Carbon monoxide kinetic study

To study this discrimination, generally expressed as an M value, the ratio of the O2 and CO equilibrium constant values, researchers have used sterically hindered porphyrins (capped, pocket and hybrid porphyrins) with a view to providing an environment which would permit normal binding of dioxygen whilst hindering the binding of carbon monoxide. Kinetically, the major effect is a decrease in CO association rates, consistent with steric blocking in productlike transition states. 

The platinum catalyzed CO oxidation of carbon monoxide was studied using an advanced transient reactor system, referred to as Multitrack. The experiments indicate, that the reaction is taking place according to the Langmuir-Hinshelwood reaction model. The desorption of CO from the catalyst surface was shown to be a kinetically relevant step in the reaction. From experiments performed using it was shown that isotopic mixing occurs on the catalyst surface due to the decomposition of CO present on the catalyst surface. 

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... 

An overall kinetic study on the Koch synthesis of succinic acid from acrylic acid and carbon monoxide in SO3—HaS04 has recently been reported (Sngita et. al., 1970). 

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]). 

Chang SC, Hamelin A, Weaver MJ. 1991. Dependence of the electrooxidation rates of carbon monoxide at gold on the surface crystallographic orientation A combined kinetic-surface infrared spectroscopy study. J Phys Chem 95 5560-5567. 

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. 

All preparations were structurally characterized by means of XRD (Siemens 5005). TEM imaging was performed with a Philips CM200 instrument. 27A1 and 29Si MAS NMR (Broker 500 MFlz and 360 MFlz respectively) was used to study the microporous phase and the kinetic of its formation. The relaxation delays were 0.2s and 200s respectively. Acidity was determined by the adsorption of carbon monoxide after activating the samples in vacuum (10 6 mbar) at 450°C for 1 h. The spectra were recorded on a Equinox 55 Broker spectrometer with a resolution of 2 cm 1 and normalized to 10 mg of sample. 

Sarup, B., and Wojciechowski, B.W. 1989. Studies of the Fischer-Tropsch synthesis on a cobalt catalyst. II. Kinetics of carbon monoxide conversion to methane and to higher hydrocarbons. Can. J. Chem. Eng. 67 62-74. 

The only dependencies noted in the kinetic studies were first-order dependencies on iodide promoter and rhodium concentrations. Thus there was no observed effect of varying methanol concentration, and the partial pressure of carbon monoxide had no effect on the reaction rate. Similarly, the concentration of the products, methyl acetate and acetic acid, has no effect on the reaction rate. Thus we have the unusual situation of a reaction, CH3OH + CO — CH3COzH, in which the concentrations of the reactants and product have no kinetic influence. 

The purpose of this article is to review the results of transient low pressure studies of carbon monoxide oxidation over transition metal substrates. Particular emphasis is given to the use of in-situ electron spectroscopy, flash desorption, modulated beam and titration techniques. The strengths and weaknesses of these will be assessed with regard to kinetic insight and quantification. An attempt will be made to identify questions that are ripe for investigation. Although not limited to it, the presentation emphasizes our own work. A very recent review of the carbon monoxide oxidation reaction C l) will be useful to readers who are interested in a more comprehensive view. 

Just as in gas phase kinetics, reactive molecular beam-surface scattering is providing important molecular level insight into reaction dynamics. There is no surface reaction for which such studies have proven more illuminating than the carbon monoxide oxidation reaction. For example Len, Wharton and co-workers (23) found that the product CO exits a 700K Pt surface with speeds characteristic of temperatures near 3000K. This indicates that the CO formed by the reactive encounter of adsorbed species is hurled off the surface along a quite repulsive potential. 

The Dotz reaction mechanism has received further support from kinetic and theoretical studies. An early kinetic investigation [37] and the observation that the reaction of the metal carbene with the alkyne is supressed in the presence of external carbon monoxide [38] indicated that the rate-determining step is a reversible decarbonylation of the original carbene complex. Additional evidence for the Dotz mechanistic hyphotesis has been provided by extended Hiickel molecular orbital [23, 24] and quantum chemical calculations [25],... 

Cobalt, as its CpCo(CO)2 complex, has proven to be especially suited to catalyze [2 + 2 + 2] cycloadditions of two alkyne units with an alkyne or alkene. These cobalt-mediated [2 + 2 + 2] cycloaddition reactions have been studied in great detail by Vollhardt337. The generally accepted mechanism for these cobalt mediated cycloadditions, and similar transition metal mediated cycloadditions in general, has been depicted in equation 166. Consecutive co-ordination of two triple bonds to CpCo(CO)2 with concomitant extrusion of two molecules of carbon monoxide leads to intermediates 578 and 579 via monoalkyne complex 577. These react with another multiple bond to form intermediate 580. The conversion of 578 to 580 is said to be kinetically favored over that of 579 to 580. Because intermediates like 580 have never been isolated, it is still unclear whether the next step is a Diels-Alder reaction to form the final product or an insertion to form 581. The exact circumstances might determine which pathway is followed. 

Prior to 1970 our understanding of the bonding of diatomic molecules to surfaces, and in many cases the type of adsorption (i.e., molecular or dissociative) was almost entirely dependent on indirect experimental evidence. By this we mean that deductions were made on the basis of data obtained from monitoring the gas phase whether in the context of kinetic studies based on gas uptake or flash desorption, mass spectrometry, or isotopic exchange. The exception was the important information that had accrued from infrared studies of mainly adsorbed carbon monoxide, a molecule that lent itself very well to this approach owing to its comparatively large extinction coefficient. 

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