Al-MCM-41: its acidity and activity in cyclohexene conversion

Investigation of cyclohexene conversion over Al-MCM-41 has shown that the c oncentrations of Bronsted and Lewis acid sites increase with the Al content of the materials. The conversion follows mainly two mechanisms: cyclohexen e skeletal isomerisation (CSI) and hydrogen transfer (HT). The products wit h 6 carbon atoms in a molecule prevail in all cases. Some amounts of produc ts with 1 to 8 carbon atoms are also formed as a result of cracking or alky lation. All these reactions can occur at the acidic centres of the catalyst s. The process of conversion, proceeding over the Bronsted acid sites, resu lts in the formation of coke deposits in addition to volatile products. The amount of coke decreases with increasing reaction temperature and decreasi ng Al content of the material. The deposits cause a decrease in the effecti ve concentrations of both the Bronsted and Lewis acid sites. Thermodesorpti on of pyridine has shown that (i) the concentrations of the Bronsted and Le wis acid sites before and after the conversion processes differ only slight ly and (ii) the acidic strength of the Bronsted sites is almost independent of their concentration and the Si/Al ratio.