Kinetics and Mechanism of Individual Hydrocarbon Reactions

In the preceding paragraphs we have discussed bifunctional catalysis from the standpoint of the nature of the catalyst surface as well as the kinds of reactions which take place and have summarized the results of certain critical experiments from which a mechanistic picture has evolved. With this background in mind, we will now discuss the results of kinetic studies in the following sections. 

As pointed out earlier, the dehydrogenation of cyclohexanes to aromatics over a supported platinum catalyst requires only platinum sites. The properties of the support do not appear to be critical, provided that the platinum is well dispersed. 

The conversion of cyclohexanes to aromatics is a highly endothermic reaction (AH 50 kcal./mole) and occurs very readily over platinum-alumina catalyst at temperatures above about 350°C. At temperatures in the range 450-500°C., common in catalytic reforming, it is extremely difficult to avoid diffusional limitations and to maintain isothermal conditions. The importance of pore diffusion effects in the dehydrogenation of cyclohexane to benzene at temperatures above about 372°C. has been shown by Barnett et al. (B2). However, at temperatures below 372°C. these investigators concluded that pore diffusion did not limit the rate when using in, catalyst pellets. 

A study of the kinetics of methylcyclohexane dehydrogenation to toluene in the temperature range 315 to 372°C. has been reported by 

Summary op Rate Data for Methylcyclohexane Dehydrogenation over Pt-AljOa (S6) 

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