Shuwu Yang

Formation of stable alkenyl carbenium ions in high yield by adsorption of 1-methylcyclopentene on zeolite Y at low temperature.

The formation of dimerized alkenyl carbenium ions, characterized by an IR band at 1513 cm-1 and a UV band at 323 nm, was observed by adsorption of 1-methylcyclopentene on HY and DY zeolites at temperatures as low as 150 K.

Adsorption, migration and reactions of hydrocarbons on zeolites observed by FTIR spectroscopy

The adsorption, migration and reactions of hydrocarbons on zeolites studied by FTIR spectroscopy are briefly reviewed. At low temperatures, alkyl-BAS (Brønsted acid sites) and π-BAS complexes were first formed before protonation of olefins. For 1-butene, it underwent double bond migration (DBM) to form cis- and trans-2-butenes. With increasing temperature, oligomerization occurred and resulted in highly branched dimer, e.g., 3,4-dimethyl-3-hexene. Compared with 1-butene, isobutene can oligomerize at much lower temperature and formed dimerized alkoxy species, even on isolated silanols of zeolites. Upon adsorption of cyclic olefins such as 1-methylcyclopentene, alkenyl carbenium ions were formed at temperatures as low as 150 K. The adsorption of butenes on ferrierite indicates the existence of energy barriers for their intercalation into the pores. The H/D isotope exchange reaction of alkanes with acidic hydroxyl groups of zeolites will also be discussed.