Formation of radicals and catalytic activity of H-ZSM-5-type zeolites in unsaturated hydrocarbon conversions. PART 3. Olefin oligomerization and aromatization on parent and dehydroxylated H-ZSM-5

Abstract

The conversion of olefins on parent and dehydroxylated H-ZSM-5 has been studied. ESR techniques and UV-Vis-IR spectroscopy have been used for the comparative study of the formation of radicals and intermediates from different unsaturated compounds. It is shown that catalytic lowtemperature oligomerization of C3 H6 and i-C4H8 takes place on the outer surface of H-ZSM-5 crystals, whereas the high-temperature formation of aromatics takes place inside the zeolite channels. It is shown that the properties of redox sites do not change noticeably upon the transition from Brönsted acid sites to Lewis ones. Dehydroxylation of H-ZSM-5 results in suppression of the low-temperature transformation of sorbed olefins, but has a negligeable effect on the catalytic high-temperature conversion of olefins. © 1989.