Ti-containing mesoporous catalysts with MCM-41 structure have been successfully prepared by direct hydrothermal synthesis These mesoporous materials were compared with pure siliceous MCM-41 synthesized at the same conditions An extended and detailed study, which includes the effects of several factors such as the state and content of Ti, surfactant/Si ratio and template removal technique on the physicochemical properties and catalytic activity of Ti-MCM-41, is presented in this contribution Various techniques including XRD, FT-IR, DRUV–vis, ICP and N2 adsorption were employed for the materials characterization An optimum surfactant/Si molar ratio in the synthesis gel for the highest regularity of the formed mesostructure was found Both the structure stability and the local environment of Ti sites in mesostructures with different degrees of Ti loading (010–322 wt%) have been carefully investigated Based on a combined FT-IR and DRUV–vis study and ICP analysis, it was possible to conclude that Infrared spectroscopy can result a powerful tool to verify the Ti(IV) incorporation into the framework of MCM-41 Therefore, a simple and novel method for estimation of framework Ti content could be developed Also, these materials were catalytically tested in the oxidation of cyclohexene with aqueous hydrogen peroxide Finally, the catalysts could be regenerated without any loss in activity/selectivity

Synthesis, characterization and selective oxidation properties of Ti-containing mesoporous catalysts

a b s t r a c t Al-containing mesoporous catalysts with MCM-41 structure and high surface area have been success- fully prepared by direct hydrothermal synthesis. Various characterization techniques including XRD, N2 adsorption, ICP-OES, NMR, FT-IR and adsorption of pyridine coupled to FT-IR spectroscopy were employed. A detailed study about the relationships existing between the different synthesis parame- ters, the physico-chemical properties, the acid behavior and the catalytic performance is presented in this contribution. We have suggested that the active sites for the Beckmann rearrangement of cyclo- hexanone oxime are nest silanols (at structural defects) of very weak Bronsted acid character, which is associated with the introduction of Al into the mesoporous framework. In all the cases, employing soft reaction conditions, we have obtained selectivity to caprolactam of 100%. Finally, a Si/Al initial molar ratio of 20, a stirring of synthesis gel for 7 h and a hydrothermal treatment of 6 days seem to be the optimum synthesis conditions to obtain the highest framework Al incorporation, more abundant weak acid sites (silanol nests) and maximum yield for -caprolactam.

Influence of the synthesis conditions on the physicochemical properties and acidity of Al-MCM-41 as catalysts for the cyclohexanone oxime rearrangement

Kuo-Tseng Li

Papers

Propylene epoxidation over Ti/MCM-41 catalysts prepared by chemical vapor deposition

Hydrogen sulfide oxidation on RE(RE = Sm, Y, La)–V–Sb catalysts: Effects of RE size and electronegativity