Direct organic functionalization of Ti-MCM-41: Synthesis condition, organic content, and catalytic activity

The conditions for the direct synthesis of organically functionalized Ti-substituted MCM-41 materials have been investigated to improve the catalytic efficiency in epoxidation reactions. The 29Si MAS NMR measurements indicate that there is a strong correlation between the catalytic activity and the surface hydrophobicity estimated by means of water adsorption capacity regardless of the kind of modifying organic groups. In the oxidation of alkenes, the organically functionalized Ti-MCM-41 materials having high surface hydrophobicity exhibit high catalytic performance as well as low non-productive H2O2 decomposition rates, and the highest activity is obtained when the water adsorption capacity per surface area is ca. 1.0 molecule-H2O nm−2. Further organic functionalization leads to the decrease in the activity in spite of the increased surface hydrophobicity probably due to the inaccessibility of reactant molecules to the catalytically active centers surrounded by a large number of terminal organic groups. In addition, the organic functionalization of Ti-MCM-41 has proved to suppress the Ti-leaching during the oxidation reactions.