TY - JOUR
T1 - Elucidating the local environment of Ti(IV) active sites in Ti-MCM-48
T2 - A comparison between silyted and calcined catalyst
AU - Pea, M. L.
AU - Dellarocca, V.
AU - Rey, F.
AU - Corma, A.
AU - Coluccia, S.
AU - Marchese, L.
N1 - Funding Information:
The authors thank Dr. E. Gianotti for assistance during FTIR and DR UV–Vis–NIR measurements. Financial supports from Italian MURST (Ministero dell'Università e della Ricerca Scientifica e Tecnologica), MAT97-1207-CO3-01 and MAT97-1016-CO2-01 Spanish projects and the Italy–Spain bilateral action HI1998-0101 are acknowledged. M.L.P thanks the Ministerio de Educación y Cultura for the Doctoral fellowship.
PY - 2001/6
Y1 - 2001/6
N2 - A mesoporous Ti-MCM-48 material was silylated using hexamethyldisilazane (HDMS) and a remarkable increase in the catalytic performances in the cyclohexene epoxidation with tert-butylhydroperoxide obtained. We report on a combined FTIR, diffuse reflectance UV-Vis-NIR, photoluminescence and 29Si MAS NMR study, augmented by TGA and XRD analysis, of the local environment of Ti sites in both calcined and silylated Ti-MCM-48 catalysts. Spectroscopic studies were also performed on the as-synthesised material and showed that both silanols and titanols are formed during the decomposition of the cetyltrimethylammonium hydroxide surfactant used to template the mesoporous structure. Unequivocal evidences that a further silica condensation of the MCM-48 framework structure occurs both during thermal treatments in vacuum and after calcination at 540°C are also reported. Upon silylation, a more hydrophobic surface is obtained where trimethylsilyl groups (Si(CH3)3) are anchored on to the silica surface by reaction of the silylating agent, HDMS, with silanols, and in addition, (SiO)33)TiOH sites transformed into (SiO)3 TiOSi(CH3)3. It is proposed that the more hydrophobic character of the silylated material prevents the deactivation of the catalyst by decreásing the amount of glycols which may be formed by reaction of the epoxide with water adsorbed on the surface of the Ti-MCM-48, and that poison the titanium catalytic centres.
AB - A mesoporous Ti-MCM-48 material was silylated using hexamethyldisilazane (HDMS) and a remarkable increase in the catalytic performances in the cyclohexene epoxidation with tert-butylhydroperoxide obtained. We report on a combined FTIR, diffuse reflectance UV-Vis-NIR, photoluminescence and 29Si MAS NMR study, augmented by TGA and XRD analysis, of the local environment of Ti sites in both calcined and silylated Ti-MCM-48 catalysts. Spectroscopic studies were also performed on the as-synthesised material and showed that both silanols and titanols are formed during the decomposition of the cetyltrimethylammonium hydroxide surfactant used to template the mesoporous structure. Unequivocal evidences that a further silica condensation of the MCM-48 framework structure occurs both during thermal treatments in vacuum and after calcination at 540°C are also reported. Upon silylation, a more hydrophobic surface is obtained where trimethylsilyl groups (Si(CH3)3) are anchored on to the silica surface by reaction of the silylating agent, HDMS, with silanols, and in addition, (SiO)33)TiOH sites transformed into (SiO)3 TiOSi(CH3)3. It is proposed that the more hydrophobic character of the silylated material prevents the deactivation of the catalyst by decreásing the amount of glycols which may be formed by reaction of the epoxide with water adsorbed on the surface of the Ti-MCM-48, and that poison the titanium catalytic centres.
KW - Epoxidation catalst
KW - Silylation
KW - Spectroscopic studies
KW - Ti-MCM-48
UR - http://www.scopus.com/inward/record.url?scp=2342658193&partnerID=8YFLogxK
U2 - 10.1016/S1387-1811(01)00201-3
DO - 10.1016/S1387-1811(01)00201-3
M3 - Article
SN - 1387-1811
VL - 44-45
SP - 345
EP - 356
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
ER -