Nuclear magnetic resonance study of the dealumination of an amorphous silica–alumina catalyst

Abstract

The ²⁹Si MASNMR and ²⁷Al NMR study of an amorphous silica–alumina catalyst and of its dealuminated forms suggests that the tetrahedral aluminium (Al^IV) is involved in Q⁴[Si(1Al)], Q⁴[Si(2Al)] and possibly Q³[(SiO)₂(AlO)SiOH] units. Species Q⁴[Si(0Al)] are also evidenced. Ca. 30% of the Al is tetrahedral and 70% octahedral (Al^VI) in the starting material. Upon dealumination, Al^VI is removed first, then Al^IV. The extraction of Al generates hydroxyls in Q³[(SiO)₃SiOH] and Q²[(SiO)₂Si(OH)₂] units.