Catalytic Properties of Ti-HMS with High Titanium Loadings

Abstract

Ti-HMS samples in which titanium species exist in various forms of isolated tetrahedral state, finely dispersed <TEX>$TiO_2$</TEX> cluster, and some in extra-framework anatase phase were prepared via a direct synthesis route using dodecylamine (DDS) as a structure directing agent by systematically varying the titanium loadings between 2 and 50 mol% Ti/(Ti+Si) in substrate composition. Physicochemical properties of the materials were evaluated using XRD, SEM/TEM, N2 adsorption, UV-vis and XANES spectroscopies. Catalytic properties of Ti-HMS in cyclohexene and 2,6-di-tert-butyl phenol (2,6-DTBP) oxidation using aqueous <TEX>$H_2O_2$</TEX>, and vapor phase photocatalytic degradation of acetaldehyde were evaluated. High <TEX>$H_2O_2$</TEX> selectivity was obtained in cyclohexene oxidation, and cyclohexene conversion was found primarily dependent on the amount of tetrahedrally coordinated Ti sites. For bulky 2,6-DTBP oxidation and photocatalytic oxidation of acetaldehyde, on the other hand, conversions were found dependent on the total amount of Ti sites and maintaining an uniform mesoporous structure in the catalysts was not critical for efficient catalysis.