Process for the synthesis of a silica enriched crystalline aluminosilicate having the offretite structure, the aluminosilicate obtained and its use as a catalyst for the conversion of hydrocarbons

A process for the synthesis of dealuminated offretite without a major loss of crystallinity and which utilizes a treatment with a strong mineral acid, which process comprising the steps of:

• (1) preparing a nucleation gel A comprised of a mixture containing sources of silicon, aluminium, alkali metal ions (M), and an organic structuring agent (Z) and water,
• (2) allowing the mixture to age for a period of at least about 12 hours,
• (3) preparing a growth gel B comprised of a mixture containing a source of silicon, aluminium, alkali meal ions and water,
• (4) adding at least 2% by weight of aged gel A to fresh gel B to form a gel A-B mixture,
• (5) heating the gel A-B mixture with stirring to achieve crystallization, followed by separation, washing and drying of the crystals,
• (6) calcining said crystals at a temperature greater than about 500.degree. C. sufficient to remove the organic structuring agent,
• (7) replacing the alkali metal ions in said crystals by protons,
• (8) subjecting said crystals to hydrothermal treatment with 100% steam at a temperature of between about 500.degree. and 800.degree. C. for a period of less than 5 hours, and
• (9) treating said crystals with a strong mineral acid in an aqueous medium, followed by separation, washing and conditioning of the crystals.