CO在Ag掺杂的氧化锰八面体分子筛上吸附的TAP研究

利用产物瞬时分析反应器中进行的单脉冲实验, 考察了393～493 K温度范围内CO在Ag掺杂的氧化锰八面体分子筛上的吸附行为. 实验表明: CO在催化剂表面发生化学吸附, 并与晶格氧反应生成CO₂. 通过对该过程反应物及产物脉冲响应曲线的模拟, 得到了各基元反应的动力学参数. CO和CO₂在该催化剂表面的脱附活化能分别为83和31 kJ/mol, CO与晶格氧的反应活化能为116 kJ/mol.     

A theoretical study on the effect of intercalating sulfur atom and doping boron atom on the adsorption of hydrogen molecule on (10,0) single-walled carbon nanotubes

Adsorption of molecular hydrogen on single-walled carbon nanotube (SWCNT), sulfur-intercalated SWCNT (S-SWCNT), and boron-doped SWCNT (BSWCNT), have been studied by means of density functional theory (DFT). Two methods KMLYP and local density approximation (LDA) were used to calculate the binding energies. The most stable configuration of H₂ on the surface of pristine SWCNT was found to be on the top of a hexagonal at a distance of 3.54 Å in good agreement with the value of 3.44 Å reported by Han and Lee (Carbon, 2004, 42, 2169). KMLYP binding energies for the most stable configurations in cases of pristine SWCNT, S-SWCNT, and BSWCNT were found to be ?2.2 kJ mol^?1, ?3.5 kJ mol^?1, and ?3.5 kJ mol^?1, respectively, while LDA binding energies were found to be ?8.8 kJ mol^?1, ?9.7 kJ mol^?1, and ?4.1 kJ mol^?1, respectively. Increasing the polarizability of hydrogen molecule due to the presence of sulfur in sulfur intercalated SWCNT caused changes in the character of its bonding to sulfur atom and affected the binding energy. In H₂-BSWCNT system, stronger charge transfer caused stronger interaction between H₂ and BSWCNT to result a higher binding energy relative to the binding energy for H₂-SWCNT.     

Conductivity of crosslinked poly(N-vinylpyrrolidone) gel film containing surfactant as electrolyte salt

New polymeric solid electrolyte films, consisting of crosslinked poly(N-vinylpyrrolidone) (PVPD) as matrix, and surfactant, sodium deoxycholate (NaDC), lithium deoxycholate (LiDC), sodium laulylsulfate (R₁₂OSO₃Na), or sodium palmitate (R₁₅COONa) as electrolyte salt, are prepared; their basic structure and conductivity dependence on temperature are reported. The structure of the electrolytes is amorphous. Their conductivity is 3.1 × 10^?5 S cm^?1 (containing NaDC), 8.42 × 10^?6 S cm^?1 (LiDC), 2.18 × 10^?4 S cm^?1 (R₁₂OSO₃Na), and 7.27 × 10^?5 S cm^?1 (R₁₅COONa) at 20°C. Their temperature dependence of the conductivity is similar to that of liquid electrolyte rather than that of usual polymeric solid electrolyte, i.e., the WLF-type dependence. The values of activation energy of conductivity (E_a) were PVPD, 25.5 kJ mol^?1; PVPD/NaDC, 21.4 kJ mol^?1; PVPD/LiDC, 25.3 kJ mol^?1; PVPD/R₁₂OSO₃Na, 17.2 kJ mol^?1; PVPD/R₁₅COONa, 18.7 kJ mol^?1. © 1993 John Wiley & Sons, Inc.     

Adsorption of water on zeolites of different types

We have investigated the interaction of water with Na⁺-ion exchanged zeolites of different structures (LTA, FAU, ERI, MOR and MFI) by means of temperature-programmed desorption (TPD). The non-isothermal desorption of water shows, depending on the zeolite type, differently structured desorption profiles. In every case the profiles have, however, two main ranges. Using a regularization method, desorption energy distribution functions have been calculated. The desorption energy distributions between 42–60 kJ mol^?1, which can be attributed to a non-specific interaction of water, show two clearly distinguished energy ranges. The water desorption behaviour of this range correlates with the electronegativity of the zeolites and the average charge of the lattice oxygen atoms calculated by means of the electronegativity equalization method (EEM). The part of the desorption energy distributions in the range of 60–90 kJ mol^?1, reflecting interactions of water with Na⁺ cations, shows two more or less pronounced maxima. In agreement with vibrational spectroscopic studies in the far infrared region, it may be concluded that all samples under study possess at least two different cation sites.     

The structure and dissociation pathways of protonated methanol: An ab initio molecular orbital study

Ab initio molecular orbital calculations with moderately large polarization basis sets and including valence-electron correlation have been used to examine the structure and dissociation mechanisms of protonated methanol [CH₃OH₂]⁺. Stable isomers and transition structures have been characterized using gradient techniques. Protonated methanol is found to be the only stable isomer in the [CH₅O]⁺ potential surface. There is no evidence for a tightly-bound complex, [HOCH₂]⁺…?H₂, analogous to the preferred structure [CH₃]⁺…?H₂ of [CH₅]⁺. Protonated methanol is found to possess a pyramidal arrangement of bonds at the oxygen atom with a barrier to inversion of 8kJ mol^?1. The lowest energy fragmentation pathways are dissociation into methyl cation and water (predicted to require 284 kJ mol^?1 with zero reverse activation energy) and loss of molecular hydrogen (endothermic by 138 kJ mol^?1 but with a reverse activation barrier of 149 kJ mol^?1). The results offer a possible explanation as to why production of [CH₂OH]⁺ from the reaction of methyl cation with water is not observed. Other dissociation processes examined include loss of a hydrogen atom to yield the methylenoxonium radical cation or methanol radical cation (requiring 441 and 490 kJ mol^?1, respectively) and loss of a proton to yield neutral methanol (requiring 784 kJ mol^?1).     

Electroanalytical,kinetic, and mechanistic investigations of coordination-inspired electron transfer between Fe(II)/Cu(II)

Herein, we report that the thermodynamic barrier for solution-phase electron transfer (ET) between Cu(II) and Fe(II) in aqueous acidic media can be overcome through the addition of 2,9-dimethyl-1,10-phenanthroline (Neocuproine [NC]) to the reaction mixture. A detailed discussion of the kinetic and mechanistic aspects of this coordination-inspired ET is presented. We attribute the observed change in the thermodynamic feasibility to the change in the reduction potential of Cu(II)–Cu(I) couple on its ligation with NC. The reaction was found to be slow, following first-order kinetics with respect to each Cu(II) and Fe(II). In the presence of excess NC, the reaction was observed to proceed with a pseudo-second-order rate constant of 3.37?±?0.05?dm³?mol^?1?s^?1 at 298?K, with an activation barrier of ca. 26.22?kJ?mol^?1. The slow reaction is attributed to the significant reorganization energy associated with large-scale changes in the coordination sphere of the oxidant. A two-step mechanism that explains the experimental observations is proposed for the investigated reaction.     

Investigation of the Removal of Lead by Adsorption onto 1‐(2‐Thiazolylazo)‐2‐Naphthol (TAN) Imbedded Polyurethane Foam from Aqueous Solution

A new preconcentration method is presented for lead on TAN‐loaded polyurethane foam (PUF) and its measurement by differential pulse anodic stripping voltammetry (DPASV). The optimum sorption conditions of 1.29 × 10^?5 M solution of Pb(II) ions on TAN‐loaded PUF were investigated. The maximum sorption was observed at pH 7 with 20 minutes equilibrated time on 7.25 mg mL^?1 of TAN‐loaded foam. The kinetic study indicates that the overall sorption process was controlled by the intra‐particle diffusion process. The validity of Freundlich, Langmuir and Dubinin ‐ Radushkevich adsorption isotherms were tested. The Freundlich constants 1/n and K_F are evaluated to be 0.45 ±0.04 and (1.03 +0.61) × 10^?3 mol g^?1, respectively. The monolayer sorption capacity and adsorption constant related to the Langmuir isotherm are (1.38 ± 0.08) × 10^?5 mol g^?1 and (1.46 ± 0.27) × 10⁵ L mol^?1, respectively. The mean free energy of Pb(II) ions sorption on‐TAN loaded PUF is 11.04 ± 0.28 kJ mol^?1 indicating chemisorption phenomena. The effect of temperature on the sorption yields thermodynamics parameters of ΔH, ΔS and ΔG at 298 K that are 15.0 ± 1.4 kJ mol^?1, 74 ±5 J mol^?1 K^?1 and ‐7.37 ± 0.28 kJ mol^?1, respectively. The positive values of enthalpy (ΔH) and entropy (ΔS) indicate the endothermic sorption and stability of the sorbed complexes are entropy driven. However, the negative value of Gibb's free energy (ΔG) indicates the spontaneous nature of sorption. On the basis of these data, the sorption mechanism has been postulated. The effect of different foreign ions on the sorption and desorption studies were also carried out. The method was successfully applied for the determination of lead from different water samples at ng levels.     

Surface segregation measurements of In and S impurities from a dilute Cu(In,S) ternary alloy

The surface segregation of In and S from a dilute Cu(In,S) ternary alloy were measured using Auger electron spectroscopy coupled with a linear programmed heater. The alloy was linearly heated and cooled at constant rates. Segregation data of a linear heat run showed surface segregation of In that reached a maximum surface coverage of 25% followed by S, which reached a coverage of 30%. It was found that after In had reached a maximum surface coverage, it started to desegregate as soon as the S enriched the surface until In was completely replaced by S. The segregation parameters, namely, the pre‐exponential factor (D₀), activation energy (Q), segregation energy (ΔG?) and interaction energy (Ω) were extracted from the measured segregation data for both In and S segregation in Cu by simulating the measured segregation data with a theoretical segregation model (modified Darken model). The segregation parameters obtained for In segregation in Cu are D₀ = 1.8 ± 0.5 × 10^?5 m² s^?1, Q = 184.3 ± 1.0 kJ.mol^?1, ΔG? = ?61.4 ± 1.4 kJ.mol^‐1, Ω_Cu?In = 3.0 ± 0.4 kJ.mol^?1; for S segregation in Cu the parameters are D₀ = 8.9 ± 0.5 × 10^?3 m² s^?1, Q = 212.8 ± 3.0 kJ.mol^?1, ΔG? = ?120.0 ± 3.5 kJ.mol^?1, Ω_Cu?S = 23.0 ± 2.0 kJ mol^?1 and the In and S interaction parameter is Ω_In?S = ?4.0 ± 0.5 kJ.mol^?1. The initial parameters used for the Darken calculations were extracted from fits performed with the Fick's and Guttmann model. Copyright © 2013 John Wiley & Sons, Ltd.     

Modeling the hydration and proton transport in solid electrolytes based on phenolsulfonic acids

Geometrical and energetic characteristics of crystal hydrates of individual aromatic sulfonic acids and their complexes with poly(vinyl alcohol) as well as the paths for the proton transport in them are calculated in the framework of the density functional theory (version B3LYP) employing the 6-31G^** basis set. The energy of attachment of water to ortho-substituted aromatic sulfonic acids is demonstrated to diminish from 74.4 to 54.8 kJ mol^?1 in the following series of substituents: -OH,-F,-CH₃,-H,-Cl, and -COOH. For the dimers that comprise individual phenolsulfonic acids, the energy of attachment of one water molecule to the SO₃H group is estimated to be equal to 92–105 kJ mol^?1. In the dimers comprising individual phenolsulfonic acids, the specific energy of intermolecular bonds (bond energy per monomer molecule) is found to be equal to 49.3 and 58.5 kJ mol^?1 for, respectively, phenol-2,4-disulfo and phenol-2-sulfo acids. During the formation of polymer membranes based on poly(vinyl alcohol) and phenolsulfonic acids, it is energetically favorable that at least one water molecule should remain in the vicinity of the SO₃H fragment. According to the calculations, the proton migration along the SO₃H group in anhydrous environment is hampered by a barrier of 125–132 kJ mol^?1. In the presence of water, the proton conductivity is of a relay character, with an activation barrier equal to 21–33 kJ mol^?1. The latter value is close to experimental data (17–25 kJ mol^?1).     

Mass spectrometric evolved gas analysis (MSEGA) study of the thermal decomposition of poly(1,2-acenaphthenediylidene) and poly(1,2-acenaphthylenylene) in vacuo

A mass spectrometric study of the thermal decompositions in vacuo of two polyene polymers, poly(1,2-acenaphthenediylidene)-I and poly(1,2-acenaphthylenylene)-II, was performed in order to establish the differences between their structures. Evolution of repeating units from a chain depropagation process of both polymers was observed. Annealing of the polymers prior to decomposition changed the temperature at which maxima were observed on the MSEGA ion current temperature profiles. These profiles of both polymers after annealing became more similar in shape and temperature location. These changes in MSEGA behaviour as a result of annealing can be attributed to an equalisation of the single and double bonds in the structure of the polymers. The kinetic study of the thermal decomposition of non-annealed polymers showed that the decomposition reaction for polymer I is isokinetic, i.e. of the same kinetic mechanism, when the fraction of sample decomposed “α” is in the range 0.4–0.7 with values of 127.8 ± 3.6 kJ mol^?1 for the activation energy and 2.6 ± 2.2 × l0⁷ s^?1 for the A factor. Polymer II did not show clearcut isokinetic behaviour, the activation energy increasing from 99.4 kJ mol^?1 at α = 0.4–113.5 kJ mol^?1 at α = 0.7. This change is attributed to the structure of the polymer altering during the course of the decomposition. The differences in the thermal properties lead to the conclusion that there is a bond alternation in the polyene chains of both polymers.     

The chromatographic retention of H and D atoms on quartz

The chromatographic retention of H and D atoms has been observed in a quartz tube using argon as a carrier gas for D and six different gases for H. The results give equilibrium constants for the reversible adsorption of H and D on quartz as well as the rates of desorption. Self-consistent conclusions can be drawn from the data. The adsorption energy appears to be ca. 50 kJ mol^?1 indicating weak chemisorption. The observations are consistent with vibration frequencies on the surface of around 700–900 cm^?1 for D. and around 1000–1300 cm^?1 for H. It appears that only a fraction of the surface atoms (ca. 10^?2) act as adsorption sites.     

Measurements of electrical conductivity in solid bromine and iodine

Measurements of the electrical conductivity were performed with bromine and iodine in the liquid and the solid states, both containing low concentrations of the corresponding halide ions. In bromine the specific conductivity increases dramatically upon solidification and in iodine it changes only slightly. In both systems the conductivity in the solid is rather high, with remarkably low temperature coefficients, pointing to an unusual mechanism of conduction (of the Grotthuss type) requiring very little movement of the heavy nuclei while the charge is transferred. In mixtures of bromine with a small amount of nitrobenzene (NB) an equivalent conductivity as high as 12 cm² mol^?1 Ω^?1 was observed at ?25°C. In iodine the specific conductivity reached a value of about 0.01 Ω^?1 cm^?1 at 100°C. The energy of activation for conduction in bromine down to ?40°C was found to be about 23 kJ mol^?1, increasing sharply below this temperature. In iodine, values of about 21–27 kJ mol^?1 were observed over the whole temperature range measured.     

Kinetische untersuchung der reversiblen dimerisierung von o-phenylendioxidimethylsilan

The reversible dimerisation of o-phenylenedioxydimethylsilane (2,2-dimethyl-1,3,2-benzodioxasilole) has been studied by ¹H NMR spectroscopy. The kinetics of this reaction can be described quantitatively by a bimolecular 10-ring formulation reaction and a monomolecular backreaction. The thermodynamic and kinetic parameters are: ΔH⁰ = ?43 kJ mol^?1; ΔS⁰ = ?112 J mol^?1 K^?1; ΔG⁰₂₉₈ = ?9.6 kJ mol^?1; ΔH³₂₉₈ = 57 kJ mol^?1; ΔS³₂₉₈ = ?129 J mol^?1 K^?1; ΔG³₂₉₈ = 96 kJ mol^?1; E_a = 60 kJ mol^?1; A = 3.17 × 10⁶ l mol^?1 s^?1. Remarkable is the low activation energy of formation of the ten-membered ring, considering that two SiO bonds have to be cleaved during the reaction. Transition states and possible structures of the ten-membered heterocycle are discussed.     

Kinetics and mechanism of the oxidation of iron(II) ion by chlorine dioxide in aqueous solution

The mechanism by which an excess of iron(II) ion reacts with aqueous chlorine dioxide to produce iron(III) ion and chloride ion has been determined. The reaction proceeds via the formation of chlorite ion, which in turn reacts with additional iron(II) to produce the observed products. The first step of the process, the reduction of chlorine dioxide to chlorite ion, is fast compared to the subsequent reduction of chlorite by iron(II). The overall stoichiometry is The rate is independent of pH over the range from 3.5 to 7.5, but the reaction is assisted by the presence of acetate ion. Thus the rate law is given by At an ionic strength of 2.0 M and at 25°C, k_u = (3.9 ± 0.1) × 10³ L mol^?1 s^?1 and k_c = (6 ± 1) × 10⁴ L mol^?1 s^?1. The formation constant for the acetatoiron(II) complex, K_f, at an ionic strength of 2.0 M and 25°C was found to be (4.8 ± 0.8) × 10^?2 L mol^?1. The activation parameters for the reaction were determined and compared to those for iron(II) ion reacting directly with chlorite ion. At 0.1 M ionic strength, the activation parameters for the two reactions were found to be identical within experimental error. The values of ΔH? and ΔS? are 64 ± 3 kJ mol^?1 and + 40 ± 10 J K^?1 mol^?1 respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 554–565, 2004     

Sequential segregation of Sn and Sb in a Cu(111) single crystal

The sequential segregation of Sn and Sb to the surface of a Cu(111) single crystal was measured in the temperature range 400–1100 K by Auger electron spectroscopy. It was found that Sn with the higher diffusion coefficient first segregates to the surface and then is replaced by the slower‐segregating Sb. The results were fitted by a ternary segregation model yielding segregation energies (ΔG_Sn = 76.3 kJ mol^?1, ΔG_Sb = 95.9 kJ mol^?1), interaction parameters (Ω_SnCu = 3.8 kJ mol^?1, Ω_SbCu = 16.2 kJ mol^?1, Ω_SnSb = ?5.3 kJ mol^?1) and diffusion coefficients (D_0(Sn) = 1.8 × 10^?5 m² s^?1, E_Sn = 173 kJ mol^?1, D_0(Sb) = 6.0 × 10^?5 m² s^?1, E_Sb = 205 kJ mol^?1) for both species. The validity of the interaction coefficients and segregation energies was verified using the Guttman equations for equilibrium segregation in ternary systems. Copyright © 2003 John Wiley & Sons, Ltd.     

Reduction from copper(II) to copper(I) upon collisional activation of (pyridine)2CuCl+

Electrospray ionization of dilute aqueous solutions of copper(II) chloride‐containing traces of pyridine (py) as well as ammonia permits the generation of the gaseous ions (py)₂Cu⁺ and (py)₂CuCl⁺, of which the latter is a formal copper(II) compound, whereas the former contains copper(I). Collision‐induced dissociation of the mass‐selected ions in an ion‐trap mass spectrometer (IT‐MS) leads to a loss of pyridine from (py)₂Cu⁺, whereas an expulsion of atomic chlorine largely prevails for (py)₂CuCl⁺. Theoretical studies using density functional theory predict a bond dissociation energy (BDE) of BDE[(py)₂Cu⁺ ‐Cl] = 125 kJ mol^?1, whereas the pyridine ligand is bound significantly stronger, i.e. BDE[(py)CuCl⁺ ‐py] = 194 kJ mol^?1 and BDE[(py)Cu⁺ ‐py] = 242 kJ mol^?1. The results are discussed with regard to the influence of the solvation on the stability of the Cu^I/Cu^II redox couple. Copyright © 2010 John Wiley & Sons, Ltd.     

Kinetics of Lab Prepared Manganese Oxide Catalyzed Oxidation of Benzyl Alcohol in the Liquid Phase

The oxidation of benzyl alcohol in the liquid phase was studied over manganese oxide catalyst using molecular oxygen as an oxidant. Manganese oxide was prepared by a mechanochemical process in solid state and was characterized by chemical and physical techniques. The catalytic performance of manganese oxide was explored by carrying out the oxidation of benzyl alcohol at 323–373 K temperature and 34–101 kPa partial pressure of oxygen. Benzaldehyde and benzoic acid were identified as the reaction products. Typical batch reactor kinetic data were obtained and fitted to the Langmuir–Hinshelwood, Eley–Rideal, and Mars–van Krevelene models of heterogeneously catalyzed reactions. The Langmuir–Hinshelwood model was found to give a better fit. Adsorption of benzyl alcohol at the surface of the catalyst followed the Langmuir adsorption isotherm. The heat of adsorption for benzyl alcohol was determined as –18.14 kJ mol^?1. The adsorption of oxygen followed the Temkin adsorption isotherm. The maximum heat of adsorption for oxygen was –31.12 kJ mol^?1. The value of activation energy was 71.18 kJ mol^?1, which was apparently free from the influence of the heat of adsorption of both benzyl alcohol and oxygen.     

Conformational polymorphs of 22‐cyano‐N‐methyl‐5‐phenylpent‐2‐en‐4‐ynamide

Although the two polymorphic modifications, (I) and (II), of the title compound, C₁₃H₁₀N₂O, crystallize in the same space group (P2₁/c), their asymmetric units have Z′ values of 1 and 2, respectively. These are conformational polymorphs, since the mol­ecules in phases (I) and (II) adopt different rotations of the phenyl ring with respect the central 2‐cyano­carboxy­amino­prop‐2‐enyl fragment. Calculations of crystal packing using Cerius² [Molecular Simulations (1999). 9685 Scranton Road, San Diego, CA 92121, USA] have shown that (I) is more stable than (II), by 1.3 kcal mol^?1 for the crystallographically determined structures and by 1.56 kcal mol^?1 for the optimized structures (1 kcal mol^?1 = 4.184 kJ mol^?1). This difference is mainly attributed to the different strengths of the hydrogen bonding in the two forms.     

O2 Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

This paper reports the computed O₂ binding to heme, which for the first time explains experimental enthalpies for this process of central importance to bioinorganic chemistry. All four spin states along the relaxed Fe? O₂‐binding curves were optimized using the full heme system with dispersion, thermodynamic, and scalar‐relativistic corrections, applying several density functionals. When including all these physical terms, the experimental enthalpy of O₂ binding (?59 kJ mol^?1) is closely reproduced by TPSSh‐D3 (?66 kJ mol^?1). Dispersion changes the potential energy surfaces and leads to the correct electronic singlet and heptet states for bound and dissociated O₂. The experimental activation enthalpy of dissociation (～82 kJ mol^?1) was also accurately computed (～75 kJ mol^?1) with an actual barrier height of ～60 kJ mol^?1 plus a vibrational component of ～10 and ～5 kJ mol^?1 due to the spin‐forbidden nature of the process, explaining the experimentally observed difference of ～20 kJ mol^?1 in enthalpies of binding and activation. Most importantly, the work shows how the nearly degenerate singlet and triplet states increase crossover probability up to ～0.5 and accelerate binding by ～100 times, explaining why the spin‐forbidden binding of O₂ to heme, so fundamental to higher life forms, is fast and reversible.     

Enthalpy Change of Allosteric Transition in Human Haemoglobin A

Oxygen equilibria of haemoglobin were analysed according to a binding isotherm proposed by Amire ( Bull. Chem. Soc. Jpn. 1994, 67, 7 )¹ to obtain the intrinsic oxygen association constants to the molecule. Two sets of binding sites in haemoglobin were identified, which were ascribed to R₂ and T forms of the molecule. The average intrinsic association constants determined as a function of temperature gave a heat of oxygenation of‐76 ± 4 kJ mol^?;1 (tetramer). A microcalorimetrically determined heat of deoxygenation of oxyhaemoglobin by dithionite gave ?267 ± 10 kJ mol^?1 (tetramer). From these results, the heat of allostery of ?234 ± 24 kJ mol^?1 for haemoglobin tetramer was obtained, yielding allosteric energy per salt bridge of‐29 ± 3 kJ. This result suggests that salt‐bridge may, in fact, be thermochemically equivalent to hydrogen bonds.