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The synthesis of [M]-ZSM-5 zeolites (M = Ga, Al, Ga + Al) in the absence of inorganic cations and with tetrapropylammonium (TPA) as a template agent and methylamine (MA) as a complexing and mobilizing agent, was carried out at 185°C, under autogenous pressure and rocking agitation, using a low reactive aerogel. The samples were characterized by XRD, i.r., SEM, and 27 Al and 71 Ga MAS n.m.r. The results show that the efficiency of the aluminum and gallium addition into the zeolite structure is almost 100%, but the morphology and the size of the crystals as well as the crystallization rate of the zeolites are modified by the chemical composition of the synthesis gel. The presence of aluminum strongly reduces the crystallization rate of metallosilicates with MFI-type structure. The higher the concentration of aluminum, the higher the decrease. This might be related to the lower stability of the aluminum monomeric species. |
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