Infrared observation of the stable carbenium ions formed by adsorption of olefins on zeolite Y at low temperatures

摘要

The formation of alkenyl carbenium ions, characterized by an IR band at ca. 1510 cm-1, wassuccessfully observed by adsorption of 1-methylcyclopentene (MCPE), methylenecyclopentane(MECP) and 1-methylcyclopentanol (MCPOH) on faujasite zeolite. At temperatures as low as 150K, the carbenium ions were formed soon after introducing the olefins. The characteristic band at ca.1510 cm-1 increases in intensity with the elevation of temperature and is stable up to 373 K. ForMCPOH, the characteristic band appears at temperatures above 245 K after its dehydration. Theformed species were assigned to be dimerized alkenyl carbenium ions by calibrating the acid sites ofHY using 1-butene at 235 K. UV-vis spectroscopic studies confirm the formation of momoenylicand dienylic carbenium ions, with bands at 323 and 400 nm, respectively.