Characteristics of Ti-MCM-41 and its Catalytic Properties in Oxidation of Benzene

Abstract

A series of mesoporous titanosilicate Ti-MCM-41 molecular sieves with various Si/Ti ratios have been hydrothermally synthesized using hexadecyl-trimethylammonium bromide as the organic surfactant. These materials were characterized with powder X-ray diffraction (XRD), framework FTIR, diffuse reflectance UV-visible spectroscopy, nitrogen sorption measurements, differential thermal analysis (DTA), and transmission electron microscopy (TEM). The crystallinity of Ti-MCM-41 after calcination was almost two-fold higher than that of the as-synthesized one. The crystallinity and surface area of Ti-MCM-41 both decrease with an increase of titanium content. The results of XRD and FTIR show that the solid products have the MCM-41 structure and contained only atomically dispersed titanium, consistent with framework titanium in Ti-MCM-41. All of the materials had a uniform pore size distribution with pore size of around 3.0 nm. The hexagonal array structure of uniform pore size was observed by TEM. It proved that the pores were highly aligned. The catalytic activities of Ti-MCM-41 were tested in the partial oxidation of benzene by diluted hydrogen peroxide in a batch reactor. Ti-MCM-41 had a higher activity than TiO2 and Ti/NaY. The activity of Ti-MCM-41 increased with titanium content. The activity of Ti-MCM-41 prepared with hydrothermal synthesis was higher than that of the sample prepared with impregnation. The high activity in Ti-MCM-41 can be attributed to its hydrohobicity and large pore size. Phenol was the only liquid phase product on all of the samples.