ALKANE REARRANGEMENT PATHWAYS ON TELLURIUM-BASED CATALYSTS

Isotopic tracer studies and reaction pathway analyses suggest that olefins and diene and triene species are reactive intermediates in n-heptane dehydrocyclization on Te/NaX. Their concentration is limited by surface hydrogen overpressures caused by a rate-limiting hydrogen desorption step in the dehydrogenation sequence. The distribution of toluene isotopomers formed from dehydrocyclization of n-heptane-1-13C is consistent with a reaction sequence involving thermal cyclization of an equilibrated mixture of conjugated and nonconjugated heptatrienes. Methylhexanes are formed predominantly by methyl and ethyl shift reactions of heptenes, and not by hydrogenolysis of CS ring species. Alkane hydrogenolysis on Te/NaX occurs predominantly by thermal cracking pathways of n-heptane and heptenes. No catalytic function for either (1,5) or (1,6) ring closure was observed on Te/NaX; a catalytic dehydrogenation function, however, suffices for dehydrocyclization to occur with high selectivity. © 1990.