Carbon monoxide reaction kinetics

The carbon monoxide reaction is well studied and the observed kinetics are well understood. Of particular interest is the so-called CO-inhibiting regime , characterized by carbon dioxide covering and blocking the surface, so that the reaction rate is governed by CO desorption rate (see original citations in [78]). 

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. 

The extent to which each of the main reactions contributes to the removal of carbon monoxide, hydrocarbons and nitrogen oxides depends on the catalyst formulation and the catalyst operating conditions. Detailed kinetic data for these reactions are rarely found in the literature. Some fundamental data do exist for the oxidation of carbon monoxide, reaction 11, and some overall kinetic data exist for the other reactions [15-19],... 

The kinetics of the photoeatalytic reduction of NO by CO to CO2, N2O, and N2 over MoOa/Si02 catalysts at ambient temperature has been studied mass-spectroscopically using C labeled carbon monoxide. The kinetic data obtained for CO-NO mixtures of different compositions fit well the proposed redox mechanism, which suggest a paramagnetic complex (Mo ". ..NO ") as reaction intermediate. The formation of this complex is proven by EPR experiments. 

The role of siroheme in the reduction of nitrite is supported by the observation that nitrite perturbs the spectrum of the oxidized or reduced enzyme. Carbon monoxide reaction with the reduced siroheme can be followed spec-trophotometrically. The complex can be dissociated with oxygen. The kinetics of CO-complex formation and dissociation correspond with those for CO inhibition of nitrite reductase. The inhibition of nitrite reductase by p-chloromercuribenzoate, phenyl mercury acetate, and sodium mersalyl demonstrate the involvement of SH groups presumably associated with cysteine residues found in nitrite reductase. Epr studies and spectral data indicate the oxidation/reduction of iron sulfur centers and the formation of a NO-heme complex however, other intermediates have not been confirmed (Aparicio et al., 1975 Vega and Kamin, 1977 Hucklesby et al., 1979). 

Reference to Figure 3.4 shows that the reduction is not feasible at 800 K. but is feasible at 1300 K. However, we must remember that energetic feasibility does not necessarily mean a reaction will go kinetic stability must also be considered. Several metals are indeed extracted by reduction with carbon, but in some cases the reduction is brought about by carbon monoxide formed when air, or air-oxygen mixtures, are blown into the furnace. Carbon monoxide is the most effective reducing agent below about 980 K, and carbon is most effective above this temperature. 

The composition of the products of reactions involving intermediates formed by metaHation depends on whether the measured composition results from kinetic control or from thermodynamic control. Thus the addition of diborane to 2-butene initially yields tri-j iAbutylboraneTri-j -butylborane. If heated and allowed to react further, this product isomerizes about 93% to the tributylborane, the product initially obtained from 1-butene (15). Similar effects are observed during hydroformylation reactions however, interpretation is more compHcated because the relative rates of isomerization and of carbonylation of the reaction intermediate depend on temperature and on hydrogen and carbon monoxide pressures (16). 

The kinetics of this reaction, which can also be regarded as an erosion reaction, shows die effects of adsorption of the reaction product in retarding the reaction rate. The path of this reaction involves the adsorption of an oxygen atom donated by a carbon dioxide molecule on die surface of the coke to leave a carbon monoxide molecule in the gas phase. 

It was shown in laboratory studies that methanation activity increases with increasing nickel content of the catalyst but decreases with increasing catalyst particle size. Increasing the steam-to-gas ratio of the feed gas results in increased carbon monoxide shift conversion but does not affect the rate of methanation. Trace impurities in the process gas such as H2S and HCl poison the catalyst. The poisoning mechanism differs because the sulfur remains on the catalyst while the chloride does not. Hydrocarbons at low concentrations do not affect methanation activity significantly, and they reform into methane at higher levels, hydrocarbons inhibit methanation and can result in carbon deposition. A pore diffusion kinetic system was adopted which correlates the laboratory data and defines the rate of reaction. 

The first and rate-determining step involves carbon monoxide dissociation from the initial pentacarbonyl carbene complex A to yield the coordinatively unsaturated tetracarbonyl carbene complex B (Scheme 3). The decarbonyla-tion and consequently the benzannulation reaction may be induced thermally, photochemically [2], sonochemically [3], or even under microwave-assisted conditions [4]. A detailed kinetic study by Dotz et al. proved that the initial reaction step proceeds via a reversible dissociative mechanism [5]. More recently, density functional studies on the preactivation scenario by Sola et al. tried to propose alkyne addition as the first step [6],but it was shown that this... 

In contrast to the results of the reaction of tertiary and secondary alkyl cations with carbon monoxide (Figs. 1-5), which were obtained under thermodynamically controlled conditions, the results of the carbonylation with the vinyl cations were obtained under kinetically controlled conditions. This presents a difficulty in explaining the occurrence of the 1,2-CH3 shift in the reaction 16->-17, because it involves a strong increase in energy. The exclusive formation of the Z-stereoisomer 18 on carbonylation of the 1,2-dimethylvinyl cation 16 is remarkable, but does not allow an unambiguous conclusion about the detailed structure— linear 19 or bent 20—of the vinyl cation. A non-classical structure 21 can be disregarded, however, because the attack... 

This chapter is concerned initially with kinetic results and mechanistic interpretations of the CO insertion (Section III) and extrusion (Section IV) reactions. A discussion of the stereochemical data follows (Section V), and a comprehensive survey of these reactions by the triads (Section VI) rounds out the review. Carbon monoxide insertion reactions were discussed in 1967 by Basolo and Pearson (21). Since then they have been mentioned in several reviews (49, 118, 203, inter alios) but have not been treated comprehensively. 

That carbon monoxide could be oxidised in a facile reaction at cryogenic temperature (100 K) was first established in 1987 by XPS at an aluminium surface.21 The participation of reactive oxygen transients O 1 (s) was central to the mechanism proposed, whereas the chemisorbed oxide O2 state present at 295 K was unreactive. This provided a further impetus for the transient concept that was suggested for the mechanism of the oxidation of ammonia at a magnesium surface (see Chapter 2). Of particular relevance, and of crucial significance, was Ertl s observation by STM in 1992 that oxygen chemisorption at Al(lll) resulted in kinetically hot adatoms (Figures 4.1 and 4.7). 

A catalyst used for the u-regioselective hydroformylation of internal olefins has to combine a set of properties, which include high olefin isomerization activity, see reaction b in Scheme 1 outlined for 4-octene. Thus the olefin migratory insertion step into the rhodium hydride bond must be highly reversible, a feature which is undesired in the hydroformylation of 1-alkenes. Additionally, p-hydride elimination should be favoured over migratory insertion of carbon monoxide of the secondary alkyl rhodium, otherwise Ao-aldehydes are formed (reactions a, c). Then, the fast regioselective terminal hydroformylation of the 1-olefin present in a low equilibrium concentration only, will lead to enhanced formation of n-aldehyde (reaction d) as result of a dynamic kinetic control. 

This overview is organized into several major sections. The first is a description of the cluster source, reactor, and the general mechanisms used to describe the reaction kinetics that will be studied. The next two sections describe the relatively simple reactions of hydrogen, nitrogen, methane, carbon monoxide, and oxygen reactions with a variety of metal clusters, followed by the more complicated dehydrogenation reactions of hydrocarbons with platinum clusters. The last section develops a model to rationalize the observed chemical behavior and describes several predictions that can be made from the model. 

As a result of the kinetics and the equilibria mentioned above, all iodide in the system occurs as methyl iodide. The reaction in Equation (2) makes the rate of the catalytic process independent of the methanol concentration. Within the operation window of the process, the reaction rate is independent of the carbon monoxide pressure. The selectivity in methanol is in the high 90s but the selectivity in carbon monoxide may be as low as 90%. This is due to the water-gas shift reaction ... 

The kinetics of secondary hydrogenation and isomerization of 1-alkenes as represented by the reaction scheme is characterized by a negative reaction order with respect to carbon monoxide.13 15... 

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