Potentials of Silver and Gold Electrodes of ZrO2-Based Cells in N2+ O2+ CO2+ CO Gas Mixtures

Steady-state electrode potentials in cells with a ZrO₂+ 10 mol % Y₂O₃electrolyte are measured at 400 to 500°C in nonequilibrium N₂+ O₂+ CO₂+ CO gas mixtures containing 0–3 and 0–10 vol % of CO and O₂, respectively. In CO-free mixtures, the potentials obey the Nernst equation. The CO-caused deviation of the potential from its equilibrium value depends on the O₂content and temperature and is due mainly to the CO adsorption at electrodes.     

Potentials of Oxide Electrodes in Cells with a Zirconium Dioxide-Based Electrolyte in Mixtures of Nitrogen,Oxygen, Carbon Dioxide,and Carbon Monoxide Gases

Measurements of steady-state potentials of various electrodes made of oxide compositions are performed in cells containing electrolyte ZrO₂ + 10 mol % Y₂O₃ at a temperature of 773 K in nonequilibrium gas mixtures N₂ + O₂ + 20 vol % CO₂ + CO, with variable CO (0.1–5 vol %) and O₂ (0.5–10 vol %) contents. After adding CO into a gas phase, potentials of all electrodes shift, to one degree or another. The shift is substantially affected by the O₂ content. The electrochemical systems under study are of some interest for analyzing partial pressures of CO in gas mixtures. The discovered effect must be taken into account when employing such electrodes for the determination of partial concentrations of other components of a gas mixture, for example, oxygen.     

Catalytic Removal of NOx from Gas Mixtures Simulating Emissions from the Combustion of Biofuels

The activity of knitted silica-fibre supported Pd, Pt, Pt-Ni, Pd-Ni and Pd-Pt-Ni catalysts as well as Pd based H-ZSM-5 and H-ZSM-35 catalysts was studied in the conversion of gas mixtures containing 200 ppm CH₄, 2500 ppm CO, 500 ppm pyridine (or 500 ppm NO), 10 vol.% O₂ (or 0.155 vol.% O₂), 12 vol.% CO₂, 12 vol.% H₂O, balanced with He at GHSV of 60000 h^–1. Pyridine was found to inhibit both CO and CH₄ oxidation. IR studies indicated that NO adsorbed on Pd²⁺ is the principal adsorbed species on the Pd/HZSM-5 catalyst.     

Sensitivity of Semiconductor Gas Sensors to Hydrogen and Oxygen in an Inert Gas Atmosphere

Semiconductor gas sensors with nine types of gas-sensing films were prepared and their sensitivity for hydrogen and oxygen in binary and ternary gas mixtures containing nitrogen in concentrations of 0–4 and 0–8 vol %, respectively was studied. The sensor temperature was varied from 200 to 500°C. Sensors based on an In₂O₃+ Al₂O₃(30 : 70) composite with platinum contact areas exhibited the best metrological and performance characteristics. The resistance of sensors heated to an optimum temperature of 400°C was measured as a function of the test gas concentration. In principle, the concentrations of the components in nitrogen can be determined to within 5 rel % with the use of the above functions.     

On the analysis of CO2, H2- and CO,H2-mixtures by water-gas potentiometry with solid electrolyte cells

The potentiometric analysis of CO₂, H₂ and CO, H₂O-mixtures using oxide ion-conducting solid electrolytes requires the adjustment of the water-gas equilibrium without side reactions in the high-temperature galvanic cell. Conventional cell designs suitable for the analysis of H₂, H₂O and CO, CO₂-mixtures are not applicable due to the insufficient gas residence times in the cells and the insufficient catalytical activity of the platinum electrodes. Solid electrolyte cells have to be modified by integrating of suitable catalysts. Under optimized conditions of gas velocity and cell temperature both gas systems can be analyzed only by measuring the cell tension U (=–emf) and temperature in the favorized temperature range around 813°C. Here systematical errors of the component ratio or the mole fraction were smaller than 6%. Several fundamental requirements for the application of catalysts in solid electrolyte cells for the analysis of reactive water-gas mixtures are pointed out.     

Reactions of (CO2)2+ and (CO)2+ association ions

The reactons of (CO₂)₂⁺ and (CO)₂⁺ with various additives have been investigated using the NBS high-pressure photoionization mass spectrometer at total pressures of 0.4–1.0 torr of either CO₂ or CO. The additives include CH₄, CD₄, C₂H₂, O₂, H₂O, ^15,14N₂O, and CO in both CO₂ and ¹³CO₂. Second- and third-order rate coefficients based on an ambipolar diffusion model are reported for 25 separate reaction pairs at 295°K, as well as sequential cationic reaction mechanisms. An approximate value of 225 ± 3 kcal/mol (941 ± 13 kJ/mol) was derived for ΔH_f (CO)₂⁺ based on the kinetics observed in various CO-additive mixtures. Some projections regarding the utility of the data under other conditions are also included.     

An Artificial Electrode/Electrolyte Interface for CO2 Electroreduction by Cation Surfactant Self-Assembly

In this work, an artificial electrode/electrolyte (E/E) interface, made by coating the electrode surface with a quaternary ammonium cation (R₄N⁺) surfactant, was successfully developed, leading to a change in the CO₂ reduction reaction (CO₂RR) pathway. This artificial E/E interface, with high CO₂ permeability, promotes CO₂ transportation and hydrogenation, as well as suppresses the hydrogen evolution reaction (HER). Linear and branched surfactants facilitated formic acid and CO production, respectively. Molecular dynamics simulations show that the artificial interface provided a facile CO₂ diffusion pathway. Moreover, density-functional theory (DFT) calculations revealed the stabilization of the key intermediate, OCHO*, through interactions with R₄N⁺. This strategy might also be applicable to other electrocatalytic reactions where gas consumption is involved.     

Diagnostics of a Radio-Frequency Plasma Expanding Through a Nozzle (PETN) at Low Pressure

The diagnostics of the radio-frequency (induction mode) plasma expanded through a nozzle (PETN) at low pressures (100–1000 Pa) was performed by on-line optical emission spectroscopy (OES) and on line quadrupole mass spectrometry (QMS). The OES was used for evaluating the electronic, vibrational, and rotational temperatures (T_e, T_v, and T_r) along the plasma reactor before and after the nozzle. The PETN gas mixtures analyzed were Ar+N₂, Ar+CO, and Ar+O₂with an addition of 1 vol.% N₂to the last two gas mixtures. For the same conditions in the PETN the values of T_e, T_v, and T_r were found to be different for the different gas mixtures and related to the depopulation of excited N ₂ ⁺ by oxygen atoms. Moreover the Ar+O₂PETN aqueous solutions of lanthanum and manganese nitrates were nebulized for the deposition of LaMnO₃perovskite. The QMS, in real time, measuring the mass species formed before and after the nozzle, explained the reasons in the different values of T_e, T_v, and T_r for the three gas mixtures as well as for the formation of oxides in the PETN from the aqueous nitrate solutions.     

Steady-state electrode potentials of solid-electrolyte cells in reducing chemically nonequilibrium gas mixtures

The paper studies the steady-state potential response of the electrodes of solid-electrolyte cells with ZrO₂ + 9 mol % Y₂O₃ in reducing nonequilibrium gas mixtures of N₂ + H₂ + H₂O + O₂ with a low content of O₂ and in the mixtures of CH₄ + CO₂ + CO with a low content of CO, in the temperature range of 450–900°C. The dependences of potentials of the electrodes of different materials on the temperature and composition of gas mixtures were measured. The results were compared with the values of potentials in corresponding mixtures after chemical equilibrium was established. Characteristic temperature were determined, above which the electrodes feature a potential corresponding to chemically equilibrium mixtures.     

Interactions of vibrationally excited CO2 with oxygen and sulfur atoms

The classical-path method has been used in calculations on O+CO₂ CO+ O₂ and S+CO₂ CO+SO for vibrational-translational disequilibrium. The vibrational-energy localization in various modes in CO₂ affects the reaction cross section and rate constant. The energy distributions in the products have been calculated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 428–434, July–August, 1988.     

CN chemiluminescence in N2 + CH4 Flowing afterglow at low temperatures

The spectra of flowing microwave post-discharge excited in N₂ and N₂ + CH₄(N₂ + C₂H₂) gas mixtures have been studied at low temperature (77 K). The molecular spectra of CN emitted by the collision-induced N + C and N + CH chemiluminescent reactions in the low-temperature afterglow system have been thoroughly investigated. The intensity of different CN (B²⁺-X²⁺) vibrational bands is very sensitive to low hydrocarbon concentration in nitrogen used as the working gas. Detection of hydrocarbon species has been demonstrated from concentrations of CH₄ and C₂H₂ in N₂ greater than 10¹⁰ molecules · cm^–3.     

A photoacoustic study of the collisional deactivation of CO2 by N2, CO and O2 between 160 and 375 K

A photoacoustic method is used under such experimental conditions that the (01¹0) level of CO₂ gas is not in equilibrium with the other vibrational levels. The rate constants κ′₁₀ characterizing the CO₂ (01¹0) collisional deactivation by N₂, CO and O₂ are measured directly.     

Heterogeneous recombination of O + CO on solid CO2 at 77 K

Heterogeneous recombination of O + CO → CO₂ over a solid CO₂ surface at 77 K was investigated. A modified discharge flow setup was used to generate low O atom concentrations by the reaction N + NO → N₂ + O(³P). The O atom concentrations were measured upstream and downstream of the solid CO₂ substrate using resonance fluorescence by monitoring the unresolved 130.3 nm triplet transition ³S₁ ? ³P_2,1,0 at the two fixed points. CO₂ formed was determined by measuring the β activity from C¹⁴O₂ produced from CO containing C¹⁴O as a reactant gas. The CO₂ formation was found to be first order in CO and independent of O atom concentration over the entire range of 4.3 × 10¹² to 1.9 × 10¹⁴ cm^?3 and 1.2 × 10¹¹ to 5.6 × 10¹² cm^?3 for CO and O respectively. The first order recombination coefficient, λ_CO was found to be 1.4 (±.38) × 10^?5.     

Thin Films Deposition from Hexamethyldisiloxane and Hexamethyldisilazane under Dielectric-Barrier Discharge (DBD) Conditions

Hexamethyldisiloxane (HMDSO) and hexamethyldisilazane (HMDSN) were used as organosilicon reagents for PE-CVD of thin films under filamentary barrier-discharge conditions at atmospheric pressure. Efficient discharges were obtained in the region of moderate frequencies (5 kHz). The following mixtures of organosilicon reagents with carrier gas and oxidants or ammonia were investigated: HMDSO+Ar, HMDSO+N₂, HMDSO+O₂+Ar, HMDSO+N₂O+Ar, and HMDSN+NH₃+N₂. Under such conditions HMDSO was converted to produce thin films (10–1000 nm) of silicon oxide, generally containing admixtures of residual organic content (Si—CH_n and Si—H groups). The films deposited from HMDSN+NH₃+N₂ contained silicon, nitrogen and oxygen.     

Rate Determination of the CO2* Chemiluminescence Reaction CO + O + M CO2* + M

Electronically excited carbon dioxide (CO₂*) is known for its broadband emission, and its detection can lead to valuable information; however, owing to its broadband characteristics, CO₂* is difficult to isolate experimentally, and its chemical kinetics are not well known. Although numerous works have monitored CO₂* chemiluminescence, a full kinetic scheme for the excited species has yet to be developed. To this end, a series of shock‐tube experiments was performed in H₂‐N₂O‐CO mixtures highly diluted in argon at conditions where emission from CO₂* could be isolated and monitored. These results were used to evaluate the kinetics of CO₂*, in particular the main CO₂* formation reaction CO + O + M CO₂* + M (R1). Based on collision theory, the quenching chemistry of CO₂* was estimated for 11 collision partners. The final mechanism developed for CO₂* consists of 14 reactions and 13 species. The rate for (R1) was determined to within about ±60% using low‐pressure experiments performed in five different (H₂‐)N₂O‐CO‐Ar mixtures, as follows: where R is the universal gas constant in cal/mol‐K and T is the temperature in K. Final mechanism predictions were compared with experiments at low and high pressures, with good agreement at both conditions for the temperature dependence of the peak CO₂* and the CO₂* species time histories. Comparisons were also made with previous experiments in methane–oxygen mixtures, where there was slight overprediction of CO₂* experimental trends, but with the results otherwise showing a dramatic improvement over an earlier mechanism. Experimental results and model predictions were also compared with past literature rates for CO₂*, with good agreement for peak CO₂* trends and slight discrepancies in CO₂* species time histories. Overall, the ability of the CO₂* mechanism developed in this work to reproduce a range of experimental trends represents an important improvement over the existing knowledge base on chemiluminescence chemistry.     

Electrochemical reduction of CO2 with high current density in a CO2 + methanol medium II. CO formation promoted by tetrabutylammonium cation

The cation of the supporting electrolyte was found to play an important role in the electrochemical reduction of highly concentrated CO₂ in a CO₂ + methanol medium. Electroreduction of CO₂ with tetrabutylammonium (TBA) salts yielded CO as the main product, while methyl formate was predominantly formed when lithium salts were used as supporting electrolytes. The latter supporting electrolytes showed a higher overvoltage than the former. When TBA salt was used, the reduction of CO₂ was catalysed by TBA ion to yield CO^−.₂. This intermediate may be stabilized by forming an ion pair, {TBA⁺---CO^−.₂}, or by being adsorbed on the electrode surface as CO^−._2ad. Then CO^−.₂ reacts with CO₂ to produce CO. The hydrophobic atmosphere at the electrode provided by TBA ion may be adequate for CO production. Lithium ion, on the other hand, suppressed the reduction of CO₂.     

Efficient CO2 Removal for Ultra‐Pure CO Production by Two Hybrid Ultramicroporous Materials

Removal of CO₂ from CO gas mixtures is a necessary but challenging step during production of ultra‐pure CO as processed from either steam reforming of hydrocarbons or CO₂ reduction. Herein, two hybrid ultramicroporous materials (HUMs), SIFSIX‐3‐Ni and TIFSIX‐2‐Cu‐i , which are known to exhibit strong affinity for CO₂, were examined with respect to their performance for this separation. The single‐gas CO sorption isotherms of these HUMs were measured for the first time and are indicative of weak affinity for CO and benchmark CO₂/CO selectivity (>4000 for SIFSIX‐3‐Ni ). This prompted us to conduct dynamic breakthrough experiments and compare performance with other porous materials. Ultra‐pure CO (99.99 %) was thereby obtained from CO gas mixtures containing both trace (1 %) and bulk (50 %) levels of CO₂ in a one‐step physisorption‐based separation process.     

Selective methanation of CO in the presence of CO<Subscript>2</Subscript> in hydrogen-containing mixtures on nickel catalysts

The screening of commercial nickel catalysts for methanation and a series of nickel catalysts supported on CeO₂, γ-Al₂O₃, and ZrO₂ in the reaction of selective CO methanation in the presence of CO₂ in hydrogen-containing mixtures (1.5 vol % CO, 20 vol % CO₂, 10 vol % H₂O, and the balance H₂) was performed at the flow rate WHSV = 26000 cm³ (g Cat)⁻¹ h⁻¹. It was found that commercial catalytic systems like NKM-2A and NKM-4A (NIAP-07-02) were insufficiently effective for the selective removal of CO to a level of <100 ppm. The most promising catalyst is 2 wt % Ni/CeO₂. This catalyst decreased the concentration of CO from 1.5 vol % to 100 ppm in the presence of 20 vol % CO₂ in the temperature range of 280–360°C at a selectivity of >40%, and it retained its activity even after contact with air. The minimum outlet CO concentration of 10 ppm at 80% selectivity on a 2 wt % Ni/CeO₂ catalyst was reached at a temperature of 300°C.     

The CO2 Reforming of Natural Gas in a Pulsed Corona Discharge Reactor

The conversion of CO ₂ and (CH ₄+CO ₂ ) mixtures to CO, at room temperature and atmospheric pressure conditions, in pulsed corona discharges, was investigated. Conversion of pure CO ₂ was 16.8% at 10 cm ³ -min ^–1 flow rate, which corresponds to 75 mol-min ^–1 rate of conversion. The CO ₂ conversion was improved to 38% (85 mol-min ^–1 by feeding the reactor with CH ₄+CO ₂ gas mixture (1:1 ratio), simultaneously with CH ₄ conversion of 46% (102.7 mol-min ^–1 ) at 10 cm ³ -min ^–1 flow rate of feed gases and 9 W power conditions. Rate of CO production is increased from 110 to 180 mol-min ^–1 with the variation of feed gas (CH ₄+CO ₂ mixture, 1:1 ratio) flow rate from 10 to 40 cm ³ -min ^–1 at 9W, which corresponds to energy efficiency of 2.5 to 4.1%. Highest energy yield of 25 g/kWh for CH ₄ conversion, 29 g/kWh for CO ₂ conversion, and 33 g/kWh for CO production were achieved.