Synthesis of transition metal-titanosilicate catalysts for benzene hydroxylation

Abstract

The microporous (TS-1 and Ti-MWW) and mesoporous (Ti-MCA and Ti-SBA-15) titanosilicates with the transition metal were successfully synthesized by hydrothermal followed by impregnation method. The transition metals in this study were Ce, Cu, Fe, and V. All synthesized products were characterized the physical properties by using X-ray powder diffraction, N2 adsorption-desorption, DR-UV spectrophotometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and inductively coupled plasma mass spectrometry (ICP-MS). After the bimetallic catalysts modification, the porous materials still preserved structure of parent materials. Moreover, the second metal was dispersed on the surface of titanosilicate supporter which confirmed by TEM results. The catalytic activity of the prepared catalysts was evaluated in the benzene hydroxylation with hydrogen peroxide as the oxidizing agent. Among various kind of second metals, V presented the best catalytic activity in all titanosilicate supports. The presence of V in catalyst remarkably enhanced catalytic oxidation capacity because of the increase of active site. Nature and dispersion of vanadium species as well as structure of titanosilicate support had tremendous effect on the yield of phenol product. At the optimum reaction condition of each catalyst, vanadium supported on Ti-MWW with 5 wt.% V-content showed highest catalytic performance with 14.72% yield of phenol. The three-dimensional and unique pore system of Ti-MWW made the efficient diffusion and transport of reactants resulting in high catalytic performance. The optimum condition in benzene hydroxylation was carried at benzene: H2O2 mole ratio of 1:3, 0.1 g of 5 wt.% V/Ti-MWW, acetonitrile 5.66 g, 55˚C for 3 h.