Carbon monoxide disproportionation

The Cothane Process. - This is a process for the removal of traces of CO from waste-gas streams and its conversion to pipe-line quality SNG.37 The process depends on the fact that carbon monoxide disproportionates at 200 °C on Ni surfaces according to the Boudouard reaction ... 

The reason why the minimum steam ratio goes down with temperature is not known with certainty. One possibility is that the competing reactions of carbon production and consumption have such kinetics that the rate of coke consumption increases faster with temperature than the rate of coke generation, which suggests that the carbon-steam reaction has a higher activation energy than the methane cracking and carbon monoxide disproportionation reaction. 

The initial gaseous product of decomposition, carbon monoxide, disproportionated. The extent was greatest for cerium(III) oxalate (72%) and least for the gadolinium salt (58%), following almost the reverse order to that given above. 

Erbium and lutetium oxalates [81] decomposed after long induction periods required for complete dehydration. The carbonates which then formed were unstable and dissociated to yield oxides. The extents of carbon monoxide disproportionation during breakdown of these reactants were smaller (17% for Er and 6% for Lu). 

The behaviour of yttrium oxalate (573 K) was [82] generally similar to Aat of the lanthanide oxalates. No carbonate could be detected, suggesting that the carbonate is less stable than the oxalate. Carbon monoxide disproportionation proceeded to about 60%, accompanied by carbon deposition. 

The decomposition products identified following reaction are not necessarily the primary compounds which result directly from the rate limiting step. Particularly reactive entities may rapidly rearrange before leaving the reaction interface and secondary processes may occur on the surfaces of the residual material which often possesses catalytic properties. The volatile products identified [144] from the decomposition of nickel formate were changed when these were rapidly removed from the site of reaction. The primary products of decomposition of thorium formate were identified [17] as formaldehyde and carbon dioxide, but secondary processes occurring on the residual thoria yielded several additional compounds. The oxide product similarly catalysed interactions between the primary products of decomposition of zinc acetate [145]. During the decomposition of rare earth oxalates, carbon monoxide disproportionates extensively to carbon dioxide and carbon [81,82]. 

Reactions of carboxylates containing the more electropositive cations yield product carbonates, or sometimes the basic carbonates. Some of these salts, e.g., those of the alkali metals, melt before decomposition. The oxide products from decomposition of the lanthanide compounds may contain carbon deposited as a result of carbon monoxide disproportionation. Kinetic measurements must include due consideration of the possible retention of carbon dioxide by the product (as COj ) and the secondary reactions involved in carbon deposition. 

Boehm, H.P. "Carbon from Carbon Monoxide Disproportionation on Nickel and Iron Catalysts Morphological Studies and Possible Growth Mechanisms" Carbon 1973, 11, 583. 

Figure 8.21 Schematic of ribbon and braided carbon filament morphologies. Source Reprinted with permission from Boehm HP, Carbon from carbon monoxide disproportionation on nickei and iron catatysts Morphoiogicai studies and possible growth mechanisms, Carbon, 11, 583-590, 1973. Copyright...

Decoking with Hydrogen. Hydrogen was found to be effective, but relatively slow in removing coke formed by carbon monoxide disproportionation. Hydrogen reacted with coke as follows ... 

Thermal cracking tends to deposit carbon on the catalyst surface which can be removed by steaming. Carbon deposition by this mechanism tends to occur near the entrance of the catalyst tubes before sufficient hydrogen has been produced by the reforming reactions to suppress the right hand side of the reaction. Promoters, such as potash, are used to help suppress cracking in natural gas feedstocks containing heavier hydrocarbons. Carbon may also be formed by both the disproportionation and the reduction of carbon monoxide... 

Chemica.1 Properties. Reviews of carbonyl sulfide chemistry are available (18,23,24). Carbonyl sulfide is a stable compound and can be stored under pressure ia steel cylinders as compressed gas ia equiUbrium with Hquid. At ca 600°C carbonyl sulfide disproportionates to carbon dioxide and carbon disulfide at ca 900°C it dissociates to carbon monoxide and sulfur. It bums with a blue flame to carbon dioxide and sulfur dioxide. Carbonyl sulfide reacts... 

Disproportionation. Carbon monoxide readily disproportionates into elemental carbon and carbon dioxide [124-38-9] on a catalyst surface... 

The hydroxamic acid function in most alicyclic and aromatic compounds is stable to hot dilute acid or alkali, and derivatives cannot undergo normal base-catalyzed Lessen rearrangement. Di Maio and Tardella," however, have shown that some alicyclic hydroxamic acids when treated with polyphosphoric acid (PPA) at 176°-195° undergo loss of CO, CO.2, or H2O, in a series of reactions which must involve earlj fission of the N—0 bond, presumably in a phosphoryl-ated intermediate. Thus, l-hydroxy-2- piperidone(108) gave carbon monoxide, 1-pyrroline (119), and the lactams (120 and 121). The saturated lactam is believed to be derived from disproportionation of the unsaturated lactam. 

The gained hydrogen from the water shift reaction reduces the hydrogen demand for FTS. Water gas shift proceeds at about the same rate as the FT reaction. Studies of the overall water shift reaction in FT synthesis have been reviewed by Rofer Deporter. Another side reaction also occurring in FTS reactors is the disproportionation of carbon monoxide to carbon dioxide and carbon ... 

Carbon monoxide adsorbed on sufficiently small palladium particles disproportionates to surface carbon and carbon dioxide. This does not occur on large particles. The CO-O2 reaction is shown to be structure-insensitive provided the metal surface available for the reaction is estimated correctly. 

Five- or six-membered saturated cyclic ketones can also react by another pathway that does not involve decarbonylation. In these reactions, the biradical initially formed by a-cleavage undergoes internal disproportionation without loss of carbon monoxide, resulting in the formation of either an unsaturated aldehyde or a ketene. Methanol is usually added to convert the reactive ketene to a stable carboxylic-acid derivative (Scheme 9.2). 

High-pressure in-situ NMR spectroscopy have been reported about reactions of carbon monoxide with cobalt complexes of the type, [Co(CO)3L]2. For L=P(n-C4H9)3, high pressures of carbon monoxide cause CO addition and disproportionation of the catalyst to produce a catalytically inactive cobalt(I) salt with the composition [Co(CO)3L2]+[Co(CO)4] . Salt formation is favoured by polar solvents [13],... 

Whenever carbon monoxide is present in a reacting system, it is possible for it to disproportionate into carbon dioxide according to the equilibrium... 

H. J. Dai, A. G. Rinzler, P. Nikolaev, A. Thess, D. T. Colbert, and R. E. Smalley, Single-wall nanotubes produced by metal-catalyzed disproportionation of carbon monoxide, Chem. Phys. Lett. 260, 471 75 (1996). 

The difficulty in detecting surface hydride formation is that hydrogen is nearly always contained in the bulk structure of the carbons. Hydrogen is not easily determined with sufficient accuracy if only small concentrations are present. Precise analytic methods should be used in the measurement of the hydrogen uptake of carbons that were prepared with rigorous exclusion of hydrogen-containing contaminants. Carbon formed by the disproportionation of carbon monoxide... 

Considering methods of CO2 generation, we partly broached a subject of its chemical reactivity. However, some important data should be added. Disproportionation of C02 leads to carbon monoxide and a carbonate, whereas dimerization results in the formation of oxalate (see the left and right directions of the following dual equation) 02C—C02 <— 2CO2 CO + CO... 

Nickel tetracarbonyl may be prepared in the laboratory by the Hieber process, a disproportion reaction of several nickel compounds of organic thio acids, such as nickel(II) phenyldithiocarbamate, (CeHs— NH—C(=S)—S)2Ni, with carbon monoxide under controlled conditions. In such disproportionation reactions, the divalent nickel ion converts to a tetravalent nickel complex (Hieber. H. 1952. Z.anorg.Chem., 269, pp. 28). The overall reaction is ... 

Not all reactions leading to carbonylate anions require strong reducing agents. Some involve reduction of the meta by carbon monoxide already present in the metal carbonyl or disproportionation of the complex In fact, the first synthesis of u metal carbonylate involved the former procedure ... 

The reactions of nitric oxide involve either oxidation or reduction (or both simultaneously in disproportionation and decomposition). Except for oxidation, these reactions of nitric oxide require catalysts for them to proceed at significant rates. An important stimulus to studying these catalyzed reactions lies in the environmental hazards posed by oxides of nitrogen, of which NO is the parent member, as discussed at the beginning of this section. Particular attention in the area of metal complex catalyzed reactions has focused in the last five years on the reduction of nitric oxide by carbon monoxide, (113). 

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