Gas-phase Carbon Monoxide Research Articles

Oscillations in the non-steady state oxidation of carbon monoxide over supported monometallic palladium, cerium and cobalt and bimetallic palladium—cerium and palladium—cobalt catalysts

Adsorption of carbon monoxide and the reaction of preadsorbed carbon monoxide species and gas-phase carbon monoxide with oxygen over alumina-supported monometallic palladium, cerium and cobalt and bimetallic palladium-cerium and palladium-cobalt catalysts have been investigated. Temperature-programmed desorption and differential scanning calorimetry were used for studying the reaction. Thermal effects of both the adsorption and reaction were measured. Self-sustained oscillations of the reaction heat and product composition during the reaction between preadsorbed carbon monoxide and gas phase carbon monoxide with oxygen were observed. A plausible mechanism for the reaction is presented.

The lability of carbon monoxide adsorbed on rhodium

Carbon monoxide which is retained by a rhodium surface after heating to 573 K exchanges with gas phase carbon monoxide at 293 K. The retained species is postulated as *−C=O−*.

Some observations on the kinetics of the hydrogenation of carbon monoxide

For the hydrogenation of CO a positive order of hydrogen and a slightly negative or a zero order in carbon monoxide are generally reported. The negative (or zero) order in carbon monoxide is often explained by assuming a strong adsorption of carbon monoxide on the same sites as used by the hydrogen. It is then assumed that the surface is ''almost totally'' covered by carbon monoxide. From experiments in which the surface products on an unsupported cobalt catalyst after the reaction were stripped off by a hydrogen treatment it was concluded that more than 95% of the surface (as determined from the adsorption of carbon monoxide at room temperature) was covered by carbon-containing species. This paper illustrates that ''zero order in carbon monoxide'' can be obtained with much lower coverage of carbon-containing species in equilibrium with gas-phase carbon monoxide than indicated above. Equations for reaction rates are presented, and data is calculated on the fraction of the catalyst surface covered by active carbon-containing species when the reaction is zero order in CO. The results suggest that only a small fraction of the catalyst surface is actively engaged in the hydrogenation of CO. This further suggests that the low turnover frequenciesmore » found for the Fischer-Tropsch synthesis could be caused by a small number of sites which are active in the rate-determining step. (MWF)« less

Infrared evidence for the low-temperature dissociation of CO over silica-supported RuPt bimetallic clusters

The adsorption of carbon monoxide at 25/sup 0/C was studied on previously characterized 10%Ru/Pt catalyst because ruthenium is known to adsorb carbon monoxide dissociatively and catalyze methanation, whereas platinum has low methanation and higher alcohol formation activity. IR spectra showed that small doses of carbon monoxide adsorbed associatively and then decomposed. The presence of oxygen was verified by NO adsorption and the presence of carbon by electron microprobe analysis. The dissociative adsorption proceeded to monolayer coverage and was not observed if excess gas-phase carbon monoxide was added at once. The possible precursor species for carbon monoxide dissociation is discussed.

Steady-state oxidation of carbon monoxide over supported noble metals with particular reference to platinum

Activation energies, kinetic orders, and relative activities have been determined for the oxidation of CO by O 2 over five supported noble metals. With ruthenium drifts in reaction rate occurred for many hours following pressure and temperature changes but the initial responses were qualitatively similar to the simple behavior found for iridium, rhodium, and palladium (above 390 K), namely, kinetic orders near −1 and +1 in CO and O 2, respectively, and an activation energy near 100 kJ mol −1. The platinum-catalyzed reaction had a much lower activation energy (56 kJ mol −1), and the kinetic order was only slightly negative in CO with a possible tendency for these findings to change toward those found for the other metals at temperatures above 480 K. These results were compared with the predictions of a model which used parameters derived from measurements made under uhv conditions and/or with only one reactant present in the gas phase. The two reactions indicated were those oxygen molecularly adsorbed on a near complete carbon monoxide layer and between adsorbed oxygen atoms and gas-phase carbon monoxide molecules. The kinetic results which were common to each metal conformed to that expected for this latter reaction with the rate limited by CO desorption. Under these conditions the order of metal activity should be opposite to the order of heats of adsorption of carbon monoxide, and from the measurements available such a relationship did seem to hold.

The infrared spectrum of adsorbed carbon monoxide on a platinum surface in the presence of high pressure gas-phase carbon monoxide

A wedge-filter spectrometer was used in a new experimental technique which permits measurement of < 1% absorbance due to the adsorbed species against a background signal which changes by factors of 2 or 3 over the scanned spectral range, even if up to 0.25 atm gas-phase molecules of the adsorbate are present. The method is illustrated for the adsorption of carbon monoxide on unpurified polycrystalline platinum foil with approx. 100 mm Hg of carbon dioxide present in the cell. A shift of the carbon monoxide absorption maximum with changing cell pressure is discussed. Spectra.

A transient kinetics study of the reaction of CO with chemisorbed oxygen on platinum

Transient pressure-jump experiments are reported in which the reaction between gas phase carbon monoxide and chemisorbed oxygen on polycrystalline platinum is followed using both CO2 decay and CO titration methods. The experiments are carried out at 540 °K and low pressures below 5×10−7 torr. From the data we conclude that the reaction between chemisorbed oxygen atoms and gas phase carbon monoxide is first order in CO pressure and, at high oxygen atom coverages, zero order in the adsorbed oxygen atom concentration. These results imply that CO impinging on the platinum surface visits several sites during the course of a single encounter.

Poisoning of a supported molybdenum olefin disproportionation catalyst

Nitric oxide and carbon monoxide have been used to poison a propene disproportionation catalyst prepared from molybdenum hexacarbonyl on silica. Nitric oxide is strongly adsorbed, and an effective poison, but infra-red spectra indicate that adsorption occurs on more than one type of site, so that estimates of the active sites obtained are upper limits only. The nitric oxide poisoning experiments have shown that molybdenum is well dispersed on the silica support. Carbon monoxide is not strongly adsorbed; the slight poisoning effect observed can be accounted for in terms of competition between gas phase carbon monoxide and propene for the active sites.

Catalysis by tungsten of oxygen transfer from nitrous oxide to carbon monoxide

A tungsten filament which had been partially oxygenated by reaction with nitrous oxide exchanged oxygen with gas-phase carbon monoxide when the filament temperature was raised to 840 K. However, the fully oxygenated filament did not exchange most of the adsorbed oxygen with carbon monoxide until its temperature reached 1370 K. The transfer of oxygen from nitrous oxide to carbon monoxide when an equimolar mixture of the gases streamed over the filament was not measurable until the filament was hot enough to decompose some of the nitrous oxide continuously. Above this temperature the rate of transfer increased smoothly with rise in filament temperature.