USE OF SHORT-CHAIN ALKYLAMINE AS COMPLEXING-MOBILIZING AGENTS - AN ALTERNATIVE TO THE FLUORIDE-ROUTE FOR THE SYNTHESIS OF ZEOLITE METALLOSILICATE CATALYSTS

A wide series of zeolite metallosilicates was successfully synthesized using a series of short alkyl chain amines as new potential mineraliz ing agents. In the particular case of ZSM-5 containing various framewo rk heteroatoms, the mobilizing-complexing role of methylamine, as comp ared to that of fluoride ions, can be very different and basically dep ends on the nature of the metallic ion. The relative strength of the v arious fluoro or amino complexes could be exploited to monitor and con trol the selective (simultaneous or successive) incorporation of vario us metallic species in the MFI framework. The incorporation, occurring in variable amounts, can be arbitrary considered as total (i.e. with more than 2 ionic species incorporated per MFI unit cell) for Zn2+, Al 3+, Ga3+, Fe3+, B3+ and Ti4+. Cd2+ and Cr3+ care only partly incorpora ted (M/u.c. < 2) while Cu2+, Co2+) Mn2+ and Mo5+ never incorporate the MFI lattice. Besides the fact that these ions do not readily achieve a tetrahedral coordination. the other possible reason could be that th eir polycondensation, if any possible, does not occur when these speci es are involved in too strong complexes with methylamine. In some case s (Cu2+, Fe2+, Ag+), methylamine behaves as a reducing agent in the sy nthesis medium and the corresponding metallic species are found admire d with silicalite. At similar complexing power, the (alkali-free) ''am ine route'' is preferred to the now more conventional ''fluoride route '', that involves lower pH and less supersaturated solutions, requirin g very long crystallization times. These latter can also be drasticall y reduced by using fluoride-amine admixtures.