EFFECT OF ALUMINUM AND GALLIUM CONCENTRATION ON THE CRYSTALLIZATION RATE OF TPA MFI ZEOLITES SYNTHESIZED WITH MENH(2) IN THE ABSENCE OF INORGANIC CATIONS/

The synthesis of [M]-ZSM-5 zeolites (M = Ga, Al, Ga + Al) in the absen ce of inorganic cations and with tetrapropylammonium (TPA) as a templa te agent and methylamine (MA) as a complexing and mobilizing agent, wa s carried out at 185 degrees C, under autogenous pressure and rocking agitation, using a low reactive aerogel. The samples were characterize d by XRD, i.r., SEM, and Al-27 and Ga-71 MAS n.m.r. The results show t hat the efficiency of the aluminum and gallium addition into the zeoli te structure is almost 100%, but the morphology and the size of the cr ystals as well as the crystallization rate of the zeolites are modifie d by the chemical composition of the synthesis gel. The presence of al uminum strongly reduces the crystallization rate of metallosilicates w ith MFI-type structure. The higher the concentration of aluminum, the higher the decrease. This might be related to the lower stability of t he aluminum monomeric species.