Hydrogen transfer to olefins

It can also undergo successive cracking reactions leading finally to B, or cracking reactions and hydrogen transfer to olefinic cracking products with formation of C and D. 

In most of the reactions catalyzed by zeolites, coking occurs mainly inside the pores. Since the size of the intermediates and transition states involved in the formation of coke molecules is close to the size of the space available near the acid sites (cavities, channel intersections) steric constraints will necessarily limit the formation of these intermediates. The significance of these constraints depends not only on the relative size of the intermediates and cavities but also on their shape. These constraints explain why in catalytic cracking the zeolites yield less coke than silica alumina hydrogen transfer to olefinic products occurs rather from naphthenes than from bulky coke precursors 18]. Moreover in alkane cracking the... 

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