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

The 29Si MASNMR and 27Al NMR study of an amorphous silica–alumina catalyst and of its dealuminated forms suggests that the tetrahedral aluminium (AlIV) 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 (AlVI) in the starting material. Upon dealumination, AlVI is removed first, then AlIV. The extraction of Al generates hydroxyls in Q3[(SiO)3SiOH] and Q2[(SiO)2Si(OH)2] units.