Catalysis hydrocarbon oxidation

Bifunctionality means that sites with different functions are present on the surface of a catalyst. In this general sense, two types of bifunctionality in hydrocarbon oxidation catalysis can be discerned. 

The scope of oxidation chemistry is enormous and embraces a wide range of reactions and processes. This article provides a brief introduction to the homogeneous free-radical oxidations of paraffinic and alkylaromatic hydrocarbons. Heterogeneous catalysis, biochemical and hiomimetic oxidations, oxidations of unsaturates, anodic oxidations, etc, even if used to illustrate specific points, are arbitrarily outside the purview of this article. There are, even so, many unifying features among these areas. 

Catalysis by Nitroxyl Radicals in Hydrocarbon Oxidation References... 

Catalysis by Transition Metal Ions and Complexes in Hydrocarbon Oxidation by Dioxygen... 

Catalysis by nitroxyl radicals in hydrocarbon oxidation was discovered and studied recently [82-89], The introduction of /V-hydroxyphthalimide into oxidized alkylaromatic hydrocarbon was found to accelerate the oxidation. The formation of the stable phthalimide-/V-oxyl (PINO) radical was evidenced by the EPR method [90]. The following kinetic scheme was put forward to explain the accelerating effect of PINO on the chain oxidation of hydrocarbons [82-84]. 

CATALYSIS BY TRANSITION METAL IONS AND COMPLEXES IN HYDROCARBON OXIDATION BY DIOXYGEN... 

Frei, H. (1997). Highly selective photochemical and dark oxidation of hydrocarbons by 02 in zeolites. In Studies in Surface Science and Catalysis. 3rd World Congress on Oxidation Catalysis, Grasselli, R.K., Oyama, S.T., Gaffney, A.M. and Lyons, J.E. (eds), Vol. 110, pp. 1041-1050. Elsevier Science, New York... 

An interesting variant of selective oxidation catalysis is the catal)hic reduction of nitrogen oxides by ammonia or hydrocarbons. In this case the reducing molecule should specifically react with NO or NO2, that are present in very low concentrations, rather than become oxidized to CO2 + H2O by reacting with O2 that is present in much higher concentration. The distinction between oxo-ions and oxide particle is most convenient if these entities are present on a zeolite support. Techniques have been developed to study the interconversion by IR spectroscopy ... 

The third and last part of the book (Chapters 12-16) deals with zeolite catalysis. Chapter 12 gives an overview of the various reactions which have been catalyzed by zeolites, serving to set the reader up for in-depth discussions on individual topics in Chapters 13-16. The main focus is on reactions of hydrocarbons catalyzed by zeolites, with some sections on oxidation catalysis. The literature review is drawn from both the patent and open literature and is presented primarily in table format. Brief notes about commonly used zeolites are provided prior to each table for each reaction type. Zeolite catalysis mechanisms are postulated in Chapter 13. The discussion includes the governing principles of performance parameters like adsorption, diffusion, acidity and how these parameters fundamentally influence zeolite catalysis. Brief descriptions of the elementary steps of hydrocarbon conversion over zeolites are also given. The intent is not to have an extensive review of the field of zeolite catalysis, but to select a sufficiently large subset of published literature through which key points can be made about reaction mechanisms and zeolitic requirements. 

That products of intermediate oxidation level can be detected in the photocatalytic reactions of hydrocarbons and fossil fuels is also consistent with a surface bound radical intermediate . Photocatalytic isotope exchange between cyclopentane and deuterium on bifunctional platinum/titanium dioxide catalysts indicates the importance of weakly adsorbed pentane at oxide sites. The platinum serves to attract free electrons, decreasing the efficiency of electron-hole recombination, and to regenerate the surface oxide after exchange. Much better control of the exchange is afforded with photoelectrochemical than thermal catalysis > ) As before, hydrocarbon oxidations can also be conducted at the gas-solid interface... 

Autoxidation. In this category, which refers to direct reactions of substrates with oxygen, there are numerous examples of metal catalysis of hydrocarbon oxidation. While metal participation most frequently involves catalysis of hydroperoxide decomposition (21, 22) (Reactions 12 and 13),... 

A redox mechanism for oxidation catalysis was proposed by Mars and van Krevelen (34) for the oxidation of aromatics over V205. This mechanism introduced the concept that lattice oxygen of a reducible metal oxide could serve as a useful oxidizing agent for hydrocarbons. Moreover, it formed the basis for the early work at SOHIO which led to the development of the bismuth molybdate catalyst. Since that time there have been many reports which support the redox concept. 

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