Re-investigation of titanium silicalite by X-ray absorption spectroscopy: Are the novel titanium sites real?

Ti Location in the MFI Framework of Ti−Silicalite-1: A Neutron Powder Diffraction Study

“…The obtained distances are very close to those experimentally found by EXAFS experiments on well-manufactured TS-1 samples. [19][20][21][22]24,25 The authors conclude that, among the 24 different T sites, no clear preferential site was emerging from the energy calculation. Millini et al 27 reached the same conclusion concerning orthorhombic MFI on the basis of local density functional quantum mechanical calculations on pentameric Ti(OSiO 3 H 3 ) 4 cluster.…”

“…The obtained Ti-O distance (1.80 Å) was in full agreement with EXAFS data. 19,[20][21][22]24,25 Oumi et al 31 investigated the isomorphic substitution of Ti into the orthorhombic MFI framework using a molecular dynamics (MD) approach. The interesting result of their work is the claim that the lattice parameter expansion along the three crystallographic axes is related to a specific substituted site.…”

“…11 On the other hand, the possibility of Ti distribution into different sites, resulting in a linear combination of the corresponding ∆a, ∆b, and ∆c values, has not be considered by the authors and the equilibrium Ti-O distance reported by Oumi et al 31 (1.85 Å) is substantially larger than the experimental value observed by EXAFS. [19][20][21][22]24,25 In a subsequent MD work Smirnov and van de Graaf 32 did not found any correlation between the unit cell expansion and the Ti location. More recently, Njo et al 33 reported a study based on combined Metropolis Monte Carlo and molecular dynamics.…”

Ti XAS of a Novel Cs–Ti Silicate

“…Recently, questions of Ti valence and coordination in zeolitic materials have been addressed using the analysis of the XANES and EXAFS spectra (4)(5)(6)(7)(8)(9). Some researchers have reported some difficulty in determination of Ti coordination number (4,8,10). In this work, several Ti standards, a Cs standard and two CsTiSi O samples prepared with different heat treatments were analyzed.…”

Oxidación selectiva de hidrocarburos sobre tamices moleculares de poro grande conteniendo titanio.

“…Los primeros estudios sobre la TS-1, basados en la comparación del espectro XANES con el de otros compuestos donde la coordinación del Ti es bien conocida, revelaron la presencia de especies con coordinación entre 4 y 6. Estudios más recientes 71,72 sobre muestras deshidratadas confirman la coordinación tetraédrica de los centros de Ti justificando los datos anteriores por la existencia de especies extrarred y al efecto de la hidratación de las muestras analizadas. El demostraron, por cálculos teóricos, la inestabilidad de dichas especies.…”