Hydrocarbon oxidation over

A redox mechanism involving lattice oxygen originally proposed in 1954 by Mars and Van Krevelen (22) for hydrocarbon oxidation over V2O5 can be applied to a variety of catalytic oxidation reactions (23). The following illustrates a lattice redox mechanism for CO oxidation ... 

The effect of lead on hydrocarbon oxidation over noble metal catalysts has been variously presented as a relation between catalyst activity and lead content in gasoline (19, 22), or of lead supplied to the engine (31, 32), etc. The most meaningful correlation is between hydrocarbon activity and lead deposit on the catalyst. Two examples of such correlations, one for laboratory-tested samples and the other for fleet-tested catalysts, will follow. 

Studies of the activity and selectivity of tin-antimony oxides for the oxidation of propylene to acrolein have been reviewed by Hucknall (6), and more recent investigations of hydrocarbon oxidation over the catalyst have been described by Higgins and Hayden (7). In this article only those studies that are directly relevant to the fundamental properties of the catalyst will be reexamined. 

Our previous studies concerning hydrocarbons oxidation over transition metal oxides allowed us to conclude that most hydrocarbon molecules are activated at their weakest C-H bond by oxidation occurring at the expense of high-oxidation-state transition metal cations exposed at the catalyst surface, giving rise to surface alkoxides [8]. It is likely that this also occurs on the surface Fe cations on Mg-ferrite surfaces, with a mechanism that can be described as in the following scheme. 

These reactions play an extremely important role in hydrocarbon oxidation over the temperature range discussed here, and in some cases even small variations in their parameters can lead to serious deviations in the simulated kinetics. 

The working out of an explicit scheme for hydrocarbon oxidation over various catalysts was hindered until lately due to insufficient development of the theory and to lack of extensive experimental data. 

A characteristic feature of hydrocarbon oxidation over Cu20, V206,... 

P. B. Venuto (Mobil Oil, Paulsboro, N. J.) Do you think that the lack of selectivity in hydrocarbon oxidation over the Co-zeolite to which you alluded in your paper may derive from (conventional) free radical chains initiated by cobalt cations located at or near the crystal external surface ... 

C. F. Cullis and B. M. Willatt, "The Inhibition of Hydrocarbon Oxidation over Supported Precious Metal Catalysts", J. Catal. 1984, S6, 187-200. 

However, the kinetics of CO and hydrocarbon oxidation over platinum has a negative first order dependence on CO concentration for most of the ranges of temperature and concentration of interest to automotive catalysis. Voltz et ah (I) demonstrated that, under a total pressure of 1 atm. at 400°-800°F, the kinetics depend inversely on CO concentration from 0.2% to 4%. Therefore, when there are diffusion effects, a decline in CO concentration toward the interior of a porous catalytic layer would lead to an increase in reaction rates in the interior. Diffusion then has a beneficial rather than a detrimental effect on overall kinetic rates, and a thick catalytic layer may effect a higher conversion than a thin layer under identical ambient conditions. 

Culhs, C. and WiUatt, B. (1984). The inhibition of hydrocarbon oxidation over supported precious metal catalysts, J. Catal., 86, pp. 187-200. 

Selective Conversion of Methane to Ci Hydrocarbons using Carbon Dioxide as an Oxidant over CaO-MnO/CeOi Catalyst... 

Synthesis gas generation Process in which light hydrocarbons are partially oxidized over a catalyst at about 875 K with oxygen and the carbon monoxide is shifted with steam to produce CO and H. ... 

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. 

Over the years, there have been many proposals regarding factors that determine selectivity in hydrocarbon oxidation [1-6]. Basically, the formation a certain product can be categorized by two factors how many oxygen atoms are incorporated into the reactant and where in the molecule are they incorporated. The ability to control these two factors determines whether one can control the observed selectivity. 

Fio. 25. SCAT light off comparison of the activity of different hydrocarbons for oxidation over a Pt-based DOC. All hydrocarbons were present at the same concentration on a Ci basis. 

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