Ti-MCM-41 supported phosphotungstic acid: An effective and environmentally benign catalyst for epoxidation of styrene

Abstract

Mesoporous Ti-MCM-41 molecular sieve was synthesized under hydrothermal conditions. 5, 10, 20, 30 and 50 wt.% phosphotungstic acid (H 3PW 12O 40) (PW) were supported on Ti-MCM-41 and the resulting catalysts were characterized by powder X-ray diffraction (XRD), N 2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). The host material suffers severe structural distortions at higher loading, which lead to a considerable loss of long-range orders. Their catalytic performances were evaluated in the epoxidation of styrene with dilute H 2O 2 (30%) as an oxidizing agent under liquid-phase reaction conditions over PW/Ti-MCM-41 catalysts for selective synthesis of styrene oxide. The influences of various reaction parameters such as temperature, time, solvents, PW loading and catalyst amount, styrene to H 2O 2 mmol ratios and acetonitrile (MeCN) to N, N-dimethylformamide (DMF) volume ratios on the conversion of styrene and yield as well as selectivity of styrene oxide have also been studied in details. The results revealed that 20% PW/Ti-MCM-41 was more active than other catalysts. The PW/Ti-MCM-41, moreover, was found to be reusable and effective for the epoxidation of styrene.