Synthesis of Microporous/Mesoporous Core-Shell Materials with Crystalline Zeolitic Shell and Supported Metal Oxide Silica Core

KYOUNGSOO KIM; KLEITZ, FREDDY; NIMA MASOUMIFARD; ARNAL PABLO M.; SERGE KALIAGUINE

CRYSTENGCOMM

ROYAL SOC CHEMISTRY

Lugar: CAMBRIDGE; Año: 2016 vol. 18 p. 4452 - 4464

1466-8033

An engineered material, possessing a hierarchical porosity in a shape selective manner, was synthesizedby placing a microporous silicalite-1 shell over silica microspheres embedding various guest species. Corematerials were prepared by dispersing catalytically important metallic species, comprising Co, Mn or Ti,within the mesoporous structure of silica microspheres with different particle and pore sizes. Theconnectivity of the micro- and mesopore networks and shell integrity of the final core@shell products werestudied as the main quality control criteria by varying synthesis parameters, such as core pre-treatmentswhich include surface modification, seeding and calcination steps and the number of secondaryhydrothermal treatments. Depending on the core size and the presence of the guest species, themesoporous silica microspheres which contain guest species need an additional treatment of chemicalfunctionalization of the external surface with species such as (3-aminopropyl)triethoxysilane, rather thanusing a simple surface modification with ionic polymers. It is believed that using such chemical treatmentcan strengthen the adhesion of the seeds to the core surface by providing some additional silanol groupsand facilitating hydrogen bonding interactions. It is also shown that depending on the core size, two to fourshort hydrothermal treatments are required to turn the coated seed crystals into a uniform intergrown shellof silicalite-1 around mesoporous silica microspheres and to avoid aggregation and core dissolution. Suchmaterials with a molecular sieve crystalline shell can be used in a wide variety of applications, particularlyfor shape-selective adsorption and catalysis purposes.