PREPARATION AND CHARACTERIZATION OF VANADOSILICATE, FERRISILICATE, AND GALLOSILICATE CATALYSTS IN THE PRESENCE OF FLUORIDE IONS

Abstract

Vanado-, ferri-, and gallosilicate catalysts were prepared from the mixtures containing colloidal silica, corresponding metal source, tetrapropylammonium bromide, and NH4F by hydrothermal crystallization at 175-degrees-C for 7 days. The pH value of the reaction mixture was low (pH < 8) compared to the conventional methods. The metal compounds have higher solubilities in these conditions than conventional conditions (pH > 10). The size distribution and the size of final products were found to be more homogeneous and larger than those of metallosilicates prepared in strong alkaline media. The characterization of metallosilicates with IR, X-ray diffraction, SEM, EPR, and Si-29 MAS NMR, indicated that corresponding metal atoms were successfully incorporated into the tetrahedral lattice sites of the ZSM-5 structure.