Some Major Polystep Reactions of Hydrocarbons

A number of hydrocarbon transformations have been shown by Haensel and Donaldson 10), Heinemann et al. 11), and by Ciapetta and Hunter 12) to be catalyzed by solid catalysts in which a transition metal, notably platinum or nickel, has been combined with an acidic oxide carrier substance such as, for example, silica-alumina, or halogen containing alumina. These include the isomerization of paraffins, the hydroisomerization of naphthene rings, and the hydrogenative cracking of paraflBns. 

Mills et al. IS) proposed formal reaction schemes in which conversion proceeds through olefinic reaction intermediates, such as the one illustrated by Fig. 10 for the Ce-hydrocarbons. They introduced the concept of separate catalytic functions, in terms of an isomerization activity—operative on the olefinic intermediate—associated with the acidic oxide base and a hydrogenation activity associated with platinum. Ciapetta and Hunter 

Mills et al. (IS) proposed that (see Fig. 10) in order to travel to a compound in a diagonal position, it is necessary to transfer on the catalyst surface from one site to another. Thus the concept of the dual functional hydrocarbon conversion catalyst with distinctly different sites became clearly introduced. 

In the author s laboratory, extensive studies were undertaken not only to examine the reaction schemes proposed by Mills et al., but specifically to test the feasibility of catalytic cooperation by chemically unconnected, i.e., physically separate, catalytic components, wherein the intermediates are true gas phase species coupling the catalyst components through mass transport following the classical laws of gaseous diffusion, in hne with the principles and characteristics discussed in the preceding sections. Experimental work that makes use of physically distinct catalytic materials or components constitutes the most direct route to the testing and study of true polystep reaction mechanisms. 

The feasibility of coupling through the diffusion process was briefly reported by Weisz (14)- Experimental evidence of the cooperative action of catalyst mixtures was mentioned by Mills (15) and Weisz (16) at the First International Congress on Catalysis, and brief reports have appeared by Weisz and Swegler (17), Hindin et al. 18), and Weisz 19). 

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