MFI Titanosilicate Nanosheets with Single-Unit-Cell Thickness as an Oxidation Catalyst Using Peroxides

Abstract

Titanosilicate MFI (a three-letter structural code among ∼200 zeolite framework codes) nanosheets of single-unit-cell thickness were synthesized with a diquaternary ammonium surfactant as the zeolite structure-directing agent, that is, C16H33–N+(CH3)2–C6H12–N+(CH3)2–C6H13. The resultant titanosilicate nanosheet possessed a large intersheet mesopore volume with high surface area due to the nanomorphic crystalline architecture as well as the isomorphically incorporated titanium species. Thus, it exhibited notable catalytic activities with high epoxide selectivity for bulky molecular epoxidation reactions using H2O2 or t-butyl hydroperoxide as an oxidant. In addition, the catalytic performance could be enhanced via postsynthetic fluoride treatment with NH4F that can reduce the surface silanol groups and, hence, increase the surface hydrophobicity.

Hierarchically Nanoporous Zeolites and Their Heterogeneous Catalysis: Current Status and Future Perspectives

“…1-2 mol% Ti in the siliceous framework with nanosheet morphology. This catalyst exhibited very active and selective catalytic epoxidation for both small olefin such as 1-hexene and bulky cyclic olefins such as cyclohexene and cyclooctene using H 2 O 2 as an oxidant [134]. The high catalytic activity and selectivity to epoxide indicates that the Ti atoms were isomorphously substituted in the tetrahedral framework, as coordinated by four -OSi.…”

Mesostructured Zeolites

“…Transition metals exhibiting redox properties were reported to be incorporated into the MFI ultrathin framework, using C 16-6-6 (OH) 2 surfactant as a mesopore SDA [ 180 ]. Titanosilicate MFI nanosheets were suitable for the epoxidation of bulky cyclic olefi ns (e.g., cyclohexene and cyclooctene), displaying enhanced catalytic activity compared to TS-1.…”

“…Titanosilicate MFI nanosheets were suitable for the epoxidation of bulky cyclic olefi ns (e.g., cyclohexene and cyclooctene), displaying enhanced catalytic activity compared to TS-1. External Ti sites exhibited lower catalytic activity for the epoxidation of terminal alkenes, such as 1-hexene [ 180 ]. Higher catalytic activity was later obtained with a highly crystalline lamellar titanosilicate in the epoxidation of various bulky alkenes (e.g., 1-hexene, cyclohexene, cyclooctene, and cyclododecene) in the presence of tert-butyl hydroperoxide, cumene hydroperoxide, or aqueous H 2 O 2 [ 181 ].…”

Two-stage dual template alkali metal-free synthesis of micro-mesoporous aluminosilicates based on ZSM-5 zeolite precursors

“…Using of bifunctional polyammonium surfactants «Gemini-type surfactants» as structure directing agents (templates) with two or more quaternary nitrogen atoms (promoting the zeolite formation) connected with C 3 -C 6 alkyl bridges, as well as with one or two terminal hydrophobic (C 16 -C 22 ) alkyl groups limiting the growth of zeolite crystals and forming a mesostructure is one of the most promising and original approaches for obtaining of micro-mesoporous materials of zeolite type [9,10]. Using this method the analogues of a number of known zeolites (MFI, BEA, MOR, FAU and others) with so-called hierarchical porosity, different morphology (nanoparticles [11], nanolayers [9], nanorods [12]), structural and sorption characteristics inherent to zeolites and mesoporous molecular sieves (MMS), in particular-significant predominance of relatively large mesopores with diameter of 5-15 nm [11,13] and high (up to 0.6) accessibility index of acid sites for large molecules of organic substances [11,14] were obtained.…”