Carbon Monoxide Disproportionation Research Articles

Hydrocarbon formation upon gamma radiolysis of H 2CO mixtures in the presence of activated alumina surfaces

The formation of hydrocarbon products in the gamma radiolysis of a 3:1 hydrogen-carbon monoxide mixture in the presence of a gamma alumina catalyst has been investigated at 250 torr (33.32 kPa) pressure over a temperature range of 196–363 K where no thermally initiated reaction was detected. The yields of all products were substantially increased over those in homogeneous radiolysis with alkane yields being increased about one order of magnitude while alkene yields increased 3–4 orders of magnitude. Yields for both alkane and alkene production decreased with increasing carbon number. The predominant products were carbon dioxide, ethylene, and propylene with G-values of 59, 11, and 3.8 at room temperature. Smaller yields ( G<1) of butenes, pentenes, ethane, propane, butanes, and pentanes were found. As temperature was increased, yields of all hydrocarbon products increased, while the carbon dioxide yield diminished. The results suggest formation of higher hydrocarbon products via a stepwise mechanism with an incremental energy requirement for each additional CH 2 group. The mechanism may involve the formation of formate structures on the alumina surfaces; carbon monoxide disproportionation to CO 2 and C is not believed to be involved.

Disproportionation of carbon monoxide on supported nickel catalysts

The disproportionation of carbon monoxide was investigated mainly on a 5.5% Ni Al 2 O 3 catalyst by infrared spectroscopy and temperature-programmed desorption. The reaction was found to be of first order with respect to the surface concentration of CO below 200 °C, while at 450 °C the reaction proceeded as a second order reaction for the pressure of CO. Results obtained with predeposited carbon indicated that the disproportionation reaction requires an ensemble of several nickel atoms. In agreement with this result, the disproportionation did not take place readily on a 1.1% Ni Al 2 O 3 catalyst on which a high dispersion of the metal was indicated by both infrared spectroscopy and the chemisorption of hydrogen. In the temperature-programmed desorption (TPD) carbon monoxide desorbed in a single peak before 300 °C. Some of the carbon monoxide, however, underwent disproportionation during TPD and a carbon dioxide peak appeared at about 220 °C. Furthermore, carbon thus deposited on the surface was oxidized to carbon monoxide by oxygen supplied from the catalysts and gave a second peak of CO in TPD at temperatures higher than 300 °C. Possible sources of the oxygen were discussed.

Morphology and crystalline order in catalytic carbons

The influence of temperature and of catalyst composition on the morphology and crystalline order has been studied for a series of catalytic carbons prepared by carbon monoxide disproportionation (2CO→CO 2+C) over an iron-cobalt, an iron-nickel, and a nickel catalyst, and by methane decomposition (CH 4→2H 2+C) over a nickel catalyst. The morphology was studied by TEM in a bright field mode. The products are filamentous when prepared at low temperature and granular when prepared at high temperature. The ranges of temperature corresponding to each morphology depend both on the alloy composition and on the reacting gas. The structure of the catalytic carbons, as studied by TEM in SAD mode and by X-ray diffraction, is turbostratic (2D, i.e. biperiodic) when the carbons are prepared at low temperature and crystalline (3D, i.e. triperiodic) when prepared at high temperature. When the particle size is large, the temperature of transition is about 500°C, whatever the composition of the alloy and of the reacting gas are. However, small particles are always 2D. The carbon layers, as observed by TEM in lattice fringe mode, are short and curved for turbostratic, and large and stiff for crystalline phase. Biperiodic products are not graphitizable.

New evidence for the mechanism of the fischer-tropsch synthesis of hydrocarbons

New mechanistic evidence is advanced for Fischer-Tropsch synthesis on Ru-loaded Y-type zeolites, Ru-on-silica and Co promoted on kieselguhr. The experiments were carried out in real Fischer-Tropsch conditions, i.e., at high growth rates. Experiments were done in pulse reactors and under transient reaction conditions. 13C-labeled carbon monoxide was used and addition of water and olefins to the synthesis gas was studied. From a series of well-chosen experiments it is deduced that carbon monoxide disproportionation initiates the reaction. Surface carbon is hydrogenated to methane and the reverse water-gas shift reaction accounts for water formation. Water reacts with surface carbon and forms hydroxy-species which initiate chain propagation. The mechanism accounts for a particle size effect and explains why polar conditions stimulate chain growth.

Catalytic reduction of carbon dioxide. 1. Reduction of carbon dioxide with carbon carrying potassium carbonate

The catalytic behaviour of potassium carbonate doped onto active carbon was investigated with respect to reduction of carbon dioxide. The distribution of potassium on the carbon surface was found by an X-ray microanalyzer to be uniform. The amount of oxygen trapped on the carbon surface during reaction was nearly proportional to the surface concentration of potassium. The catalytic activity with carbon doped with less than 2% potassium carbonate was proportional to the amount of trapped oxygen, while excessive doping by potassium was found to form trapped oxygen independently of the gasification of carbon. Disproportionation of carbon monoxide into carbon dioxide and carbon was found to take place readily at 700 °C, with carbon doped with 4.0 wt % potassium carbonate.

Kinetics of reactions between magnetite and carbon monoxide between 723 and 823 K

The kinetics of some reactions between carbon monoxide and magnetite were investigated between 723 and 823 K. Gas-phase mass-transfer effects within and near the porous samples and surface-reaction kinetics were considered. The experiments were done on sintered magnetite disks whose void fraction was 15 to 20 pct. A continuously weighed rotating disk reactor provided uniform mass transfer to the sample faces. The reacted disks were analyzed by Mossbauer spectroscopy and other methods. The only product species found were cementite and carbon, which suggested the existence of two reactions: the formation of cementite and carbon dioxide directly from magnetite and carbon monoxide, and the disproportionation of carbon monoxide to carbon dioxide and free carbon. These reactions were modeled mathematically. The surface kinetic data for both reactions were found to be compatible with rate expressions which were directly proportional to the square of the partial pressure of carbon monoxide and approximately inversely proportional to the partial pressure of product carbon dioxide.

Carbon from carbon monoxide disproportionation on nickel and iron catalysts: Morphological studies and possible growth mechanisms

Carbon was prepared by disproportionation of CO; Ni(CO) 4 or Fe(CO) 5 was fed to the CO stream before it entered the decomposition furnace. Electron microscopy reveals differences in the carbons obtained: adding Fe(CO) 5 resulted in the usual fibrilar growth whilst Ni(CO) 4 gave rise to spherical shells and sausage-like forms which are hollow inside. X-ray powder diffraction shows that the carbon obtained using Ni(CO) 4 is not as well organised as the carbon obtained using Fe(CO) 5. Possible formation mechanisms are discussed; very likely, the carbon shells obtained using Ni(CO) 4 are precipitated from solution in nickel whereas carbon obtained in the presence of iron is catalytically recrystallised by an iron carbide. A mechanism for the formation of helical fibres is suggested.

Hydrogen chemisorption on platinum catalysts

Hydrogen chemisorption on Pt and Pd, supported on active carbon and alumina, was determined by a rapid desorption technique. Desorption was effected by increasing the sample temperature from 21 to 370 °C in less than 1 min. The desorbed hydrogen, swept into a nitrogen carrier gas, was measured from the peak recorded by a chromatographic-type detector. Repetitive determinations on the same sample were consistent within ± 3%. The chemisorption data indicated that the dispersion of Pt on active carbon was 47, 32, and 23% for 0.5, 1.0, and 10% PtC, respectively. Evidence of carbon monoxide disproportionation on Pt at 370 °C and of hydrogen spillover from Pt to active carbon support at 370 °C was found.

Amphiboles. Part V. The catalysis of the disproportionation of carbon monoxide by crocidolite

Crocidolite is shown to effect the disproportionation of carbon monoxide after an induction period of several hours during which only reduction of iron(III) to iron(II) and some chemisorption of carbon monoxide occur. Disproportionation does not take place in contact with crocidolite which has been previously oxidised or is in the anhydride form, but proceeds without any induction period if the amphibole has been prereduced with hydrogen. It is postulated that reaction occurs only on the surface of the crocidolite, and that the disproportionation is catalysed by atoms of iron(0). It is suggested further that the presence of hydroxyl ions is necessary for the formation of iron(0) in the reaction between carbon monoxide and fresh crocidolite, and that their absence accounts for the lack of catalytic activity of the oxidised and anhydride forms.

Reaction of nickel with carbon monoxide at elevated temperatures

The reaction of sheet nickel with carbon monoxide has been examined over the temperature range 300–650 °C with a tracer apparatus employing C 14-labeled carbon monoxide. Evidence has been produced that the main reaction at all temperatures was the catalytic disproportionation of carbon monoxide upon the nickel surface, i.e., 2 CO → C + CO 2 with direct reaction between nickel and carbon monoxide playing a minor, even negligible, role. The disproportionation reaction takes place readily upon abraded nickel surfaces but only with great difficulty upon electropolished surfaces. Possible explanations are suggested.