Gas diffusion hindrances on Ni cermet anode in contact with Zr<Subscript>0.84</Subscript>Y<Subscript>0.16</Subscript>O<Subscript>1.92</Subscript> solid electrolyte

The electrochemical behavior of Ni cermet electrode with CeO_{2 ? x} additive in contact with YSZ electrode was studied by means of impedance spectroscopy in H₂, H₂O, CO₂, CO, He, and Ar gas media of various composition within the temperature range of 700 to 950°C. Near the equilibrium potential, the electrochemical impedance spectra of the studied electrodes indicate to three stages of electrode reaction. The polarization conductivity of the low-frequency stage of electrode reaction (σ_lf) is characterized with the following regularities: (a) temperature dependence of σ_lf has a positive slope in Arrhenius coordinates; (b) σ_lf increases upon replacement of gas mixture with lower mutual diffusion coefficient by mixture with higher mutual diffusion coefficient, while polarization conductivity values of other stages remain practically invariable; (c) concentration relationships of 1/σ_lfrecorded for constant activity of oxygen in the gas phase are linear in the 1/σ_lf vs. 1/P _{CO 2} (P _CO) coordinates; (d) no low-frequency stage of the electrode reaction is observed upon electrochemical inflow (outflow) of the gas reagents (reaction products) to (from) the test electrodes (current passing through closely pressed specimens and central specimen impedance measurement); and (e) no change in the gas flow rate affects σ_lf value. The observed regularities were explained by assuming the gas diffusion nature of the low-frequency stage of the electrode reaction. The gas diffusion layer thickness was estimated.     

Electronic spectra and electrochemistry of disubstituted 2,2′-bipyridinetetracarbonylmolybdenum complexes. Solvent and substituent effects

Electronic absorption spectra of cis-[Mo(CO)₄(n,n′-X₂-bipy)] (n = 4, X = NMe₂, NH₂, OMe, CMe₃, Me, H, Ph, CH:CHPh, CO₂H, Cl, CO₂Me, NO; n=5, X = Me, CO₂H) have been measured at ambient temperature in a variety of solvents of different polarity. Emission spectra from glasses containing the complexes at 77 K have also been measured. The influence of the substituent X on the spectroscopic properties is correlated with the Hammett parameters, σ_p (X) and σ_p⁺ (X). The effect of solvent is correlated with the Taft-Kamlet parameter, π^★, indicating charge redistribution along the permanent dipole axis of the complex. The oxidation and reduction potentials in solution are simply related to the electronic effect of the substituent group, X, and are relatively independent of the solvent. The influence of the metal on these properties is not significant.     

Product distribution in preparative scale electrolysis: Part VI. Competition between dimerization and first-order deactivation

The dependence of product distribution from the various experimental parameters (rates, concentration diffusion layer thickness, current density) is analyzed for a reaction scheme involving the competition between dimerization and first-order deactivation of the intermediate resulting from the first electron uptake (or removal). Two cases are considered, corresponding to the product of the first-order deactivation being either electroinactive or undergoing a further electron transfer at the electrode or in the solution. It is shown that the dimer yield is not very sensitive to the further fate of the deactivation product. It is in all cases a function of the competition parameter σ=k₁k₂^?3/2D^1/2 c⁰ δ^?1 in potentiostatic conditions and σ^Δ=k₁k₂^?3/2D^?1/2(i⁰/FS) in galvanostatic conditions (k₁, k₂ rate constants of the dimerization and deactivation reactions respectively; D diffusion coefficient; c⁰ concentration of substrate; δ diffusion layer thickness; (i⁰/S) current density). The reduction of CO₂ in DMF with competitive formation of oxalate and formate is taken as an example illustrating the theoretical analysis.     

Excitation of He—41 D-substates by He+- and Ne+-projectiles investigated by level-crossing techniques

Collisions of He⁺- and Ne⁺-projectiles with He at impact energies between 90 keV and 800 keV were investigated. Relative excitation cross sections for magnetic sublevels of He—4¹ D were determined using level-crossing techniques. Absolute excitation cross sections σ _m of the Zeeman-sublevels are given using He—4¹ D cross sections from earlier measurements. The results show strong variations of the cross sections σ₀ and σ_±1 with a quasi-oscillatory behaviour. σ_±2 is much smaller than σ₀ and σ_±1.     

Dielectric properties of films of Ag-ED20 epoxy nanocomposite synthesized in situ. Temperature dependence of direct current conductivity

The influence of silver myristate used as a precursor of silver nanoparticles on the direct current conductivity σ _dc of epoxy polymer within the concentration range of ≤0.8 wt % was investigated. The value of direct current conductivity was determined on the basis of analysis of the frequency dependence of complex permittivity within the frequency range of 10^?2–10⁵ Hz. The temperature dependence of σ _dc is composed of two regions. The dependence corresponds to the Vogel-Fulcher-Tammann empirical law σ _dc = σ _dc0exp{?DT ₀/(T-T ₀)} (where T ₀ is the Vogel temperature and D is the strength parameter) at temperatures higher than the glass transition temperature T _g. At the same time, T ₀ does not depend on the concentration of nanoparticles. The Arrhenius temperature dependence characterized by activation energy about 1.2 eV is observed at temperatures lower than T _g. The observed shape of the temperature dependence is related to the change in the mechanism of conductivity after “freezing” of ionic mobility at temperatures lower than T _g. The value of σ _dc is increased as the concentration of nanoparticles is raised within the temperature range of T > T _g. The obtained dependence of σ _dc on silver myristate concentration is similar to the root one, indicating the absence of percolation within the studied range of concentrations.     

Study of the Fermi doublet ν1 — 2ν2 in the Raman spectra of CO2 in different phases

The relation between the intensity ratio R and the frequency separation Δ of the Fermi doublet components ν₊ and ν₋ in the Raman spectra of CO₂ in dense gas, liquid, solid and aqueous solutions is used to establish the correct assignment of the levels to ν₁ and 2ν₂. The unperturbed fundamental ν⁰₁ is at higher frequency than 2ν⁰₂ in all the phases studied. The values of ν⁰₁ increase and of 2ν⁰₂ decrease with pressure. The values of W and K₁₂₂ are nearly constant for the dense gas, liquid and solid in the pressure range of 6–44 kbars, but decrease in the solid for pressures up to 100 kbars and also in aqueous solutions.     

Three-body association of CO+ and N2. The case for a chemical bond

Hamilton, Bierbaum and Leone recently reported a very efficient vibrational quenching of CO⁺ (v) by N₂, only about six collisions being required for quenching at 300 K. This is an exceedingly efficient quenching process in the light of recent systematic studies of diatomic molecular ion vibrational quenching. To probe further the CO⁺−N₂ interaction, the rate coefficient for three-body association of CO⁺ and N₂ with He as third body was measured and is very large, being 2.1 × 10⁻²⁹ cm⁶ s⁻¹ at 298 K and 1.8 × 10⁻²⁸ cm⁶ s⁻¹ at 80 K. Both the efficient quenching and the rapid association imply a strong interaction between CO⁺ and N₂, much stronger than the expected ≈ 0.2 eV electrostatic potential well depth. These experiments indicate a “chemical bonding” interaction between CO⁺ and N₂, with a well depth as large as 1 eV.     

Collision rotational transfers in NaH A1Σ+ by He,Ar or H2 (and in KH A1Σ+ by H2)

The total and relative rotational transfer cross sections σ_total and σ_Ji-Jf, by collisions of NaH A¹Σ with He, Ar or H₂, are measured from υ′ = 4 and υ′ = 11, J₁′ = 6. The σ_total increase as υ′ increases. They are similar for He and H₂ but much greater for Ar especially at large υ′. In NaH A¹Σ⁺ the bond goes from covalent to ionic as υ′ increases: σ_total is very sensitive to an attractive potential due to the interaction of the permanent electric dipole moment of the molecule with the polarizability of the atom (α_Ar = 11 au, α_He = 1.37 au). The σ_Ji-Jf decrease monotonously as |J_f-J_i| increases and may be fitted by a scaling law. The variation with ΔJ depends on the colliding gas but does not change appreciably with υ′: most of the transfers could take place on the repulsive part of the interaction potential, the shape of which would not depend on υ′.     

Carbon dioxide and nitrogen adsorption on porous copolymers of divinylbenzene and acrylic acid

Porous copolymers of divinylbenzene (DVB) and acrylic acid (AA) having DVB:AA ratios of 6:4, 8:2 and 9:1 were prepared following a distillation-precipitation method, using toluene as the porogenic agent. The materials thus obtained, which showed specific surface area in the range of 380–600 m² g^?1 and pore volume in the range of 0.14–0.18 cm³ g^?1, were investigated as possible adsorbents for CO₂ capture from the flue gas of coal-fired power stations. For that purpose, the isosteric heat of adsorption (and CO₂ adsorption capacity) was analysed from N₂ and CO₂ adsorption equilibrium isotherms obtained over a temperature range. For CO₂, q _st resulted to be in the range of 27–31 kJ mol^?1 (the highest value corresponding to the 6:4 sample), while for N₂ a value of q _st ≈ 12 kJ mol^?1 was obtained. Equilibrium adsorption capacity for CO₂ (at ambient temperature and pressure) showed the value of about 1.35 mmol g^?1. These results are discussed in the broader context of corresponding literature data for CO₂ capture using protonic zeolites.     

Complexation and abstraction channels in the Al + CO2 reaction

The AI + CO₂ reaction is studied in the gas phase at 296 K by laser-induced fluorescence monitoring of Al and AlO. Pressure dependence of the effective bimolecular rate constant in the range 10–600 Torr (Ar+CO₂) indicates a complex formation channel yielding a stable Al·CO₂ adduct. Observation of AlO confirms the presence of an abstraction channel. A simple chemical activation mechanism is used to interpret the pressure dependence of the effective bimolecular rate constant. The activation energy for Al·CO₂ complex formation is estimated at ⪢ 1.0 kcal mol⁻¹, and the binding energy is estimated at ⪢ 9 kcal mol⁻¹.     

Reactions of O with CO van der Waals molecules and clusters

The reaction of O(³ P) with COR _m clusters to produce electronically excited CO₂ was studied under molecular beam conditions. It was found that the spectrum of the chemiluminescence produced extended from the blue all the way to the near infrared. The dependence of the total emission intensity on stagnation pressure was investigated for (CO) _m as well as for COR _m , R=He, Ne, Ar, N₂, CO₂ and SO₂. The low pressure data indicate that small (CO) _m polymers are more efficient than clusters of CO with other species in inducing the chemiluminescent reaction. The larger CO-rare gas clusters, however, exhibited larger reaction cross-sections than those of the CO polymers. Rare gas clusters ofm≧5, on the other hand have successively smaller cross sections for reaction. The reactivity of the CO₂ and SO₂ clusters seems to peak at aboutm=1 and then decreases for larger species. An equilibrium model for cluster formation was proposed and it was found capable of explaining and simulating the experimental observations. Contrary to what was reported from afterglow experiments, no barrier for the reaction was detected.     

T−12-law of dc conductivity 1N Langmuir films

Measurements of dc conductivity of Cd-stearate multilayer films below room tenperature down to liquid nitrogen temperature have revealed the temperature dependence σ = σ₀ exp(?AT^{?$\text{1}\text{2}$}). This relation, together with the values of σ₀ and A, confirms the theoretical predictions for hopping conduction in a multilayer system associated with interface states.     

CO2-induced plasticization phenomena in glassy polymers

A typical effect of plasticization of glassy polymers in gas permeation is a minimum in the relationship between the permeability and the feed pressure. The pressure corresponding to the minimum is called the plasticization pressure. Plasticization phenomena significantly effect the membrane performance in, for example, CO₂/CH₄ separation processes. The polymer swells upon sorption of CO₂ accelerating the permeation of CH₄. As a consequence, the polymer membrane loses its selectivity. Fundamental understanding of the phenomenon is necessary to develop new concepts to prevent it.In this paper, CO₂-induced plasticization phenomena in 11 different glassy polymers are investigated by single gas permeation and sorption experiments. The main objective was to search for relationships between the plasticization pressure and the chemical structure or the physical properties of the polymer. No relationships were found with respect to the glass-transition temperature or fractional free volume. Furthermore, it was thought that polar groups of the polymer increase the tendency of a polymer to be plasticized because they may have dipolar interactions with the polarizable carbon dioxide molecules. But, no dependence of the plasticization pressure on the carbonyl or sulfone density of the polymers considered was observed. Instead, it was found that the polymers studied plasticized at the same critical CO₂ concentration of 36±7 cm³ (STP)/cm³ polymer. Depending on the polymer, different pressures (the plasticization pressures) are required to reach the critical concentration.     

Giant Hysteretic Sorption of CO2: In Situ Crystallographic Visualization of Guest Binding within a Breathing Framework at 298 K

A dynamic Zn^II‐MOF has been shown to exhibit extreme breathing behavior under gas pressure. The very narrow pore form of the activated framework opens up in the presence of carbon dioxide, thus making it a suitable material for CO₂ capture. Sorption of CO₂ at 298 K and relatively high pressure clearly shows a two‐step isotherm with giant hysteresis for the second step. In‐situ single‐crystal diffraction analysis was carried out under CO₂ gas pressure at 298 K using an environmental gas cell in order to visualize the interaction between CO₂ and the host framework. The results are well supported by pressure‐gradient differential scanning calorimetry (P‐DSC) and variable‐pressure powder X‐ray analysis. Theoretical calculations have been carried out in order to further back up the crystallographic data.     

Prediction of ortho substituent effect in alkaline hydrolysis of phenyl esters of substituted benzoic acids in aqueous acetonitrile

The second-order rate constants k for the alkaline hydrolysis of phenyl esters of meta-, para- and ortho-substituted benzoic acids, X-C₆H₄CO₂C₆H₅, in aqueous 50.9% acetonitrile have been measured spectrophotometrically at 25°C. The log k values for meta and para derivatives correlated well with the Hammett σ_m,p substituent constants. The log k values for ortho-substituted phenyl benzoates showed good correlations with the Charton equation, containing the inductive, σ_I, resonance, σ^○ _R, and steric, E _s ^B, and Charton υ substituent constants. For ortho derivatives the predicted (log k _X)_calc values were calculated with equation (log k _ortho)_calc = (log k ^H _AN)_exp + 0.059 + 2.19σ_I + 0.304σ^○ _R + 2.79E _s ^B ? 0.0164ΔEσ_I — 0.0854ΔEσ^○ _R, where DE is the solvent electrophilicity, ΔE = E _AN — E _H20 = ?5.84 for aqueous 50.9% acetonitrile. The predicted (log k _X)_calc values for phenyl ortho-, meta- and para-substituted benzoates in aqueous 50.9% acetonitrile at 25°C precisely coincided with the experimental log k values determined in the present work. The substituent effects from the benzoyl moiety and aryl moiety were compared by correlating the log k values for the alkaline hydrolysis of phenyl esters of substituted benzoic acids, X-C₆H₄CO₂C₆H₅, in various media with the corresponding log k values for substituted phenyl benzoates, C₆H₅CO₂C₆H₄-X.     

CS(lav) and computational study of degeneracy averaged differerential cross sections and Δm-integral cross sections: Hez.sbndCO,HDz.sbnd

CC and l-average CS calculations of degeneracy averaged differential cross sections and Δm-integral cross sections have been performed for Hez.sbndCO at E = 60 cm^?1 and E = 80 cm^?1, for HDz.sbndNe at E = 254 cm^?1, and for Hez.sbndH₂ at E = 1520 cm^?1. The l_avz.sbndCS degeneracy averaged differential cross sections are generally in good agreement with the CC cross sections. The previously observed shifts in the diffraction oscillations for odd rotationally inelastic transitions for Hez.sbndCO and HDz.sbndNe do not occur due to proper phase choice and l? = l_av choice rather than l? = 1 or l′. The l_avz.sbndCS approximation gives reliable results for most Δm-integral cross sections except for those σ_cs(jm, jm′) cross sections for which the CC cross sections σ(jm;jm′) and σ(jm′;jm) differ by a large amount.     

Effect of various types of equations of state for prediction of simple gas hydrate formation with or without the presence of kinetic inhibitors in a flow mini-loop apparatus

This paper compares the effects of using various types of equations of state (PR,¹ SRK,² ER,³ PT⁴ and VPT⁵) on the calculated driving force and rate of gas consumption based on the Kashchiev and Firoozabadi model for simple gas hydrate formation for methane, carbon dioxide, propane and iso-butane with experimental data points obtained in a flow mini-loop apparatus with or without the presence of kinetic inhibitors at various pressures and specified temperatures. For this purpose, a laboratory flow mini-loop apparatus was set up to measure gas consumption rate when a hydrate forming substance (such as C₁, C₃, CO₂ and i-C₄) is contacted with water in the presence or absence of dissolved inhibitor under suitable temperature and pressure conditions. In each experiment, a water blend saturated with pure gas is circulated up to a required pressure. Pressure is maintained at a constant value during experimental runs by means of the required gas make-up. The total average absolute deviation was found to be 15.4%, 16.3%, 15.8%, 17.8% and 17.4% for the PR, ER, SRK, PT and VPT equations of state for calculating gas consumption in simple gas hydrate formation with or without the presence of kinetic hydrate inhibitors, respectively. Comparison results between the calculated and experimental data points of gas consumption were obtained in flow loop indicate that the PR and ER equations of state have lower errors than the SRK, VPT and PT equations of state for this model.     

Non-3d metal modulated zinc imidazolate frameworks for CO2 cycloaddition in simulated flue gas under ambient condition

Cycloaddition of CO₂ and epoxide into cyclic carbonate is one of the most efficient ways for CO₂ conversion with 100% atom-utilization. Metal–organic frameworks are a kind of potential heterogeneous catalysts, however, high temperature, high pressure, and high-purity CO₂ are still required for the reaction. Here, we report two new Zn(II) imidazolate frameworks incoporating MoO₄^2– or WO₄^2– units, which can catalyse cycloaddition of CO₂ and epichlorohydrin at room temperature and atomospheric pressure, giving 95% yield after 24 h in pure CO₂ and 98% yield after 48 h in simulated flue gas (15% CO₂ + 85% N₂), respectively. For comparison, the analogic Zn(II) imidazolate framework MAF-6 without non-3d metal oxide units showed 71% and 33% yields under the same conditions, respectively. The insightful modulation mechanisms of the MoO₄^2– unit in optimizing the electronic structure of Zn(II) centre, facilitating the rate-determined ring opening process, and minimizing the reaction activation energy, were revealed by X-ray photoelectron spectroscopy, temperature programmed desorption and computational calculations.     

A method for obtaining potential parameters for helium from T1 measurements

The temperature dependence of T₁ for ³He gas in the range 0–4°K is calculated for a Lennard-Jones (12,6) potential. The relaxation of the nuclear spins is assumed to be due to a dipolar interaction between the nuclei. A minimum value in the relaxation time, T_1,min, is found to occur at a temperature denoted by T_min. By repeating the calculation for different pairs of values of the potential parameters ? and σ, we have found that for a density of 10^?2 g/cm³,σ²T_min = 13.0?1.12 × 10³ ?σ², T_1,min/σ²(T_min)^{$\text{1}\text{2}$} = 17.4?6.56 × 10² ?σ², with ?, σ, T_min and T_1,min in eV, Å, °K and minutes, respectively. From measurements of T_min and T_1,min, ? and σ can be determined.     

The UV absorption spectrum of the CCl3 radical and the kinetics of its mutual combination reaction from 253 to 623 K

The UV absorption spectrum and the kinetics of the self combination reaction of the CCl₃ radical were studied by flash photolysis in the temperature range 253–623 K. Experiments were performed at the atmospheric pressure, except for a few runs at the highest temperatures, which were performed between 30 and 760 torr. CCl₃ radicals were generated by flash photolysis of molecular chlorine in the presence of chloroform. The UV spectrum exhibits a strong unstructured band between 195 and 260 nm with a maximum at 211 ± 2 nm. The absorption cross section, measured relative to σ(HO₂), is σ(CCl₃) = (1.45 ± 0.35) × 10^?17 cm² molecule^?1 at the maximum. This value takes into account the uncertainty in σ(HO₂) which was taken equal to (4.9 ± 0.7) × 10^?18 cm² molecule^?1. The absolute rate constant for the CCl₃ mutual combination was determined by computer simulation of the transient decays. The rate constant, which exhibits a slight negative temperature coefficient, can be expressed as: The study of the pressure dependence showed that only a slight fall-off behavior could be observed at the highest temperature (623 K). This result was corroborated by RRKM calculations which showed that the rate constant is at the high pressure limit under most experimental conditions below 600 K.