Mechanisms of hydrocarbon synthesis

Mechanism of Hydrocarbon Synthesis over Fischer Tropsch Catalysts P. Biloen and W. M. H. Sachtler Surface Reactions and Selectivity in Electro-catalysis... 

From their scheme of dimerization of methylene radicals, Eidus and co-workers assigned exceptional importance to ethylene in the mechanism of hydrocarbon synthesis. Because both of its carbons can add new methylene radicals, its conversion is expected to occur at a high rate,... 

Biloen P, Sachtler WMH. Mechanism of hydrocarbon synthesis over Fischer-Tropsch catalysts. Adv Catal. 1981 30 165-216. 

Mechanism of Hydrocarbon Synthesis over Fischer-Tropsch Catalysts... 

Basic research work. Emmett, Storch, Taylor, and co-workers, and other scientists carried out basic research work which directly or indirectly influenced the development work on catalysts for hydrocarbon synthesis. The studies of Emmett and Brunauer on adsorption of gases by different types of catalysts (75a) and the publications of Taylor and co-workers on activated adsorption (75b) are of particular importance. Emmett also published investigations on the reaction mechanism of hydrocarbon synthesis (Sec. III.4). 

Stage 1, if assumed to be irreversible and taking place on a nearly free surface, explains the reaction kinetics [Eq. (274)] in the high temperature range (82). Stages 2 and 3 correspond to the notions of Eidus and Zelinskii (86,87) on the mechanism of catalytic synthesis of hydrocarbons from CO and H2. Stages 5 and 6 reproduce the mechanism of reaction (273) that will be discussed in detail in Section XVII. 

Craxford, S.R. and Rideal, E.K. The mechanism of the synthesis of hydrocarbons from water gas. Journal of Chemical Society, 1939, 1604. 

This chapter is concerned with the work reported in the literature on the steam reforming df hydrocarbons which has been done since 1974 when the earlier review by Ross was written. For continuity some reference has had to be made to research covered in that review and some work before 1974 not described there is included here. Hydrocarbon steam reforming is still a process of major importance for the manufacture of hydrogen, synthesis gases, and town gas and, in the last five years, for the production of substitute natural gas. The study of reactions between hydrocarbon and steam on catalytic surfaces has continued to be an area of interest, throwing light on the mechanism of hydrocarbon decomposition and on the properties, of metal surfaces. 

The fact that fused iron catalysts of the synthetic ammonia type were successively used in many investigations of hydrocarbon synthesis for both fluidized and fixed catalyst bed operations is of interest in different respects. Due to this fact it is possible to make use of the valuable experience obtained during development work of the ammonia synthesis (73). This applies to the reduction, the tendency to oxidize, and the effect of promoters and poisons, and to a certain extent also to questions regarding the reaction mechanism. 

Experiments have recently been completed by Kummer, DeWitt, and Emmett (75), using C as a tracer in the synthesis on an iron catalyst. The results are inconclusive. If the total catalyst surface is uniformly active in the synthesis, the results show that only a small fraction of the reaction proceeds by way of the carbide. However, if only occasional active patches of the surface are participating in the synthesis, then it is possible to interpret the results as indicating that all of the reaction proceeds by way of the carbide. The carbide intermediate hypothesis for the mechanism of the synthesis on iron catalysts, however, is probably incorrect. Thus, the results of recycle operations at low temperatures on iron catalysts show that alcohols are formed earlier in the synthesis than olefinic hydrocarbons. 

Friedel-Crafts (Lewis) acids have been shown to be much more effective in the initiation of cationic polymerization when in the presence of a cocatalyst such as water, alkyl haUdes, and protic acids. Virtually all feedstocks used in the synthesis of hydrocarbon resins contain at least traces of water, which serves as a cocatalyst. The accepted mechanism for the activation of boron trifluoride in the presence of water is shown in equation 1 (10). Other Lewis acids are activated by similar mechanisms. In a more general sense, water may be replaced by any appropriate electron-donating species (eg, ether, alcohol, alkyl haUde) to generate a cationic intermediate and a Lewis acid complex counterion. 

Fe, Co or Ni is also crucial in the catalytic decomposition of hydrocarbon. In order to efficiently obtain CNT and to control its shape, it is necessary and indispensable to have enough information on chemical interaction between carbon and these metals. It is quite easy for the catalytic synthesis method to scale up the CNT production (see Chap. 12). In this sense, this method is considered to have the best possibility for mass produetion. It is important to further improve the process of catalytie synthesis and, in order to do so, clarifieation of the mechanism of CNT growth is necessary to control the synthesis. CNT can be synthesized by the chemical reaction at relatively low... 

Faraday, in 1834, was the first to encounter Kolbe-electrolysis, when he studied the electrolysis of an aqueous acetate solution [1], However, it was Kolbe, in 1849, who recognized the reaction and applied it to the synthesis of a number of hydrocarbons [2]. Thereby the name of the reaction originated. Later on Wurtz demonstrated that unsymmetrical coupling products could be prepared by coelectrolysis of two different alkanoates [3]. Difficulties in the coupling of dicarboxylic acids were overcome by Crum-Brown and Walker, when they electrolysed the half esters of the diacids instead [4]. This way a simple route to useful long chain l,n-dicarboxylic acids was developed. In some cases the Kolbe dimerization failed and alkenes, alcohols or esters became the main products. The formation of alcohols by anodic oxidation of carboxylates in water was called the Hofer-Moest reaction [5]. Further applications and limitations were afterwards foimd by Fichter [6]. Weedon extensively applied the Kolbe reaction to the synthesis of rare fatty acids and similar natural products [7]. Later on key features of the mechanism were worked out by Eberson [8] and Utley [9] from the point of view of organic chemists and by Conway [10] from the point of view of a physical chemist. In Germany [11], Russia [12], and Japan [13] Kolbe electrolysis of adipic halfesters has been scaled up to a technical process. 

Among the wide variety of organic reactions in which zeolites have been employed as catalysts, may be emphasized the transformations of aromatic hydrocarbons of importance in petrochemistry, and in the synthesis of intermediates for pharmaceutical or fragrance products.5 In particular, Friede 1-Crafts acylation and alkylation over zeolites have been widely used for the synthesis of fine chemicals.6 Insights into the mechanism of aromatic acylation over zeolites have been disclosed.7 The production of ethylbenzene from benzene and ethylene, catalyzed by HZSM-5 zeolite and developed by the Mobil-Badger Company, was the first commercialized industrial process for aromatic alkylation over zeolites.8 Other typical examples of zeolite-mediated Friedel-Crafts reactions are the regioselective formation of p-xylene by alkylation of toluene with methanol over HZSM-5,9 or the regioselective p-acylation of toluene with acetic anhydride over HBEA zeolites.10 In both transformations, the p-isomers are obtained in nearly quantitative yield. 

Hydrazide chemiluminescence has been investigated very intensively during recent years (for reviews, see 1>, p. 63, 2>, 90>). Main topics in this field are synthesis of highly chemiluminescent cyclic diacyl hydrazides derived from aromatic hydrocarbons, relations between chemiluminescence quantum yield and fluorescence efficiency of the dicarboxylates produced in the reaction, studies concerning the mechanism of luminol type chemiluminescence, and energy-transfer problems. 

The purpose of the present paper is to offer a contribute to the understanding of the mechanisms of these reactions by using an IR spectroscopic method and well-characterized "monolayer" type vanadia-titania (anatase) as the catalyst. We will focus our paper in particular on the following subjects i) the nature of the activation step of the methyl-aromatic hydrocarbon ii) the mechanism of formation of maleic anhydride as a by-product of o-xylene synthesis iii) the main routes of formation of carbon oxides upon methyl-aromatic oxidation and ammoxidation iv) the nature of the first N-containing intermediates in the ammoxidation routes. 

Water, carbon dioxide, olefin hydrocarbons, and alcohols are shown as products. It is obvious that other equations could be written showing the formation of hydrocarbons of other types—that is CH4, C2H6—and of the other oxygenates produced in this synthesis. Although Equations 8, 9, and 10 do not represent the reaction mechanism but simply express the stoichiometry of the system, they do indicate certain fundamental actions that... 

V. L. Yarovenko Theory and Practice of Continuous Cultivation of Microorganisms in Industrial Alcoholic Processes. - Y. Miura Mechanism of Liquid Hydrocarbon Uptake by Microorganisms and Growth Kinetics. -J. E. Zajic, N. Kosaric, J. D. Brosseau Microbial Production of Hydrogen. - T.Enatsu, AShin-myo In vitro Synthesis of Enzymes. Physiological Aspects of Microbial Enzyme Production. 

A similar mechanism has been proposed for photonitrosylations, with the difference that the reaction of the alkyl radical with NOC1 (Eq. 5) is not competitive (absence of chain reaction) and that the rate of reaction 6 cannot prevent dismutation (Eq. 4) and subsequent radical polymerization of unsaturated hydrocarbons (e.g., cyclohexene in the case of caprolactam synthesis). 

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