Preparation of new zeolite membranes: Hydrothermal synthesis and characterization of vanadium-Silicalite-1

摘要

New transition metal-containing zeolite membranes, which have peculiar catalytic and separation properties, are very attractive as new materials. rnIn this paper the syntheses, crystallization kinetics, characterization of V-Silicalite-1 crystals and in situ hydrothermal seeded syntheses of V-Silicalite-1 zeolite membranes prepared from fluoride gels on various supports are reported. The effects of varying of single component amounts, pH and vanadium sources in the reaction mixtures on the kinetic parameters, on the gel preparation and on the properties of the final products are discussed rnThe general molar composition of the reaction mixture was 10SiO2:xVOSO4:yV2O5:qMF:1.25TPABr:wTPAOH:330H_2O, where 0.1 < x < 1.0; 0.05 < y < 0.5 , 0.0 < w < 1.25; M = NH4, Na or K and 1.0 < q < 10.0. Analyses of relative crystallinity values versus reaction times obtained varying the vanadium amount and sources reveal that increasing vanadium concentration in the reaction mixture decrease the reaction rate. Aspect ratio of different samples synthesized were analyzed and compared with Silicalite-1 crystals obtained in the same conditions but in absence of vanadium atoms. Composite zeolite membranes on various porous supports were prepared by hydrothermal syntheses involving seeded gels and/or supports and characterized by a variety of techniques including XRD, SEM, EPR and single gas permeation. rnConclusions rn1)The synthesis of V-Silicalite-1 crystals is influenced by pH value of the reaction mixture and by vanadium and fluoride amount in the reaction mixture; rn2)Vanadium atoms entry in the zeolite framework of V-Silicalite-1; rn3)Composite V-Silicalite-1 membranes can be prepared on various supports.