Investigating the Role of Zeolite Nanocrystal Seeds in the Synthesis of Mesoporous Catalysts with Zeolite Wall Structure

Abstract

Mesoporous titania-silica catalysts were prepared by hydrothermal conversion from synthesis solutions containing a zeolite structure directing agent (TPA+) and a porogen (CTA+). Syntheses were carried out with and without addition of zeolite seeds (i.e., TS-1 and Sil-1 nanocrystals). Catalysts prepared in the presence of zeolite nanocrystal seeds have greater proportions of tetrahedrally coordinated titanium, which correlate well with the detection of zeolite SBU fragments and ring-structure by TOF-SIMS and FTIR. The incorporation of titano-silicates and zeolite structural units in the mesopore walls could explain the better activity and stability of these catalysts (Ti-MT1 and Ti-MS1) compared to the catalyst prepared by the conventional method (Ti-MCM-41). The similarity in the reactivity of catalysts prepared from TS-1 and Sil-1 nanocrystal seeds dispels the idea that the seeds are merely a source of the zeolite fragments incorporated in the pore walls but instead suggests that the seeds play an active role to stabilize and promote the incorporation of SBU from the solution.

Synthesis of stable Ti-containing mesoporous tubular membrane using silicalite-1 nanoparticles as seeds

“…The permeability of the membranes was tested by a soap-film flow meter at room temperature. The benzene and styrene hydroxylation were carried out in a homemade reactor with details described elsewhere [8,44]. [45].…”

“…Pedernera et al [24] have reported that the inclusion of a zeolite precursor precursor during the mesoporous membrane synthesis led to partial zeolite incorporation into the porous structure. On the other hand, the Sil-1 particle seeds could promote the incorporation of zeolite secondary building unit fragments from the solution [44]. Therefore, the Sil-1 nanoparticles loaded on the support would be beneficial for embedding the zeolite units in the mesopore walls.…”

“…Consequently, this novel seeding method would be beneficial to prepare mesoporous membrane on different porous supports. Noteworthy is that the Sil-1 nanoparticles were homogeneous dispersed in the synthesis solution for mesoporous powder synthesis [44], while the Sil-1 seeds were attached on the alumina supports for mesoporous membrane in this work. Thus, the incorporation of zeolitic structure fragments into the mesopore walls from supported Sil-1 seeds maybe was much more complicated and difficult.…”

“…The results showed that the TS-1 films prepared from Sil-1 seeds had comparable structure and catalytic activity to the films prepared from TS-1 seeds. In our more recent study [44], the Sil-1 nanoparticle seeds were further used to assemble the mesoporous Ti-containing zeolite catalyst. It has been found that the presence of Sil-1 nanocrystal seeds induced the growth of zeolite secondary building unit (SBU) fragments and ring-structure in the walls with more zeolitic tetrahedrally coordinated titanium in the framework [44].…”

“…In our more recent study [44], the Sil-1 nanoparticle seeds were further used to assemble the mesoporous Ti-containing zeolite catalyst. It has been found that the presence of Sil-1 nanocrystal seeds induced the growth of zeolite secondary building unit (SBU) fragments and ring-structure in the walls with more zeolitic tetrahedrally coordinated titanium in the framework [44]. This led to the better structure stability and activity compared to the conventional prepared Ti-MCM-41.…”