Elementary Steps of Hydrocarbon Conversion over Zeolites

Elementary Steps of Hydrocarbon Conversion over Zeolites 

This section makes only brief remarks about some of the elementary steps of hydrocarbon conversion. More detailed analyses of these steps are done within the context of various reaction mechanisms. 

Mechanism for protonation of alkenes was previously discussed in Section 13.5.1. In general, protonation of alkenes is an exothermic process. Protonation of alkanes was discussed in Section 13.5.2. There wiU be further discussion on this step in Section 13.8.4 within the context of alkane cracking mechanisms. The formation of a penta-coordinated carbonium ion from alkane protonation is typically an endothermic process, the reverse being true for deprotonation. 

Methyl shift in carbenium ions is expected to require three elementary steps (ring closure, ring opening, hydride shift), enabling the positive charge to move 

Beta scission of a carbenium ion is an elementary step that is inihated by the weakening of the bond beta to the positive charge, leading to a smaller carbenium ion and an alkene. This elementary step is further discussed in Sections 13.8.1, 13.8.3.1 and 13.8.4 within the context of alkene skeletal isomerization, isobutane-2-butene alkylation and alkane cracking, respectively. 

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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. 

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