Controlled Postgrafting of Titanium Chelates for Improved Synthesis of Ti-SBA-15 Epoxidation Catalysts

Abstract

A new synthesis procedure that is based on the grafting of titanium alkoxide species chemically modified by acetylacetone (acac) on the surface of a P123/SBA-15 composite material is proposed to prepare Ti-SBA-15 catalysts and studied by a combination of elemental analysis, Fourier transform infrared spectroscopy (FTIR), solid-state 13 C (CP) NMR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), diffuse reflectance UV-vis (DR-UV-vis), and N 2 physisorption at -196 °C. In the absence of the acac chelates, the observed formation of anatase TiO 2 onto the surface of the material demonstrates that the coordinating ligand acts as an inhibitor for the crystallization of anatase. Furthermore, FTIR and 29 Si NMR results show that the chelated titanium alkoxide precursor interacts strongly with the silanol groups, which, in turn, greatly enhances the dispersion of the titanium species in the mesoporous silica matrix. Moreover, a decrease of the temperature applied for the postgrafting and an increase of both the acac/Ti ratio and pH are shown to favor the retention of titanium on the materials surface without affecting the titanium dispersion. According to the X-ray photoelectron spectroscopy (XPS) results, a maximal titanium content of 13.8% can be well-dispersed on the surface of the mesopores without formation of an excess on the external surface of the solids. However, the results of the DR-UV-vis analyses and the catalytic epoxidation of cyclohexene reveal that the maximal concentration of titanium species in tetrahedral coordination is obtained for materials with a Ti/Si ratio of 5.6%. Even if materials with higher titanium content do not show higher conversion of cyclohexene, they do exhibit remarkably low catalytic deactivation during the recycling tests. A higher hydrothermal stability is suggested as an explanation for the lower deactivation of Ti-SBA-15 at high titanium content.

Multitechnique Investigation of Mesoporous Titanosilicate Materials Prepared from Both the Self-Assembly and the Liquid Crystal Mechanisms

“…It corresponds to coordinated Ti 4þ species that are incorporated into the silica framework. 15,23 The second contribution at 300 nm is blue shifted from the one of TiO 2 . This blue shift has been observed for titania nanoparticles 24,44,49 on silica and corresponds to small TiO 2 clusters through the quantum size effect.…”

Titanium-incorporated organic–inorganic hybrid adsorbent for improved CO2 adsorption performance

“…1(B)) with the single intense peak at about 23.3 (2u) accompanied by line broadening. For the materials modified by the titanium, the different lines associated with crystalline TiO 2 appeared in the XRD pattern [18]. As expected from the preparation process, a distinct peak at about 25.2 (2u) and three slightly weak peaks between 35 and 60 for Ti(0.2)-DMS, and only three weak peaks detected for Ti (0.1)-DMS, which reveal that the TiO 2 is of anatase structure (JCPDS: 01-083-2243) with no trace of other phases.…”

Hydrophobicity enhancement of Ti-MWW catalyst and its improvement in oxidation activity

“…During the past decades great efforts have therefore been concentrated on the synthesis and application of a variety of titanium zeolites and Ti-containing mesoporous materials with different structures and pore dimensions including TS-2 [7], Ti-MWW [8,9], Ti-MOR [10], Ti-MCM-38 [11], Ti-Beta [12][13][14], Ti-MCM-41/48 [15][16][17][18][19][20], Ti-SBA-15 [21][22][23] and Ti-containing polyhedral oligomeric silsesquioxanes (POSS) [24,25] and so on.…”