Vibration—vibration energy exchange between carbon monoxide and carbon dioxide

Measurements have been made on the vibration—vibration (V—V) energy exchange rate between carbon monoxide and carbon dioxide in the temperature range 180 to 345 K. A steady-state vibrational fluorecence quenching technique was used in conjunction with an open flow gas system. Vibrational excitation of the carbon monoxide was accomplished by absorption of infrared radiation from prospane—oxygen flames. The measured rate constant for the process CO* (υ = 1) + CO₂ → CO + CO^*₂(001) increased linearly with temperature, and after correction for the V—V exchange rate fo the back reaction, the rate constant has a value of (2.2 ± 0.3) × 10³ torr^?1 s^?1 at 296 K. The data are compared to results at highest temperatures and to available theoretical calculations.     

An investigation of the catalytic performance of Fe–Mn/Al2O3 nanocatalyst for light olefins production using RSM method and kinetic study

The Fe–Mn/Al₂O₃ nanocatalysts were manufactured via the sol-gel procedure and were evaluated for Fischer–Tropsch synthesis. The impact of different operational parameters of T, P, and H₂/CO ratio on the catalytic performance for light olefins production has been studied using response surface methodology (RSM). Furthermore, the optimization and modeling of selected responses were also carried out via RSM and historical data design type of DOE; and the best process conditions were found to be T = 365°C, H₂/CO = 1.50, and P = 1.50 bar. The mechanism of CO hydrogenation reaction over the Fe–Mn/Al₂O₃ nanocatalysts was also investigated using the non-linear regression method. It was found that the mechanism of the CO hydrogenation reaction is based on the Eley–Rideal type and the best-fitted equation for this mechanism was found to be −r_CO = KP_COP_H2/1+αP_CO. The obtained value of activation energy (85.20 kJ mol⁻¹) affirmed the absence of internal mass transfer limitations. The physico-chemical properties of the samples were investigated by various techniques of XRD, BET, TPR, TGA, and DSC.     

A Stopped-flow Study on the Kinetics and Mechanism of CO2 Uptake by the cis-[Cr(1,10-phenanthroline)2(OH2)2]3+ Complex Ion

The kinetics of the reaction between gaseous CO₂ and the cis-[Cr(phen)₂(OH₂)₂]³⁺ ion leading to the formation of the carbonato complex ion, have been studied over the pH and temperature ranges: 3 < pH < 6 and 5 < T < 25 °C, respectively, at a constant ionic strength of 1 m (NaClO₄). Investigations were carried out using the stopped-flow spectrophotometry technique in the UV–Vis range: 340–700 nm. The major reactant species in the pH range studied was cis-[Cr(phen)₂(OH)(OH₂)]²⁺ ion, which underwent reaction with CO₂ to form cis-[Cr(phen)₂(OH₂)(HCO₃)]²⁺ ion. Subsequently, slower ring closure of the latter species to form the bidentate carbonato chelate was observed. The possible mechanism has been discussed and the activation parameters ΔH^† and ΔS^† were also determined for the reaction studied.     

Cluster quantum chemical study of the interaction between a carbon monoxide molecule and a zinc oxide surface

This paper gives the results of quantum chemical MINDO/3 calculations of carbon monoxide adsorption on the ZnO polar (0001) surface. The energetically most favorable one-center adsorption of carbon monoxide on the ZnO (0001) surface occurs by the electron density transfer from the lone electron pair of CO carbon to the vacant orbital of the Zn _3C ²⁺ cation. The calculated heat of CO adsorption, dependent on the type of covering, and the stretching frequency υ_CO are in good agreement with the available experimental data. Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Ruhr University, Bochum, Germany. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 1, pp. 12–16, January–February, 1994. Translated by L. Smolina     

The rate constant of the reaction HO2 + COCO2 + OH

The high-temperature oxidation of formaldehyde in the presence of carbon monoxide was investigated to determine the rate constant of the reaction HO₂ + CO ? CO₂ + OH (10). In the temperature range of 878–952°K from the initial parts of the kinetic curves of the HO₂ radicals and CO₂ accumulation at small extents of the reaction, when the quantity of the reacted formaldehyde does not exceed 10%, it was determined that the rate constant k₁₀ is A computer program was used to solve the system of differential equations which correspond to the high-temperature oxidation of formaldehyde in the presence of carbon monoxide. The computation confirmed the experimental results. Also discussed are existing experimental data related to the reaction of HO₂ with CO.     

Determination of the mechanism of the oxidation of the trichloromethyl radical by the photolysis of chloral in the presence of oxygen

The photooxidation of chloral was studied by infrared spectroscopy under steady-state conditions with irradiation of a blackblue fluorescent lamp (300 nm < λ < 400 nm, λ_max = 360 nm) at 296 ± 2 K. The products were hydrogen chloride, carbon monoxide, carbon dioxide, and phosgen. The kinetic results reveal that the reaction proceeds via chain reaction of the Cl atom: The results lead to the conclusion that mechanism (B) is confirmed to be more likely than mechanism (A), which was favored at one time by Heicklen for the mechanism of the oxidation of trichloromethyl radicals by oxygen molecules: The ratio of the initial rates of CO and CO₂ formation gave k₇/k₆ = 4.23M^?1, and the lower limit of reaction (5) was found to be 3.7 × 10⁸M^?1 sec^?1.     

Photoreduction of carbon dioxide by hydrogen and methane

Zirconium oxide is active for photoreduction of gaseous carbon dioxide to carbon monoxide with hydrogen. A stable surface species arises under the photoreduction of CO₂ on zirconium oxide, and it is identified as surface formate by infrared spectroscopy. Adsorbed CO₂ is converted to formate by photoreaction with hydrogen. The surface formate is a true reaction intermediate since CO is formed by the photoreaction of formate and CO₂; surface formate works as a reductant of carbon dioxide to yield carbon monoxide. The dependence on the wavelength of irradiation light shows that a bulk ZrO₂ is not a photoactive species. When ZrO₂ adsorbs CO₂ a new band appears in photoluminescence excitation spectrum. The photoactive species in the reaction that CO₂+H₂ yields HCOO⁻ is presumably formed by the adsorption of CO₂ on ZrO₂ surface. Hydrogen molecules play a role to supply an atomic hydrogen. Therefore, methane molecules can also be used as a reductant of carbon dioxide.     

Vibrational energy storage in high pressure mixtures of diatomic molecules

CO/N₂, CO/Ar/O₂, and CO/N₂/O₂ gas mixtures are optically pumped using a continuous wave CO laser. Carbon monoxide molecules absorb the laser radiation and transfer energy to nitrogen and oxygen by vibration–vibration energy exchange. Infrared emission and spontaneous Raman spectroscopy are used for diagnostics of optically pumped gases. The experiments demonstrate that strong vibrational disequilibrium can be sustained in diatomic gas mixtures at pressures up to 1 atm, with only a few Watts laser power available. At these conditions, measured first level vibrational temperatures of diatomic species are in the range T_V=1900–2300 K for N₂, T_V=2600–3800 K for CO, and T_V=2200–2800 K for O₂. The translational–rotational temperature of the gases does not exceed T=700 K. Line-of-sight averaged CO vibrational level populations up to v=40 are inferred from infrared emission spectra. Vibrational level populations of CO (v=0–8), N₂ (v=0–4), and O₂ (v=0–8) near the axis of the focused CO laser beam are inferred from the Raman spectra of these species. The results demonstrate a possibility of sustaining stable nonequilibrium plasmas in atmospheric pressure air seeded with a few percent of carbon monoxide. The obtained experimental data are compared with modeling calculations that incorporate both major processes of molecular energy transfer and diffusion of vibrationally excited species across the spatially nonuniform excitation region, showing reasonably good agreement.     

Density-functional theory calculation on the nitrogen oxide reduction reaction with carbon monoxide on a titanium dioxide nanocluster

The density functional theory was used for simulation of the NO reduction reaction with carbon monoxide on a reduced Ti₈O₁₅ nanocluster. The reaction proceeds on oxygen vacancies formed via the removal of terminal or bridging O atoms. In the case of adsorption of two NO molecules of such sites, a stable adsorption complex with the bidentate ligand ‥ONNO is produced. When a CO molecule approaches one of the O atoms of this cycle, the following exothermic reaction yielding N₂ and CO₂ adsorbed on the Ti₈O₁₆ cluster takes place: 2NO+ CO + Ti₈O₁₅ → N₂+ Ti₈O₁₆ · CO₂. The proposed model of the reaction agrees well with experimental data.     

Resolution of the mechanism of CO electrooxidation on steady state and evaluation of the kinetic parameters for Pt and Ru electrodes

The carbon monoxide oxidation reaction (COOR) was studied on steady-state conditions by chronoamperometry on polycrystalline smooth platinum and ruthenium rotating disc electrodes in CO-saturated acid solution. The chronoamperometric response did not show current oscillations and therefore the current density (j) vs. overpotential (η) curves on steady state could be obtained. In order to interpret these results, kinetic expressions were derived starting from the mechanism proposed by S. Gilman, which considers two adsorbed reaction intermediates, carbon monoxide (CO_ad) and hydroxyl (OH_ad). Analytical expressions as a function of overpotential for the current density, the surface coverage of the adsorbed species (θ _CO and θ _OH) and the CO and CO₂ pressures at the electrode surface on steady state were obtained. This set of equations was used for the correlation of the experimental polarization curves and the evaluation of the corresponding kinetic parameters. From these values, the dependences of the surface coverage of the adsorbed intermediates on overpotential were simulated, as well as those of the partial pressure of CO and CO₂. Thus, it was demonstrated that the Gilman’s mechanism accurately describes the experimental results on steady state of the COOR on these metals.     

Spectral Investigation of the Interaction of Carbon Monoxide and Dioxygen with Low-Temperature Sublimates of Co(II) meso-Tetraphenylporphyrinate: Evidences for Oxidative Catalysis

The interaction of carbon monoxide and dioxygen with low-temperature (T= 77 K) sublimates of cobalt(II) meso-tetraphenylporphyrinate (CoTPP) is studied by IR spectroscopy using isotopically labeled compounds (¹³CO and ¹⁸O₂). The obtained data confirm the coordination of CO and O₂with the formation of axial complexes CoTPP · L (L = O₂, CO) and the mixed complex O₂· CoTPP · CO. The heating of the complex containing CO and O₂to 150 K leads to the appearance of lines in the IR spectrum corresponding to valence asymmetric (_asOCO) and degenerated deformation (OCO) vibrations of carbon dioxide. This is evidence for the oxidation of CO. The evacuation of CO₂at a higher, but still low, temperature and the addition of a new portion of CO and O₂mixture lead to the formation of new portions of CO₂. This demonstrates the catalytic character of the process. Only low-temperature sublimates have catalytic properties. Sublimates of CoTPP obtained on the surface at room or higher temperature demonstrate neither catalytic activity nor the ability to coordinate any amount of CO and O₂sufficient for the detection by spectroscopy.     

Partially Oxidized Palladium Nanodots for Enhanced Electrocatalytic Carbon Dioxide Reduction

Here we report a partially oxidized palladium nanodot (Pd/PdO_x) catalyst with a diameter of around 4.5 nm. In aqueous CO₂‐saturated 0.5 m KHCO₃, the catalyst displays a Faradaic efficiency (FE) of 90 % at −0.55 V vs. reversible hydrogen electrode (RHE) for carbon monoxide (CO) production, and the activity can be retained for at least 24 h. The improved catalytic activity can be attributed to the strong adsorption of CO₂^.− intermediate on the Pd/PdO_x electrode, wherein the presence of Pd²⁺ during the electroreduction reaction of CO₂ may play an important role in accelerating the carbon dioxide reduction reaction (CO₂RR). This study explores the catalytic mechanism of a partially oxidized nanostructured Pd electrocatalyst and provides new opportunities for improving the CO₂RR performance of metal systems.     

Thermal decomposition of ethane

The decomposition of C₂H₆ in Ar was studied by laser-absorption and laser-schlieren measurements of the reaction rate behind incident shock waves with 1300 < T < 2500°K and 1.1 < ρ < 4.4 × 10^?6 mol/cm³. The experimental profiles were parameterized by suitable measures of reaction progress. Computer simulations using a 14-reaction mechanism were used to compare assumptions about rate constant expressions with the experimental parameters and to investigate the sensitivity of computed parameters to these assumptions. A rate constant expression k(cm³/mol˙sec) = 2 × 10¹¹¹ T^?25.26 exp(?80 320/T) was found for the primary dissociation step C₂H₆ + M ? CH₃ + CH₃ + M under the conditions studied; no difference in rate was discernable between M ? Ar and M ? C₂H₆. Rate constant expressions found to be suitable for the remaining reactions of the mechanism, to some of which the computed parameters were sensitive, were in accord with previous proposals. Our results and results from earlier investigations of the primary decomposition reaction, in both forward and reverse directions, were extrapolated, using RRK methods, to obtain low-pressure limiting rate constants and found to be concordant.     

Catalytic Reduction of CN−, CO,and CO2 by Nitrogenase Cofactors in Lanthanide‐Driven Reactions

Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN⁻), carbon monoxide (CO), and carbon dioxide (CO₂) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI₂) and 2,6‐lutidinium triflate (Lut‐H) are employed as a reductant and a proton source, respectively. Driven by SmI₂, the cofactors catalytically reduce CN⁻ or CO to C₁–C₄ hydrocarbons, and CO₂ to CO and C₁–C₃ hydrocarbons. The C C coupling from CO₂ indicates a unique Fischer–Tropsch‐like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN⁻, CO, and CO₂ by isolated cofactors suggests the possibility to develop nitrogenase‐based electrocatalysts for the production of hydrocarbons from these carbon‐containing compounds.     

Catalytic Reduction of CN−, CO,and CO2 by Nitrogenase Cofactors in Lanthanide‐Driven Reactions

Nitrogenase cofactors can be extracted into an organic solvent to catalyze the reduction of cyanide (CN^?), carbon monoxide (CO), and carbon dioxide (CO₂) without using adenosine triphosphate (ATP), when samarium(II) iodide (SmI₂) and 2,6‐lutidinium triflate (Lut‐H) are employed as a reductant and a proton source, respectively. Driven by SmI₂, the cofactors catalytically reduce CN^? or CO to C₁–C₄ hydrocarbons, and CO₂ to CO and C₁–C₃ hydrocarbons. The C? C coupling from CO₂ indicates a unique Fischer–Tropsch‐like reaction with an atypical carbonaceous substrate, whereas the catalytic turnover of CN^?, CO, and CO₂ by isolated cofactors suggests the possibility to develop nitrogenase‐based electrocatalysts for the production of hydrocarbons from these carbon‐containing compounds.     

Quartz Rod Coated with Modified Silica Gel as a Source of CO and CO2 for Standard Gaseous Mixtures

Quartz rods coated with a thin layer of chemically modified silica gel have been used for the generation of a two-component gaseous standard mixture containing carbon monoxide and carbon dioxide. A new method based on thermal decomposition of immobilized compounds chemically bonded to the surface of silica gel has been used in the generation process. The oxalic acid moiety bonded to the glycydoxypropylsilylated surface of silica gel underwent decarbonylation and decarboxylation at 300°C, yielding carbon monoxide and carbon dioxide. On-line connection of a thermal desorber with the GC/FID enabled calibration of the detector following the process of methanization of CO and CO₂. The following amounts of CO and CO₂ were generated per unit length of the rod: 15.1 × 10⁻⁸ Mol cm⁻¹ (RSD = 5.71%) for CO and 34.2 × 10⁻⁸ Mol cm⁻¹(RSD = 5.16%) for CO₂.     

Effect of Reductive Treatment on the Magnetic Properties of HoBa2Cu3Oy and NdBa2Cu3Oy Oxide Systems

The effect of the reductive treatment of perovskite-like RBa₂Cu₃O _y (R = Ho, Nd) complex oxides in a CO atmosphere on their superconducting and magnetic properties is studied by ESR spectroscopy. ESR spectra of initial RBa₂Cu₃O _y phases exhibit only a low-field absorption signal in the zero field (T = 77 K). This signal disappears after the exposure of test samples to carbon monoxide. The analysis of ESR spectra of reduced samples points to the formation of regions with high local concentrations of isolated Cu²⁺ ions and Cu²⁺–Cu²⁺ dimers. The concentration of these paramagnetic species significantly decreases with an increase in the degree of reduction.     

Fundamental metal carbonyl equilibria: III. A quantitative study of the equilibrium between dirhodium octacarbonyl and tetrarhodium dodecacarbonyl under carbon monoxide pressure. A correction

Previously reported (J. Organomet. Chem., 246 (1983) 309) experimental data for the equilibrium constants and thermodynamic parameters of the reversible reaction 2 Rh₂(CO)₈ ? Rh₄(CO)₁₂ + 4 CO have been re-evaluated using more reliable values for the solubility of carbon monoxide in hexane at lower than room temperature and introducing also a fugacity vs. pressure correction for carbon monoxide. The new values are: ΔH0 = 58.6 ± 10 kJ mol^?1 and ΔS⁰ = 305 ± 25 J mol^?1 K^?1     

Electrocatalysts Derived from Copper Complexes Transform CO into C2+ Products Effectively in a Flow Cell

Electrochemical reactors that electrolytically convert CO₂ into higher-value chemicals and fuels often pass a concentrated hydroxide electrolyte across the cathode. This strongly alkaline medium converts the majority of CO₂ into unreactive HCO₃⁻ and CO₃²⁻ byproducts rather than into CO₂ reduction reaction (CO2RR) products. The electrolysis of CO (instead of CO₂) does not suffer from this undesirable reaction chemistry because CO does not react with OH⁻. Moreover, CO can be more readily reduced into products containing two or more carbon atoms (i. e., C₂₊ products) compared to CO₂. We demonstrate here that an electrocatalyst layer derived from copper phthalocyanine ( CuPc ) mediates this conversion effectively in a flow cell. This catalyst achieved a 25 % higher selectivity for acetate formation at 200 mA/cm² than a known state-of-art oxide-derived Cu catalyst tested in the same flow cell. A gas diffusion electrode coated with CuPc electrolyzed CO into C₂₊ products at high rates of product formation (i. e., current densities ≥200 mA/cm²), and at high faradaic efficiencies for C₂₊ production (FE_C2+; >70 % at 200 mA/cm²). While operando Raman spectroscopy did not reveal evidence of structural changes to the copper molecular complex, X-ray photoelectron spectroscopy suggests that the catalyst undergoes conversion to a metallic copper species during catalysis. Notwithstanding, the ligand environment about the metal still impacts catalysis, which we demonstrated through the study of a homologous CuPc bearing ethoxy substituents. These findings reveal new strategies for using metal complexes for the formation of carbon-neutral chemicals and fuels at industrially relevant conditions.