Process for the synthesis of zeolites of the ferrisilicate type, products so obtained

A process for the preparation of a crystalline synthetic zeolite comprising:

• (a) forming a reaction mixture having a pH less than about 10 comprising water, at least one source of silica, at least one source of ferric salt, at least one source of mobilizing agent containing fluoride ions, at least one source of templating agent which can provide organic cations or a mixture thereof,
• said reaction mixture having a composition, in terms of molar ratios, of:
• ______________________________________ SiO.sub.2 Fe.sub.2 O.sub.3 5-2000 Fluoride/SiO.sub.2 0.04-4 Organic cations/SiO.sub.2 0.04-2 H.sub.2 O/SiO.sub.2 6-500, ______________________________________
• (b) keeping said mixture at a temperature at most equal to about 250.degree. C. until a crystalline compound is obtained, and
• (c) calcining said compound at a temperature above 400.degree. C.

A zeolite produced by a process comprising:

• (a) forming a reaction mixture having a pH less than about 10 comprising water, at least one source of silica, at least one source of ferric salt, at least one source of mobilizing agent containing fluoride ions and/or at least one source of templating agent which can provide organic cations,
• said mixture having a composition, in terms of molar ratios, comprised within the following ranges of values:
• ______________________________________ SiO.sub.2 /Fe.sub.2 O.sub.3 5-2000 Fluoride/SiO.sub.2 0.04-4 Organic cations/SiO.sub.2 0.04-4 H.sub.2 O/SiO.sub.2 6-500 ______________________________________
• (b) keeping said mixture at a temperature of heating at most equal to about 250.degree. C. until a crystalline compound is obtained, and
• (c) calcining said compound at a temperature above 400.degree. C., whereby the resultant zeolite is a ferrisilicate zeolite of MFI structure, having:
• (i) the following approximate chemical formula:
• M.sub.2/n O, Fe.sub.2 O.sub.3, xSiO.sub.2
• wherein
• M represents a proton and/or a metal cation,
• n is the valence of said cation,
• (ii) an x-ray diffraction diagram shown in Table I of the accompanying specification, and
• (iii) a fluorine content of about 0.01% to 1.6% by weight.