Titanosilicate Molecular Sieve for Size-Screening Photocatalytic Conversion

Abstract

Titanosilicate molecular sieves, when activated by ultraviolet light irradiation in water in the presence of molecular oxygen, catalyze a conversion of molecules having a size close to the pore of the catalysts but are inactive for molecules having much larger or smaller size. This unprecedented size-screening photocatalytic activity is triggered by a combination of H2O-induced shortened lifetime of active species (charge-transfer excited state of tetrahedrally coordinated titanium oxide) and restricted diffusion of a molecule inside the pore. This catalytic property demonstrates a potential utility of the catalyst for selective transformation of molecules that is associated with a size reduction of molecules, so-labeled "molecular shave" transformation.

A surface science perspective on TiO2 photocatalysis

“…Tetrahedral Ti 4+ in frameworks: In contrast to supported tetrahedral Ti 4+ , there are several examples of tetrahedral Ti 4+ sites that have been built into supporting frameworks of zeolites [1607,1608] or of mesoporous/nanoporous systems [1476,[1609][1610][1611][1612][1613][1614]. The Anpo group [33,1615] is a leader in exploration of the photocatalytic activity of tetrahedral Ti 4+ in zeolite systems, particularly in the settings of CO 2 photoreduction [1186,[1616][1617][1618][1619][1620][1621][1622] and NO photoreduction [1164,1165,1372,[1623][1624][1625].…”

Selective photocatalytic degradation of aquatic pollutants by titania encapsulated into FAU-type zeolites

“…Therefore, the hybrid photocatalysts with all inorganic components are highly desired. For example, titanosilicate molecular sieves such as ETS-4, ETS-10 and TS-1 were employed for the shape-selective photocatalysis [15][16][17]. However, their photocatalytic activities were low because of the low content of titanium.…”

Titanium Oxide-based Photocatalysts for Selective Organic Transformations

“…The combination of isolated Ti oxide species and the zeolite pores (～0.6 nm) shows a "size-screening" photocatalytic activity that promotes selective conversion of molecules having a size close to the pore of the catalyst 29) . This is achieved by titanosilicate molecular sieve containing isolated Ti-oxide species, such as titanium silicalite-1 [TS-1; MFI structure; pore dimensions, 0.54 nm 0.56 nm (sinusoid channel) and 0.52 nm 0.58 nm (straight channel)] and titanium silicalite-2 (TS-2; MEL structure; 0.53 nm 0.54 nm).…”