Chemisorption of propene on HZSM-5 by ultraviolet and infrared spectroscopy

Generation of alkenyl carbocations from propene in HZSM-5, containing Brønsted and Lewis acidity, has been investigated by u.v.–visible and i.r. spectroscopy. The band observed upon adsorption of propene in the range 1505–1540 cm–1 can be assigned to the CCC stretching mode of the allyl part of alkenyl carbocations. This conclusion agrees with the evidence from the u.v. method that monoenyl, dienyl and trienyl carbonium ions are formed by oligomeric processes. It is suggested that both types of acid centres are involved in the transformation of propene into oligomeric ions.