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Silica alumina co-gels

A new class of hi alumina silica-aluminas has been prepared with hi pore volume and with controllable pore size. For 20 wt % Si02 content materials steam treatment at 760°C serves to substantially increase the gas oil cracking activity. Steam stability at 870°C has also been demonstrated for these unique materials. These samples are prepared by recrystallization of co-gels of aluminum and silicon alkoj compounds losing a two-step procedure. AmorjAious alumina shows similar physical properties to those of the silica-alumina co-gels vhen re-crystallized in an analogous manner. [Pg.97]

Most zeolites are synthesized from proportional mixtures of sodium aluminate and sodium silicate and, in some cases, colloidal silica. The procedure is different to that for the preparation of silica alumina catalysts because zeolites form under alkaline conditions as the silica/alumina co-gel crystallizes in the presence of hydroxyl ions. The zeolite type formed depends on the proportion of silicate and aluminate in the solution and the reaction temperature and pressure. The time taken for zeolite crystals to form can range from a few hours to several days. Seeds or templates are often added to induce formation of the appropriate crystalline product. Knowhow is very important, and precise details for a specific preparation are not always published. [Pg.188]


See other pages where Silica alumina co-gels is mentioned: [Pg.140]    [Pg.97]    [Pg.254]   
See also in sourсe #XX -- [ Pg.134 ]




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