Reactions of methylpropene-2- 13C on H-mordenite : III. Effect of catalyst pretreatment

Abstract

Reactions of 2-methylpropene-2- 13C have been carried out at 120 °C on a series of deammoniated mordenite samples activated at various temperatures (120 to 780 °C). Although each reaction product had the same characteristic labeling as H-mordenite, significant changes in product distributions have been observed when increasing the activation temperature. Trimethylpentenes (TMP), obtained by cationic dimerization, are formed on ammonium mordenite and their amounts increase only by a factor of 1.5 on zeolites activated at 450 °C. At activation temperatures T a ranging from 450 to 800 °C, the decrease in production of TMP parallels closely the decrease in proton concentration, as determined by NaCl ion exchange titration. The amounts of dimethylhexenes, C 5C 7 hydrocarbons and hydrocarbon residues increase sharply by a factor of 4 at activation temperatures of 350–400 °C, then reach a flat maximum and drop rapidly above T a = 500 °C. The observed increase in activity is interpreted by the generation at 400 °C of Lewis sites, allowing formation of a hydrocarbon chain attached to the zeolite framework, and it is suggested that structural changes in the zeolite, arising during the first stages of ultrastabilization, account for the rapid drop of activity beyond 500 °C.