Recombination Of Carbon Monoxide Research Articles

Recombination of carbon monoxide and oxygen atoms

AbstractThe recombination of carbon monoxide and oxygen atoms was studied in reflected shock waves in H2:O2:CO:Ar = 0.1:1:24:75 with 1300 < T5 2200 K and 2 < P5 < 4 atm. Reaction progress was monitored by observations of the carbon monoxide flame spectrum near 435 nm and carbon dioxide thermal emission near 4.2 μm. Data analysis was accomplished with the aid of computer modeling using a 27‐reaction mechanism. Computer modeling experiments also showed that these measurements were sensitive primarily to the rate of the reaction CO + O + M = CO2 + M and only slightly sensitive to the rates of other reactions. The best fit to the data was achieved with a rate constant for this reaction of 7.7 × 10−35 exp[19 kJ/RT] cm6 s for the temperature range of these experiments. Correlation of this result and previous data covering the temperature range 250 < T < 11,000 K confirms that this recombination reaction is governed by a nonadiabatic curve crossing with an activation barrier of about 20 kJ and subsequent deactivation of a singlet CO2 molecule.

The Study of Thermochemical Hydrogen Preparation. VI. A Hydrogenevolving Step through the H2S–CO Cycle

Abstract A two-step decomposition process of hydrogen sulfide was studied. The process is constituted from a hydrogen-evolution step (CO+H2S\oversetca.200°C→H2+COS) and a carbonyl sulfide-decomposition step (COS\oversetca.830°C→CO+1⁄x·Sx. Almost an equilibrium amount of hydrogen could be produced in the first reaction (ca. 40%, 200 °C, 1 atm, CO/H2S=2.2) with a cobalt sulfide or nickel sulfide catalyst. In the second reaction, an almost equilibrium amount of carbonyl sulfide (45%) could also be decomposed into carbon monoxide and elementary sulfur at 830 °C under 1 atm with a sufficient reaction rate and selectivity without using any catalysts. Carbon dioxide was formed as a by-product in the second reaction: however, its yield was only 5% of the carbon monoxide produced. From these results, it may be concluded that this two-step decomposition process of hydrogen sulfide can produce more hydrogen than that produced by the direct decomposition of hydrogen sulfide. In the second reaction, however, the recombination of carbon monoxide with elementary sulfur can not be neglected. Thus, a rapid separation of sulfur from carbon monoxide is required.

A shock tube study of the recombination of carbon monoxide and oxygen atoms

Time resolved emissions from CO2 and the radiative recombination of CO and O (flame-band emission) have been monitored in a variety of N2O/CO/Ar mixtures. These mixtures were studied behind reflected shock waves at temperatures between 2100–3200 K and total concentrations between 2.5–7.7×1018 molecule/cm3. The flame-band detector was calibrated so that absolute concentrations of atomic oxygen could be determined. These data were shown to be consistent with the following mechanism: N2O+M=N2+O+M (I), N2O+O=2NO (II), N2O+O=N2+O2 (III), with kI=4.5×10−10 exp(−226kJ/RT) cm3 molecule−1⋅ s−1 and k2=k3 =7.7×10−11 exp(−117kJ/RT). This combination was also shown to be consistent with earlier data from this laboratory. CO2 was observed to increase linearly with time in these experiments, and an apparent recombination rate constant defined as kapp≡dCO2/dt/([CO] [O] [M]) was measured and found to be a function of pressure. This behavior was attributed to the presence of very small concentrations of hydrogenous impurities. Data at higher pressures were used to estimate the rate constant for the recombination CO+O+M=CO2+M (V) since the effect of impurities was minimized here. It was found that kV= (1.6±0.3) ×10−34 cm6 molecule−2⋅ s−1 between 2100–3200 K. This value is shown to be consistent with recent studies of CO2 dissociation which report ’’normal’’ activation energies.

Recombination of carbon monoxide with hemoglobin after flash photolysis of the carboxyderivative in mixed solvents at subzero temperature

The kinetics of recombination of carbon monoxide to hemoglobin produced by total flash photolysis of its carboxyderivative are studied at low temperatures (down to −55 °C) in mixed hydroalcoholic solvents. The rates are found to be different in two solvents used, namely ethylene glycol/buffer and methanol/buffer; for the former, the rates at subzero temperatures are simply explained by cooling and are consistent with the activation energy as measured in aqueous solution, while those in methanol/buffer show evidence of a specific solvent effect. Values are reported for the rate constants and activation energies in the two solvents.

The Reaction of Carbon Monoxide with Horse Hemoglobin in Solution, in Erythrocytes, and in Crystals

Abstract Comparisons have been made of the rate of recombination of carbon monoxide with horse hemoglobin in solution, in erythrocytes, and in monoclinic crystals by means of flash photolysis. The results with solutions and erythrocytes showed close correspondence in rate and apparent activation energy. The effect of pH was also similar, hemoglobin being observed at pH 9, whereas there was a biphasic reaction at pH 7. Crystals showed rapidly reacting behavior at pH 7 and gave the same rate over a range of of ammonium sulfate concentrations from 45% of saturation to 95% of saturation, as well as in salt-free crystals. This was in contrast to hemoglobin in solution, in which increasing salt concentration raised the activity of carbon monoxide. Control experiments with whale myoglobin in solution and in crystals yielded similar rates and activation energies for the two states. It is suggested that movement of subunits in relation to one another may be restricted in hemoglobin crystals as compared with hemoglobin in solution.

Recombination of carbon monoxide and atomic oxygen at high temperatures

Recombination of carbon monoxide and atomic oxygen was studied in the expansion wave of a single-pulse shock tube at temperatures from 2800° to 3600°K, and pressures from 8.8 to 22.6 atm. This technique was found to be a simple and valuable means of studying high-temperature recombinations. Measurements of incident shock velocity and of pressure in the reflected zone, combined with relatively simple calculations of chemical equilibria, sufficed to determine quite accurately the initial conditions before expansion. Rate constants were derived from measurements of the intensity of carbon monoxide flame-band emission, which is proportional to the product of carbon monoxide and atomic oxygen concentrations. A three-body mechanism of recombination was assumed, and the results were consistent with this assumption. The lower-limit rate constants for recombination had an average value of 2×10 13 cm 6 mole −2 sec −1 and an estimated upper limit of about 1×10 14 cm 6 mole −2 sec −1 over the range of the experiments. This result is in the range of recombination constants derived from equilibrium constants and dissociation rates of carbon dioxide measured behind shock waves. The recombination rates found in the present work were lower than expected on the basis of previous direct measurements made at lower temperatures. It is suggested that surface and water catalysis may have combined to produce these discrepancies.