Molecular sieves of faujasite structure

The present invention relates to a process for preparing molecular sieves of faujasite structure and to the pre-shaped molecular sieve bodies prepared according to the present process. More specifically, the present invention relates to a process for preparing molecular sieves of faujasite structure which comprises contacting a precursor gel with steam, optionally followed by caustic washing, said process making it possible to form a zeolite of faujasite structure in pre-shaped bodies. A process for preparing molecular sieves of type Y faujasite structure is described, as well as pre-shaped bodies of faujasite structure type Y molecular sieves. The process comprises preparing a precursor gel from a source of silica-alumina or a source of alumina and a source of silica with a template agent at a SiO/AlOgreater than 7 and suitable for forming a type Y zeolite, drying the precursor gel and contacting the dried precursor gel with steam, optionally followed by caustic washing, without the formation of crystalline phases other than type Y zeolite being observed. Advantageously, the pre-shaped bodies prepared with the precursor gel of Y zeolite, when subjected to the process of the invention, will have their outer surface covered by type Y zeolite crystals. The molecular sieves so obtained may be employed as catalysts or adsorbents in various processes of the chemical or oil industry.