). Among various promoted oxides, the MnO _x /TiO₂ system showed very promising catalytic activity for NO + CO reaction, giving higher than 90% NO conversion over a wide temperature window and at high space velocity (GHSV) of 50,000 h⁻¹. It is remarkable to note that the catalytic activity increased with oxygen, up to 4 vol.%, under these conditions leading primarily to nitrogen. Our TPR studies revealed the presence of mixed oxidation states of manganese on the catalyst surface. Characterization results indicated that the surface manganese oxide phase and the redox properties of the catalyst play an important role in final catalytic activity.     

Advances in electrochemical Fe(VI) synthesis and analysis

Hexavalent iron species (Fe(VI)) have been known for over a century, and have long-time been investigated as the oxidant for water purification, as the catalysts in organic synthesis and more recently as cathodic charge storage materials. Conventional Fe(VI) syntheses include solution phase oxidation (by hyphchlorite) of Fe(III), and the synthesis of less soluble super-irons by dissolution of FeO₄ ²⁻, and precipitation with alternate cations. This paper reviews a new electrochemical Fe(VI) synthesis route including both in situ and ex situ syntheses of Fe(VI) salts. The optimized electrolysis conditions for electrochemical Fe(VI) synthesis are summarized. Direct electrochemical synthesis of Fe(VI) compounds has several advantages of shorter synthesis time, simplicity, reduced costs (no chemical oxidant is required) and providing a possible pathway towards more electro-active and thermal stable Fe(VI) compounds. Fe(VI) analytical methodologies summarized in this paper are a range of electrochemical techniques. Fe(VI) compounds have been explored as energy storage cathode materials in both aqueous and non-aqueous phase in “super-iron” battery configurations. In this paper, electrochemical synthesis of reversible Fe(VI/III) thin film towards a rechargeable super-iron cathode is also summarized.     

The kinetics and mechanism of metal-catalyzed autoxidation

The autoxidation of organic compounds, RH, occurs by a radical-catalyzed chain reaction to give hydroperoxides, RO₂H, as primary products. The initial rate is -d[O₂]/dt = k_p[RH] {k_i[Cat]/k_t}^1/2, or in the presence of an inhibitor, (In), k_p[RH](k_i[Cat]/k_I[In]), where k_p is the chain propagation rate; k_i[Cat], the rate of radical catalysis; k_t chain termination rate; k_I[In] rate of inhibitor action. As oxidation proceeds the hydroperoxides break down to give further catalytically active radicals and eventually an autoxidation may reach a maximum rate of k _p ² [RH]²/fk_t, independent of the concentration or nature of the catalyst. Photosensitization, by forming singlet oxygen, can catalyze autoxidation by forming peroxides. Compounds of many transition metals, e.g., Co, Mn, Fe, act as secondary catalysts by promoting the rapid formation of radicals from RO₂H molecules by a one-electron transfer reaction RO-OH + M²⁺→RO· + M³⁺ + OH⁻ and the M³⁺ ions are then reconverted to M²⁺ ions giving further radicals. The overall catalytic activity of a metallic ion is controlled by the slower step of the M²⁺⇌M³⁺ + e redox cycle and depends on the electronic structures of the two ions concerned and on the ligand groups attached to them. These effects are discussed in detail since ligand molecules for transition metal ions can be selected so as either to promote or inhibit autoxidation. Special reference is made to biological catalysts, such as the porphyrins, found in food products. Direct activation of oxygen by metallic complexes rarely seems to occur, but direct oxidation of substrates by metallic compounds is possible. This leads to another redox cycle which is utilized in copper-containing enzymes. One of 28 papers presented at the Symposium, “Metal-Catalyzed Lipid Oxidation,” ISF-AOCS World Congress, Chicago, September 1970.     

An efficient method for a numerical description of virgin olive oil color with only two absorbance measurements

Four polynomial expressions are obtained that provide a good approximation and an easy, rapid calculation of the chromatic coordinates and the chroma—L ^*, a ^*, b ^*, and C—for the illuminant C and the standard observer, for a virgin or extra virgin olive oil; absorbance is measured at only 480 and 670 nm. These are as follows: L ^*=0.556458(A₄₈₀)²−2.51145A₄₈₀+0.55504(A₆₇₀)²−8.53016A₆₇₀+98.4089; a ^*=0.177372(A₄₈₀)²+2.1363A₄₈₀+1.43254(A₆₇₀)²−0.789231A₆₇₀−13.9246; b ^*=−16.0277(A₄₈₀)²+79.8932A₄₈₀−5.06558(A₆₇₀)²+3.36169A₆₇₀+31.9405; C=−15.8439(A₄₈₀)²+78.9312A₄₈₀−5.26784(A₆₇₀)²+3.56917A₆₇₀+33.3927. These give acceptable results, making the method a practical alternative to the extremely laborious Commission Internationale d’Eclairage (CIE) L ^* a ^* b ^* system, by which 391 absorbance values must be measured individually, nanometer by nanometer, before applying more complex equations. The validity of the proposed method has been confirmed by comparison, using a set of 20 sample oils different from the set of 25 oils used to generate the order of the equations. The variations between the values provided by the proposed and standard methods, respectively, had a mean of 0.00 for each of the chromatic variables—L ^* , a ^* , b ^* , and C; SD were moderate (0.71, 0.52, 1.22, and 1.22, respectively); the root mean square and the R ²-terms also confirmed the validity of the method.     

Autoxidation of methyl linoleate initiated by the ozonide of allylbenzene

Allylbenzene ozonide (ABO), a model for polyunsaturated fatty acid (PUFA) ozonides, initiates the autoxidation of methyl linoleate (18∶2 ME) at 37°C under 760 torr of oxygen. This process is inhibited by d-α-tocopherol (α-T) and 2,6-di-ert-butyl-4-methylphenol (BHT). The autoxidation was followed by the appearance of conjugated diene (CD), as well as by oxygen-uptake. The rates of autoxidation are proportional to the square root of ABO concentration, implying that the usual free radical autoxidation rate law is obeyed. Activation parameters for the thermal decomposition of ABO were determined under N₂ in the presence of radical scavengers and found to be E_a=28.2 ±0.3 kcal mol⁻¹ and log A=13.6±0.2; k_d (37°C) is calculated to be (5.1±0.3)×10⁻⁷ sec⁻¹. Autoxidation data are also reported for ozonides of 18∶2 ME and methyl oleate (18∶1 ME).     

Effect of growing area on pigment and phenolic fractions of virgin olive oils of the arbequina variety in Spain

The purpose of this investigation was to study differences in the chlorophyll, carotenoid, and phenolic fractions of virgin olive oils from the Arbequina variety cultivated in different olive growing areas of Spain. Virgin olive oil from Lleida was less heavily pigmented, and these oils showed more negative values for the ordinate a^* (of the CIELAB colorimetric system). Pheophytin a was the major chlorophyll pigment, and lutein was the major component of the carotenoid fraction in all oils analyzed. The chlorophyll a concentration in virgin olive oils from Lleida was 700 μg kg⁻¹, but was 175 μg kg⁻¹ in oils from Jaén, and 200 μg kg⁻¹ in oils from Tarragona. Finally, the chlorophyll a/chlorophyll b ratio was 9 in oils from Lleida and around 0.6 in the other two Arbequina olive oils. In relation to the phenolic fraction, the hydroxytyrosol and tyrosol contents were significantly higher in olive oils from Jaén (grown at higher altitude and precipitation rates). The secoiridoid derivatives showed a significantly higher concentration in olive oils from Tarragona, probably due to the low altitude where they grow, and finally the ratio of (dialdehydic form of elenolic acid linked to tyrosol)/lignans had a value of 1.4 in olive oils from Lleida, whereas this value was around 0.7 in the other Arbequina olive oils.     

Co-decorated carbon nanotube-supported Co–Mo–K sulfide catalyst for higher alcohol synthesis

Using chemical reduction-deposition method, a type of metallic cobalt-decorated multi-walled carbon nanotubes, noted as y%(mass percentage)Co/MWCNTs, was prepared. TEM, SEM and XRD measurements demonstrated that the metallic cobalt was evenly coated on the MWCNT substrate, with granule-diameter of the Co _x ⁰ -crystallites of 5–8 nm. Using the y%Co/MWCNTs as support, a type of supported Co–Mo–K sulfide catalysts, noted as x%(Co _i Mo _j K _k )/(y%Co/MWCNTs), for higher alcohol synthesis (HAS) was developed. It was experimentally shown that using the Co-modified MWCNTs in place of simple MWCNTs or activated carbon (AC) as the catalyst support led to a significant increase in activity of CO hydrogenation conversion and improvement in the selective formation of C₂₊-alcohols. Under the reaction condition of 5.0 MPa, 613 K, CO/H₂/N₂ = 45/45/10 (v/v) and GHSV = 3600 ml_STPh⁻¹ g _−cat. ⁻¹ , the observed STY of C_1–4-alcohols reached 154.1 mgh⁻¹g _−cat. ⁻¹ at 12.6% conversion of CO over the 11.6%(Co₁Mo₁K_0.6)/(6.4%Co/MWCNTs) catalyst, which was 1.76 and 2.33 times as high as that (87.7 and 66.1 mgh⁻¹g _−cat. ⁻¹ ) of the reference systems supported by simple MWCNTs and AC respectively. Ethanol became the predominant product of the CO hydrogenation, with carbon-based selectivity ratio of C_2–4-alcohols to CH₃OH reaching 3.6 in the products. It was experimentally found that using the Co-modified MWCNTs in place of simple MWCNTs or AC as the catalyst support caused little change in the apparent activation energy for the conversion of CO, but led to a slight increase in the molar percentage of catalytically active Mo-species (Mo⁴⁺) in the total Mo-amount at the surface of the functioning catalyst. Based upon the results of TPD investigation, it could be inferred that, under the reaction condition of HAS, there existed a considerably larger amount of adsorbed H-species and CO-species on the functioning catalyst, thus in favour of increasing the rate of a series of surface hydrogenation reactions in HAS.