Hydrocarbons heterogeneous catalytic

The production of synthesis gas based on heterogeneous catalytic reactions using 02 (air) as an oxidant is referred to as catalytic POx (CPO). Although the process is potentially able to process a wide range of hydrocarbon feedstocks, including heavy hydrocarbons, most of the information in the literature relates to the CPO of methane (or NG). The CPO of methane can be presented by the following equation ... 

The decomposition of hydroperoxide on the surface of Mo and MoS2 started after some induction period (see Table 20.2). This induction period is the time for the activation of the surface toward hydroperoxide decomposition. It was evidenced in special experiments that the catalyst is not dissolved in hydrocarbon and catalytic hydroperoxide decomposition occurs only heterogeneously. 

In typical stereochemical experiments, the reactivity of two or more compounds of the same structure but of different configuration is compared either in separate or competitive experiments. The method has been reviewed several times for heterogeneous catalytic reactions, mostly with respect to reactions of hydrocarbons on metals (16-18). The results concerning eliminations on acidic catalysts have been summarized in an article dealing with the mechanism of this type of reactions (12). Clarke and Rooney (17) have broadened the notion of the stereochemical approach to heterogeneous catalysis when they included into it all work in which mechanistic conclu-... 

Formation of products containing less than four carbon atoms is not related to the catalytic activity of the metal on the decomposition of hydroperoxides. Hence, the liquid-phase oxidation of hydrocarbons involves heterogeneous catalytic reactions of isomerization and decomposition of peroxide radicals, proceeding on the reactor surface. 

A supercritical water POX technique can also be used to produce H2 for fuel cells. The solubility of supercritical water is more like high-pressure steam than water. Therefore, supercritical water can extract hydrocarbons or sulfur species of low volatility from catalyst pores in situ during a heterogeneous catalytic... 

Rate equations for heterogeneous catalytic alkylation of aromatic hydrocarbons... 

Ionization from the Heterogeneous Catalytic Oxidation of Hydrocarbons in the Vapor Phase... 

Interpretation of the mechanisms of the hydrocarbon desorption reactions mentioned above was considered (31,291) with due regard for the possible role of clay dehydration. While this water evolution process is not regarded as a heterogeneous catalytic reaction, it is at least possible that water loss occurs at an interface (293) so that estimations of preexponential factors per unit area can be made. On this assumption, Arrhenius parameters (in the units used throughout the present review) were calculated from the available observations in the literature and it was found (Fig. 9, Table V, S) that compensation trends were present in the kinetic data for the dehydration reactions of illite (+) (294), kaolinite ( ) (293,295 298), montmorillonite (x) (294) and muscovite (O) (299). If these surface reactions are at least partially reversible,... 

Some heterogeneous catalytic reactions proceed by a sequence of elementary processes certain of which occur at one set of sites while others occur at sites which are of a completely different nature. For example, some of the processes in the reforming reactions of hydrocarbons on platinum/ alumina occur at the surface of platinum, others at acidic sites on the alumina. Such catalytic reactions are said to represent bifunctional catalysis. The two types of sites are ordinarily intermixed on the same primary particles ( 1.3.2) but similar reactions may result even when the catalyst is a mixture of particles each containing but one type of site. These ideas could, of course, be extended to crea te the concept of polyfunctional catalysis. 

Superacids Immobilized on Solid Supports. The considerable success of Magic Acid and related superacids in solution chemistry and interest to extend the scope and utility of acid-catalyzed reactions, particularly hydrocarbon transformations, logically led to the attempts to adopt this chemistry to solid systems allowing heterogeneous catalytic processes. 

In summary, there is a lack of a clear concept that would allow stable anchoring of the catalytically active forms of Cr for oxidation of alcohols or hydrocarbons with t-BuOOH or O2. Immobilization of Cr by structural incorporation or ion exchange before addition of the oxidant is obviously not a guarantee for obtaining a heterogeneous catalytic process. 

For any given catalytic reaction the active surface area is normally only a small fraction of the area of the active component (active phase). The term active sites is often applied to the sites effective for a particular heterogeneous catalytic reaction. The terms active site and active centre are often used as synonyms, but active centre may also be used to describe an ensemble of sites at which a catalytic reaction takes place. There is evidence that the centres required for some catalytic reactions are composed of a collection of several metal atoms (ensemble). This appears to be the case for such reactions as, for example, hydrogenolysis, hydrogenation of CO, and certain deuterium-exchange processes with hydrocarbons. 

Another reaction of great concern is the photodechlorinatlon of chlorinated hydrocarbons. Titania has been used as a photocatalyst in the heterogeneous catalytic decomposition of chloroform and dichloromethane to form carbon dioxide and HCI by Ollls and co-workers (9) These titania catalysts are particularly useful at low levels (parts per million) of chlorinated hydrocarbon. Titania catalysts require near... 

Among the several types of homogeneously catalyzed reactions, oxidation is perhaps the most relevant and applicable to chemical industry. The well-known Wacker oxidation of ethylene to ethylene oxide is the classic example, although this is not a true catalytic process since the palladium (II) ion becomes reduced to metallic palladium unless an oxygen carrier is present. Related to this is the commercial reaction of ethylene and acetic acid to form vinyl acetate, although the mechanism of this reaction does not seem to have yet been discussed publicly. Attempts to achieve selective oxidation of olefins or hydrocarbons heterogeneously do not seem very successful. 

The oxidation of gaseous hydrocarbons over solid catalysts has been the subject of extensive industrial and academic research for many years. The mutual interest in these reactions reflects both their commercial importance and their value in studies of the fundamental features of catalytic processes. Indeed, the source of several theoretical investigations of catalytic reactions may readily be traced to developments in the modern chemical industry. Moreover, the numerous studies that have been conducted are a further reflection of the diversity of scientific interests embodied in this subject and the wide range of techniques currently available for their investigation. It is not surprising, therefore, that the heterogeneous catalytic oxidation of hydrocarbons is a subject in which a wealth of data has been accumulated and a diversity of opinions recorded. Hence, it is inevitable that in an article of this type any worthwhile inquiry into such a large field of scientific interest requires the consideration of a restricted aspect of the subject. 

Margolis, L. J., Heterogeneous Catalytic Oxidation of Hydrocarbons. Gostop-tehizdat, Moskwa, 1962. 

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