Catalysis of Carbon–Gas Reactions

The characteristic features on the catalysis of carbon–gas reactions has been studied by combining various techniques such as transient kinetics, temperature-programmed desorption and others. Some of recent achievements are presented to comprehend the state of the art. Many industrial processes associated with catalytic carbon–gas reactions are then discussed in relation to the fundamental chemistry of catalysis.     

DFT Calculations of Vibrational Frequencies of Carbon–Nitrogen Clusters: Raman Spectra of Carbon Nitrides

We have performed the calculation of structures of clusters containing carbon and nitrogen atoms. We determine the bond lengths in each case. We also calculate the vibrational frequencies of all of the clusters. We compare the calculated values of the vibrational frequencies with those measured by the Raman spectra of amorphous carbon nitrides. Some of the calculated frequencies are in agreement with those measured. We identity that linear structures and hence “back bones” are present in the glassy state.     

Hypervalent-Iodine-Mediated Carbon–Carbon Bond Cleavage and Dearomatization of 9H-Fluoren-9-ols

A transition-metal-free synthesis of spiro compounds from 9H-fluoren-9-ols mediated by hypervalent iodine is reported. In this reaction, an unprecedented β-carbon elimination of tertiary alkoxyliodine(III) to form new diaryliodonium salts is proposed. The obtained phenol intermediates undergo oxidative dearomatization to furnish a class of oxo-spiro compounds. This domino reaction significantly increases the complexity of these molecules and shows excellent regio- and stereoselectivity.     

Microwave-Enhanced Hydrogenation of Carbon–Carbon Double Bonds in Single-Stranded Polymers by p-Tosylhydrazide

A rapid and efficient method for the hydrogenation of the backbones of various single-stranded polymers with p-tosylhydrazide is developed using microwave irradiation, through which the corresponding saturated and more flexible polymers are obtained in good to excellent yields.     

Adsorption and Structural Properties of Mineral–Carbon Sorbents

In the present work an attempt was made to obtain mineral–carbon sorbents by thermal decompositon. The mineral matrix for the sorbents (aluminium hydroxide) was based on petrochemical waste stream containing considerable amounts of aluminium chloride. Reference tests were carried out with a model solution prepared with the use of analytical grade AlCl₃. Atactic polypropylene and hydrocarbon mixtures obtained in the flotation of petrochemical waste waters were used as carbon-containing raw materials. The aim of this work was to determine the adsorption and structural characteristics of the complex sorbents and to check the possibility of evaluation of their hydrophobic-hydrophilic properties. This revised version was published online in August 2006 with corrections to the Cover Date.     

Direct Mechanism of the First Carbon–Carbon Bond Formation in the Methanol-to-Hydrocarbons Process

In the past two decades, the reaction mechanism of C−C bond formation from either methanol or dimethyl ether (DME) in the methanol-to-hydrocarbons (MTH) process has been a highly controversial issue. Described here is the first observation of a surface methyleneoxy analogue, originating from the surface-activated DME, by in situ solid-state NMR spectroscopy, a species crucial to the first C−C bond formation in the MTH process. New insights into the first C−C bond formation were provided, thus suggesting DME/methanol activation and direct C−C bond formation by an interesting synergetic mechanism, involving C−H bond breakage and C−C bond coupling during the initial methanol reaction within the chemical environment of the zeolite catalyst.     

Use of Iodosobenzene in Combination with Vilsmeier–Haack Reagent in Carbon–Carbon Bond Cleavage of Dehydroacetic Acid and Its Analogue

The reaction of dehydroacetic acid with iodosobenzene in combination with Vilsmeier–Haack reagent offers a new and convenient method for C‐C bond cleavage with the formation of 3‐chloro‐4‐hydroxy‐6‐methyl‐2H‐pyran‐2‐one.     

Adsorption of Carbon Dioxide on Activated Carbon

The adsorption of CO2 on a raw activated carbon A and three modified activated carbon samples B, C, and D at temperatures ranging from 303 to 333 K and the thermodynamics of adsorption have been investigated using a vacuum adsorption apparatus in order to obtain more information about the effect of CO2 on removal of organic sulfur-containing compounds in industrial gases. The active ingredients impregnated in the carbon samples show significant influence on the adsorption for CO2 and its volumes adsorbed on modified carbon samples B, C, and D are all larger than that on the raw carbon sample A. On the other hand, the physical parameters such as surface area, pore volume, and micropore volume of carbon samples show no influence on the adsorbed amount of CO2. The Dubinin-Radushkevich (D-R) equation was the best model for fitting the adsorption data on carbon samples A and B, while the Preundlich equation was the best fit for the adsorption on carbon samples C and D. The isosteric heats of adsorption on carbon samples A, B, C, and D derived from the adsorption isotherms using the Clapeyron equation decreased slightly increasing surface loading. The heat of adsorption lay between 10.5 and 28.4 kJ/mol, with the carbon sample D having the highest value at all surface coverages that were studied. The observed entropy change associated with the adsorption for the carbon samples A, B, and C (above the surface coverage of 7 ml/g) was lower than the theoretical value for mobile adsorption. However, it was higher than the theoretical value for mobile adsorption but lower than the theoretical value for localized adsorption for carbon sample D.     

Dynamic Mechanical Properties of Activated Carbon–Filled Epoxy Nanocomposites

Nano-activated carbons obtained from oil palm empty fiber bunch (AC-EFB), bamboo stem (AC-BS), and coconut shells (AC-CNS) were reinforced in epoxy matrix to fabricate epoxy nanocomposites. The dynamic mechanical analysis of epoxy nanocomposites was carried out, and 5% AC-CNS treated with KOH-filled epoxy composites displayed the highest storage modulus of all the activated carbon–filled epoxy composites. The incorporation of a small amount of AC-BS, AC-EFB, and AC-CNS to the epoxy matrix enhanced the damping characteristics of the epoxy nanocomposites. The 5% AC-EFB treated with H₃PO₄ filled epoxy composites showed the highest glass transition temperature (T_g) in all temperature ranges.     

Determination of Formaldehyde with a Platinum–Palladium–Graphene Nanocomposite Glassy Carbon Electrode

The oxidation of formaldehyde on a platinum (Pt)–palladium (Pd)–graphene nanocomposite glassy carbon electrode prepared by chemical reduction was characterized in 0.5?M sulfuric acid. The surface and morphology of the catalyst were characterized by transmission electron microscopy, Raman spectroscopy, and X-ray diffraction. Bimetallic Pt–Pd nanoparticles were uniformly dispersed on the graphene sheets. Energy-dispersed X-ray spectroscopy was used to characterize the metal composition of the nanocomposite. The electrocatalytical characteristics of the modified electrode were investigated by cyclic voltammetry. The results show that the electrode displayed high activity for the oxidation of formaldehyde in sulfuric acid with a linear relationship from 4.50?µM to 0.180?mM and a detection limit of 2.85?µM. The low detection limit, wide linear dynamic range, and high sensitivity of the modified electrode suggests further applications.     

Spectroscopic Investigation of Chalcogen Bonding: Halide–Carbon Disulfide Complexes

A combined experimental and theoretical approach has been used to study intermolecular chalcogen bonding. Specifically, the chalcogen bonding occurring between halide anions and CS₂ molecules has been investigated using both anion photoelectron spectroscopy and high-level CCSD(T) calculations. The relative strength of the chalcogen bond has been determined computationally using the complex dissociation energies as well as experimentally using the electron stabilisation energies. The anion complexes featured dissociation energies on the order of 47 kJ/mol to 37 kJ/mol, decreasing with increasing halide size. Additionally, the corresponding neutral complexes have been examined computationally, and show three loosely-bound structural motifs and a molecular radical.     

Thermodynamic Investigation of Phase Equilibria in Metal Carbonate–Water–Carbon Dioxide Systems

Summary.  Solubility measurements as a function of temperature have been shown to be a powerful tool for the determination of thermodynamic properties of sparingly-soluble transition metal carbonates. In contrast to calorimetric methods, such as solution calorimetry or drop calorimetry, the evaluation of solubility data avoids many systematic errors, yielding the enthalpy of solution at 298.15 K with an estimated uncertainty of ±3 kJ · mol⁻¹. A comprehensive set of thermodynamic data for otavite (CdCO₃), smithsonite (ZnCO₃), hydrozincite (Zn₅(OH)₆(CO₃)₂), malachite (Cu₂(OH)₂CO₃), azurite (Cu₃(OH)₂(CO₃)₂), and siderite (FeCO₃) was derived. Literature values for the standard enthalpy of formation of malachite and azurite were disproved by these solubility experiments, and revised values are recommended. In the case of siderite, data for the standard enthalpy of formation given by various data bases deviate from each other by more than 10 kJ · mol⁻¹ which can be attributed to a discrepancy in the auxiliary data for the Fe²⁺ ion. A critical evaluation of solubility data from various literature sources results in an optimized value for the standard enthalpy of formation for siderite. The Davies approximation, the specific ion-interaction theory, and the Pitzer concept are used for the extrapolation of the solubility constants to zero ionic strength in order to obtain standard thermodynamic properties valid at infinite dilution, T = 298.15 K, and p = 10⁵ Pa. The application of these electrolyte models to both homogeneous and heterogeneous (solid-solute) equilibria in aqueous solution is reviewed. Received June 26, 2001. Accepted July 2, 2001     

Thermodynamic Investigation of Phase Equilibria in Metal Carbonate–Water–Carbon Dioxide Systems

 Solubility measurements as a function of temperature have been shown to be a powerful tool for the determination of thermodynamic properties of sparingly-soluble transition metal carbonates. In contrast to calorimetric methods, such as solution calorimetry or drop calorimetry, the evaluation of solubility data avoids many systematic errors, yielding the enthalpy of solution at 298.15 K with an estimated uncertainty of ±3 kJ · mol⁻¹. A comprehensive set of thermodynamic data for otavite (CdCO₃), smithsonite (ZnCO₃), hydrozincite (Zn₅(OH)₆(CO₃)₂), malachite (Cu₂(OH)₂CO₃), azurite (Cu₃(OH)₂(CO₃)₂), and siderite (FeCO₃) was derived. Literature values for the standard enthalpy of formation of malachite and azurite were disproved by these solubility experiments, and revised values are recommended. In the case of siderite, data for the standard enthalpy of formation given by various data bases deviate from each other by more than 10 kJ · mol⁻¹ which can be attributed to a discrepancy in the auxiliary data for the Fe²⁺ ion. A critical evaluation of solubility data from various literature sources results in an optimized value for the standard enthalpy of formation for siderite. The Davies approximation, the specific ion-interaction theory, and the Pitzer concept are used for the extrapolation of the solubility constants to zero ionic strength in order to obtain standard thermodynamic properties valid at infinite dilution, T = 298.15 K, and p = 10⁵ Pa. The application of these electrolyte models to both homogeneous and heterogeneous (solid-solute) equilibria in aqueous solution is reviewed.     

Chemical and Transport Properties of Carbon–Oxygen–Hydrogen Plasmas in Isochoric Conditions

The composition and transport properties of CO₂, CO, CH₄, CO + Ar (50 vol%), CO + Fe (50 vol%) have been calculated at constant volume assuming local thermodynamic equilibrium (LTE). Except at low temperature (T < 3000 K), when the formation of condensed species or more complex molecules can occur, pressure increases with temperature at constant volume. For example, for 1 mol of CH₄ starting at 0.1 MPa and 298 K the pressure can reach 40 MPa at 20,000 K. The consequence is a shift to higher temperatures of dissociation and ionization. The electrical conductivity σ_e at constant volume increases drastically relative to that obtained at 0.1 MPa over 15,000 K, in spite of the decrease of the electron density n_e This is due to the increase in the neutral species density. n_i, with a much lower electron-neutral species collision cross section σ_ei (σ_e is inversely proportional to n_i,σ_ei). The viscosity always exhibits a maximum when the ionization degree increases over 1–30%, but this maximum is shifted to higher temperatures and its peak value is higher. The thermal conductivity peaks due to dissociation and ionization are shifted to higher temperatures and their values are reduced compared to those obtained at constant pressure.     

Electrochemical Determination of Uric Acid Using a Multiwalled Carbon Nanotube Platinum–Nickel Alloy Glassy Carbon Electrode

Platinum–nickel nanoparticles were synthesized by a reduction procedure. The Pt–Ni/C composite was characterized by X-ray diffraction, infrared spectroscopy, transmission electron microscopy, and electrochemical analysis. The measurements show that the Pt–Ni/multiwalled carbon nanotubes provided higher electrocatalytic activity for the oxidation of uric acid than Pt–Ni/carbon black. The sensor prepared from the characterized material provided a long linear dynamic range from 0.1 to 240.4?µM with a detection limit of 0.03?µM and a sensitivity of 41.21?µA?mM^?1?cm^?2. The reported modified electrode also provided excellent selectivity, good stability, and satisfactory reproducibility for the determination of uric acid.     

Electrocatalytic Response of Dopamine at an Iron Nanoparticles–Nafion–Modified Carbon Paste Electrode

Abstract

Iron nanoparticles (INPs) were dispersed in Nafion solution to obtain a homogeneous INP-Nafion dispersion, and then a drop of this dispersion was cast on the surface of a carbon paste electrode (CPE) to fabricate an INP-Nafion-modified electrode. The electrochemical behavior of dopamine (DA) at this modified electrode was studied by cyclic voltammetry in a pH 7.0 Britton-Robinson (B-R) buffer solution. The result showed that the modified CPE exhibited an obvious electrocatalytical response toward DA, with the anodic and cathodic peak potentials shifted negatively and positively respectively, and great enhance of the peak currents at the scan rate of 100 mV s^?1. The effects of carbon paste constitution, amount of the dispersion, pH, and scan rate were investigated. Under the optimum experimental conditions, the peak currents determined by differential pulse voltammetry showed an excellent linear relationship with DA concentration in the range from 10 to 110 µM with the detection limit of 3.3 µM. In addition, ascorbic acid and some other possible interferents did not interfere with the voltammetric sensing of DA, and this method also had good stability and reproducibility.     

Electrochemical Characterization of CoHP–Si Incorporated into a Carbon Paste Electrode

Reduction of dioxygen at a carbon paste electrode (CPE) modified with cobalt hematoporphyrin complex immobilized on silica gel (CoHP–Si) was studied by cyclic voltammetry and rotating disk electrode. In 0.5molL^–1 KCl solution, the supported complex showed significant catalytic activity towards four-electron reduction of O₂ to H₂O at a relatively high pH (5.4). The reduction of dioxygen proceeds at a more negative potential (–0.375V) than the redox reaction Co^III/Co^II (0.464V), indicating that the mechanism does not involve the complex as an electron transfer mediator. Catalytic activity of CoHP–Si towards reduction of H₂O₂ was tested, but no activity was observed.Received October 26, 2002; accepted March 10, 2003 Published online July 16, 2003     

Synthesis and Properties of Composite Polyaniline–Nafion Films on Glassy Carbon

Information on the synthesis of a polyaniline film on glassy carbon covered with a Nafion film is obtained. The effect of electrochemical synthesis conditions on the process is studied. The relationship between these conditions and properties of obtained composite polyaniline–Nafion films is revealed.     

Nitrogen–Carbon Bond Formation by Reactions of a Titanium–Potassium Dinitrogen Complex with Carbon Dioxide,tert-Butyl Isocyanate,and Phenylallene

Nitrogen–carbon bond-forming reactions at coordinated dinitrogen in a bifunctional titanium–potassium system are reported. A titanium atrane complex with a tris(aryloxide)methyl ligand ( 1 ) was treated with two equivalents of potassium naphthalenide under N₂ atmosphere to generate a bifunctional complex ( 2 ) in which N₂ binds end-on to two titanium centers and side-on to three potassium cations. Dinitrogen complex 2 reacted with carbon dioxide, tert-butyl isocyanate, and phenylallene, forming nitrogen–carbon bonds and affording diverse N-functionalized products. The reaction of 2 with CO₂ followed by addition of Me₃SiCl resulted in the formation of the starting complex 1 with concomitant release of silylated carboxyl hydrazines while the reaction with two equivalents of tert-butyl isocyanate proceeded by insertion into the Ti−N bonds. Treatment of 2 with phenylallene afforded vinyl-substituted hydrazido complexes.     

Carbon–Carbon Bond Formation via Catalytically Generated Aminocarbene Complexes: Rhodium-Catalyzed Hydroaminative Cyclization of Enynes with Secondary Amines

We report a hydroaminative cyclization of enynes using phosphine-quinolinolato rhodium catalysts. The hydroaminative cyclization of 2-vinylphenylacetylene derivatives with secondary amines gives 2-aminoindenes in good yields. The reaction is considered to proceed through carbon–carbon bond formation on a catalytically generated aminocarbene ligand.