Zeolite Confined Ti(OH)4 Nanoparticles in Highly Active and Selective Oxidation Catalyst

Abstract

Some highly active, hydrophilic, MFI structured titanium silicate catalysts are characterized by an intense UV absorption centered in the 213-233 nm (43000-47000 cm -1 ) range. The assignment of this band to a specific molecular structure has remained unclear unlike the well published \213 nm charge transfer excitations between the 2p lattice oxygen orbitals and the 3d orbitals of isomorphously inserted, isolated, tetrahedral Tiatoms in TS-1 and the [233 nm UV bands of higher coordinated Ti-atoms at lattice defects or in variously agglomerated extra lattice Ti x O y (OH) z species. To decipher the structural origin of this intermediate UV band, we used Time-Dependent Density Functional Theory (TD-DFT) to compute the UV spectra of various model compositions and show in this paper that only one model, in which isolated tetrahedral Ti(OH) 4 molecules reside in the zeolite channels without any covalent bond to the framework, fits the experimental UV spectrum. Hence these confined tetrahedral Ti(OH) 4 nanoparticles may account for the enhanced activity and selectivity of some MFI type titanium silicate catalysts.

Dielectric properties and lattice dynamics ofα-PbO2-type TiO2: The role of soft phonon modes in pressure-induced phase transition to baddel

“…This soft-phonon-mode-based mechanism was further confirmed by results of our molecular dynamics (MD) simulation of α-PbO 2 -type TiO 2 which was carried out at experimental conditions of 300 K and 37 GPa. 17 The MD simulation was implemented by the "General Utility Lattice Program"(GULP) package 42 with an NPT ensemble using the Dreiding empirical force potential, 43 which has previously been adopted in simulations of molecular adsorption on the TiO 2 surface, 44 zeolite-confined Ti(OH) 4 nanoparticles, 45 and other surfactant interactions at mineral surfaces. 46 The Nosé-Hoover thermostat was applied to control the temperature.…”