Ti-MCM

B.S. Uphade, M. Okumura, S. Tsubota, and M. Haruta, Effect of physical mixing of CsCl with Au/Ti-MCM-41 on the gas-phase epoxidation of propene using H2 and02 Drastic depression of H2 consumption, Appl. Catal. A 190, 43-50 (2000). 

In addition, the results of adsorption experiment in Fig. 4 revealed that H2O2 promotes the adsorption of 4-NP on the Cr-Ti-MCM-41 surface. From considering above results, it can be said that H2O2 increases the reaction rate by the promotion of adsorption of reactant and the removing of surface-trapped electrons. 

Fig. 2. Effect of HjOj (5mmol/L) on the photocatalytic decomposition of 4-NP (Co=25ppm) over Ti02/Cr-Ti-MCM-41 in visible light.

In this work, highly active epoxidation catalysts, which have hydrophobic surface of TS-1, were synthesized by the dry gel conversion (DGC) method. Ti-MCM-41 was synthesized first by a modifed method and the TS-l/MCM-41 catalysts were subsequently synthesized by the DGC method. The catalysts were characterized by the XRD, BET, FT-IR, and UV-VIS spectroscopy. TS-l/MCM-41 catalysts were applied to the epoxidation of 1-hexene and cyclohexene with aqueous H202to evaluate their activities for the epoxidation reaction. ... 

The TS-l/MCM-41 catalysts were synthesized in two steps [8]. The first step was involved with the preparation of TPAOH impregnate mesoporous materials and the second stq) was the DGC process. The TPAOH impregnated H-MCM-41 was prepare with calcine Ti-MCM-41, TPAOH (1 M solution of water) and ethanol under stirring by impregnation method. The parent gels were prepared with a TPAOH/Ti-MCM-41 ratio of 1/3 by weight. After 4 h, ethanol and water were removed in a rotary evaporator at room temperature and solid products were dried in a convention oven at 373 K for 48 h. The DGC process was carried out at 448 K for 3 h to obtain TS-1/MCM-41-A and for 6 h to obtain TS-1/MCM-41-B. However, the mesoporosity of Ti-MCM-41 was lost when the DGC process was carried out for 9 h. 

The XRD pattern of Ti-MCM-41 synthesized by the modified synthesis method is presented in Fig. 1, Here we observe more than three distinguishable peaks, which can be indexed to dififermt (hkl) reflections of hexagonal structure. These are the (100), (110), (200), and (210) peaks [5]. The highest intensity of (100) peak su ts that this material has a highly ordered hexagonal structure. 

The variation in the lattice vibration of the solid products was examined by utilizing the FT-IR technique at successive DGC process times and the results are presented in Fig. 5. The absorption bands at 550 cm and 450 cm" are assigned to the vibration of the MFI-type zeolite and the internal vibration of tetrahedral inorganic atoms. The band 960 cm" has been assigned to the 0-Si stretching vibration associated with the incorporation of titanium species into silica lattice [4], This indicates that the amorphous wall of Ti-MCM-41 was transformed into the TS-1 structure. 

The catalytic activitira of synfliesized catalysts are given in Table 1. The TS-1 catalyst exhibited the highest epoxide yield and the best catalytic performance for the epoxidation of 1-hexene. The convasion of cyclohexene, however, is the lowest over TS-1. In case of TS-1/MCM-41-A and TS-1/MCM-41-B, the selectivity to epoxide is much hi er than that of Ti-MCM-41. Moreover, the conversion of 1-hexene as well as cyclohexene is found larger on the TS-l/MCM-41-Aand TS-1/MCM-41-B than on other catalysts. While the epoxide yield from 1-hexene is nearly equivalent to that of TS-1, the yield from cyclohexene is much larger than those of the otiier two catalysts. Th e results of olefins epoxidation demonstrate that the TS-l/MCM-41-Aand TS-1/MCM-41-B possess the surface properties of TS-1 and mesoporosity of a typical mesoporous material, which were evidently brou in by the DGC process. 

Titanium containing hexagonal mesoporous materials were synthesized by the modified hydrothermal synthesis method. The synthesized Ti-MCM-41 has hi y ordered hexa rud structure. Ti-MCM-41 was transformed into TS-l/MCM-41 by using the dry gel conversion process. For the synthesis of Ti-MCM-41 with TS-1(TS-1/MCM-41) structure TPAOH was used as the template. The synthesized TS-l/MCM-41 has hexagonal mesopores when the DGC process was carried out for less than 3 6 h. The catalytic activity of synthesized TS-l/MCM-41 catalysts was measured by the epoxidation of 1-hexene and cyclohexene. For the comparison of the catalytic activity, TS-1 and Ti-MCM-41 samples were also applied to the epoxidation reaction under the same reaction conditions. Both the conversion of olefins and selectivity to epoxide over TS-l/MCM-41 are found hi er flian those of other catalysts. 

The Ti was loaded using two methods direct incorporation into the synthesis mixture, and post-synthesis grafting. In all cases the Ti-loading was 1.5 -1.8 wt%. Selectivity towards the epoxide was always 100%. Table 41.1 summarizes the results comparing Ti-TUD-1 and Ti-MCM-41 for cyclohexene epoxidation (15). For the direct incorporation, Ti-TUD-1 is five times more active than Ti-MCM-41, even though they have equivalent surface area. However, the grafted MCM-41 is also more active than its as-synthesized counterpart. 

Not only has the Ti precursor been investigated, but also the structure of the molecular sieve has been heavily investigated. Thus we now have an array of silica and silica-alumina molecular sieve supported Ti catalysts. These include Ti on amorphous Si02,10,11 Ti on a variety of Si02 mixed oxides,12 Ti-0 (titanium-beta),13"17 Ti-MCM-48,18 Ti-MCM-41,19 Ti-HMS,18 titanium-... 

Mn impregnated into MCM-4i, a silicalite containing uniform mesopores of approximately 22 A, catalyzes TBHP epoxidation of alkenes.88 Over Mn-MCM-41, both cis- and trans-stilbene yield trans-stilbene oxide, which the authors conclude signals a radical mechanism.88 In contrast, over Ti—MCM-41, trans-stilbene cannot be oxidized, only cis-stilbene is epoxidized to the cis-stilbene oxide, which suggest a radical-free mechanism.89 Finally, emphasizing the shape selectivity possibilities, only trans-stilbene (not cis-stilbene) can be epoxidized over Mn-ZSM-5, a zeolite with relatively small pores of 5.1 x 5.4 A (Fig. 6.14).88... 

Carotenoids incorporated in metal-substituted MCM-41 represent systems that contain a rapidly relaxing metal ion and a slowly relaxing organic radical. For distance determination, the effect of a rapidly relaxing framework Ti3+ ion on spin-lattice relaxation time,and phase memory time, Tu, of a slowly relaxing carotenoid radical was measured as a function of temperature in both siliceous and Ti-substituted MCM-41. It was found that the TM and 7) are shorter for carotenoids embedded in Ti-MCM-41 than those in siliceous MCM-41. 

For the Ti(OiPr)4/silica system, the advantage of MCM-41 (a mesoporous silica) over an amorphous silica is not evident either in terms of activity or selectivity for the epoxidation of cyclohexene with H202 in tert-butyl-alcohol.148 Nevertheless, deactivation of the catalysts seems slower, although the selectivity of the recovered catalysts is also lower (allylic oxidation epoxidation = 1 1). Treatment of these solids with tartaric acid improves the properties of the Ti/silica system, but not of the Ti/MCM-41 system, although NMR,149 EXAFS,150 and IR151 data suggest that the same titanium species are present on both supports. 

The catalyst samples were prepared in our laboratory. The synthesized Na-ZSM-5 zeolite was modified by conventional or solid state ion-exchange [11] to form H-, Fe-, Cu-, Ni- and Ti-ZSM5 samples, while the mesoporous catalysts (Fe- and Ti-MCM-41) were synthesized by isomorphous substitution [12], as well as the hydrotalcites containing Fe-, Cu-, Cr- or Ca-oxide in the Mg,Al-LDH structure [13]. 

Khenkin, A.M. and Neumann, R. (2000). Aerobic photochemical oxidation in meso-porous Ti-MCM-41 epoxidation of alkenes and oxidation of sulfides. Catal. Lett. 68(1-2), 109-111... 

Ti-MCM-41 and Ti-MCM-48 titanium-containing Mobil composite materials/mesopor-... 

Why is TS-1 more chemoselective than Ti-beta and Ti-MCM-41 (17—19) even though Ti4+ ions are isolated and in near-tetrahedral locations in all of them Are differences in hydrophobicity/hydrophilicity between TS-1 and the large/mesoporous material the only factors responsible for the lower... 

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