Carbon Monoxide Selectivity Research Articles

Selectivity and composition dependence of response of gas-sensitive resistors. Part 1.—Propane–carbon monoxide selectivity of Ba6FexNb10 –xO30(1 ⩽x⩽ 2)

A series of tetragonal tungsten bronze structure compounds of formula Ba6FexNb10 –xO30(1 < x < 2) have been made and characterised by X-ray powder diffraction and electron microprobe analysis. The compounds were ostensibly single-phase materials, but since their electrical conductivity did not vary with composition, their structure was interpreted as being Ba6FeNb9O30 with intergrowths of, possibly, BaFe2O4. The gas-sensing behaviour to propane and carbon monoxide was investigated. The compounds were n-type semiconductors, exhibiting a resistance decrease in the presence of ppm levels of the gases in air. Pellets were found to show some selectivity to propane over carbon monoxide which increased with temperature in the range 400–485 °C. The selectivity was shown to be dependent on the porosity of the pellets. There was no systematic variation of either sensitivity or selectivity with stoichiometry, x. Temperature-programmed mass spectrometric experiments showed that the onset of carbon monoxide oxidation occurred at 310 °C over these compounds, while propane combustion started at 420 °C. The propane–carbon monoxide selectivity was interpreted as being due to differences in the combustion kinetics of the two gases which resulted in different gas concentration gradients within the pellet. This was confirmed by using a novel electrode geometry, which enabled the resistance to be measured simultaneously at both the centre and the edge of a pellet.

Fischer-Tropsch Reaction Studies with Supported Ruthenium Catalysts .III. The Production of Alkenes and High Molecular Weight Hydrocarbons in a Fixed Bed Reactor

An investigation was undertaken to examine the production of low molecular weight alkenes (C=2 to C=4) and high molecular weight hydrocarbons (C+5) from synthesis gas in a fixed bed reactor with supported ruthenium catalyst. The catalyst used consisted of 0.5% ruthenium on gamma-alumina with a 43% metal dispersion. An experimental reactor consisting of a single 12.5-mm-diameter stainless-steel tube with catalyst packings up to 1 m long, surrounded by an aluminium block with heating elements and an outer insulating ceramic block was used. The effect of temperature, synthesis gas composition (CO/H2), weight hourly space velocity (WHSV), and bed length on carbon monoxide conversion and selectivity was examined and results are reported. The presence of secondary reactions consisting of hydrogenation and chain growth involving alkenes along the reactor bed was observed. These reactions favour the formation of alkanes and high molecular weight hydrocarbons. The alkene to alkane ratio in the product can be increased by restricting the hydrogenation reaction with the use of a synthesis gas mixture with a high carbon monoxide to hydrogen ratio.

Partial oxidation of methane to carbon monoxide and hydrogen over a Ni/Al 2O 3 catalyst

Partial oxidation of methane occurs in the temperature range 450–900°C by reaction of an oxygen-deficient CH 4/O 2 mixture over a 25 wt% Ni/Al 2O 3 catalyst. Carbon monoxide selectivities approaching 95% and virtually complete conversion of the methane feed can be achieved at temperatures >700°C. The oxidation state and phase composition of the catalyst were characterized using X-ray photoelectron spectroscopy and X-ray powder diffractometry. This study revealed that, under operating conditions, the previously calcined catalyst bed consists of three different regions. The first of these, contacting the initial CH 4/O 2/He feed mixture, is NiAl 2O 4, which has only moderate activity for complete oxidation of methane to CO 2 and H 2O. The second region is NiO + Al 2O 3, over which complete oxidation of methane to CO 2 occurs, resulting in an exotherm in this section of the bed. As a result of complete consumption of O 2 in the second region, the third portion of the catalyst bed consists of a reduced Ni/Al 2O 3 phase. Formation of the CO and H 2 products, corresponding to thermodynamic equilibrium at the catalyst bed temperature, occurs in this final region, via reforming reactions of CH 4 with the CO 2 and H 2O produced during the complete oxidation reaction over the NiO/Al 2O 3 phase.

Synergy between Stable Carbonates and Yttria in Selective Catalytic Oxidation of Methane

Abstract The use of yttria as an oxidative coupling of methane catalyst leads to relatively high carbon monoxide selectivity. This behavior, identical to that found with thoria, is believed to be due to the absence of carbonate formation and the stability of surface superoxide on these two oxides. The addition of high temperature stable alkaline earth carbonates decreases CO synthesis activity while increasing overall catalytic activity.

Feasibility of Using Oscillatory Catalytic Oxidation Phenomenon for Selective Carbon Monoxide Sensing

Tin dioxide based sensors with different additives were constructed and tested in air environment containing carbon monoxide. Conductance oscillations were observed in samples containing palladium but not in those without. Oscillations occurred at temperatures ranging from 150℃ to 320℃. Within this temperature region the range of CO concentrations at which oscillations appeared became higher as the test temperature increased. The lowest CO concentration at which oscillations were observed was 200 ppm and the highest 10000 ppm.By comparing sensor responses obtained in synthetic and ambient air it was concluded that water vapour has a major influence on oscillations and increases the frequency. The ranges of CO concentrations in which oscillations occurred at different temperatures, however, remained roughly the same in both environments. It was also noticed that processing conditions had an influence on the oscillatory response characteristics of the sensors.

Selective carbon monoxide adsorbent composed of polystyrene resin having amino groups and copper(I) chloride

AbstractA carbon monoxide adsorbent composed of 10 g of a polystyrene resin having amino groups and 70 mmol of copper(I) chloride was prepared by refluxing the resin and copper(I) chloride in acetonitrile, followed by evaporation of the liquid phase at 5 mmHg, 80°C. The adsorbent rapidly adsorbs 15.9 mmol of carbon monoxide under 1 atm at 20°C. 11.4 mmol of adsorbed carbon monoxide are desorbed when the adsorbent is subjected to a reduced pressure (5 mmHg) at 80°C for 10 min. In the second and the later adsorptions, the amount of adsorbed carbon monoxide is virtually constant at 11.4 mmol. The amount of carbon dioxide adsorbed by the adsorbent under 1 atm at 20°C is 2.8 mmol, and the value for methane is 0.0 mmol. The prepared adsorbent is applicable to selective separation of carbon monoxide from gas mixtures containing both carbon dioxide and methane.

The catalytic activity and selectivity of supported vanadia catalysts doped with alkali metal sulphates.: II. The role of sulphur in determining activity and selectivity of carbon monoxide and benzene oxidation

The importance of sulphur oxides in determining the activity and selectivity of vanadia-alkali metal sulphate catalysts has been studied using the oxidation of carbon monoxide and of benzene as test examples. The oxidation of carbon monoxide is well described by the Redox model for vanadia catalysts and rate constants were calculated for the reduction and reoxidation of the catalyst. Both rate constants passed through a minimum at a molar ratio of SO 3:K 2SO 4 in the catalyst of 1.0-1.2, and the activity pattern observed was explained in terms of the sulphates/ pyrosulphates probably present in the catalyst. The oxidation of benzene involves the interaction of adsorbed species, the reaction being catalysed by complexes of the type xV 2O 5·yK 2SO 4·zSO 3. The oxidation was well described by a triangular reaction network in which the rate constants for oxidation of benzene increased with the sulphur content of the catalyst. Optimal conditions for high selectivity oxidations are established.

Pyrolysis of nuclear reactor circulator oil in carbon dioxide

The ingress of circulator oil into the carbon dioxide coolant of a nuclear reactor can cause problems such as the deposition of carbon on the fuel elements. This paper describes the first stage of degradation when oil is pyrolysed, in carbon dioxide at temperatures between 600 and 900°C, and in helium at 900°C, for 20s. The degradation products were determined using gas chromatography with either a selective carbon monoxide monitor or a flame ionization detector. The chromatograph was combined with a mass spectrometer for the identification of the degradation produces. Hydrogen, carbon monoxide and a wide range of hydrocarbons are the initial degradation products. The amounts of individual reaction product, and the total amount formed ( P) increased with pyrolysis temperature, T, according and the total amount = 1/ T. The sensitivity to temperature of product formation varied from one product to another. Formation of carbon monoxide was least sensitive to temperature. It is clear that a chemical reaction takes place between the oil and carbon dioxide since the total amounl of product produced is much greater in carbon dioxide than in helium and the relative amounts of product produced in carbon dioxide differ considerably from those produced by pyrolysis in helium: for example, no carbon monoxide is detected when the oil is pyrolysed in helium.