MCM-41 modified heterogeneous catalysts from rice husk for selective oxidation of styrene into benzaldehyde

Abstract

This study examined the preparation of MCM-41, Ni-MCM-41 and Co-MCM-41 from silica extracted from rice husk ash (RHA) via sol–gel technique. The materials were characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FT-IR), Diffuse reflectance UV–Vis (DR/UV–Vis),Energy Dispersive X-ray Spectrometry (EDX), N 2 adsorption–desorption and NH 3 TPD. XRD and TEM analyses showed reduction in the long range order upon the introduction of heteroatoms into MCM-41 framework. Successful substitution of Si 4 + with metal cations was verified by the shifting in the siloxane (Si-O-Si) bond. Presence of nickel phyllosilicates was evidenced from the FT-IR and DR/UV–Vis investigations. Mesoporous behavior with capillary condensation was unchanged even after the incorporation of Ni and Co species into the MCM-41 matrix. MCM-41 and modified MCM-41 catalysts were evaluated in the liquid-phase oxidation of styrene for 4 h under the influence of reaction parameters such as reaction temperature, catalyst loading, types of solvent and molar ratio of styrene : H 2 O 2 . Under the optimum condition of 343 K, 0.20 g catalyst, 1:4 molar ratios and DMF as the reaction medium, the activity was found to increase following the trend: Ni-MCM-41 (79.9%) >Co-MCM-41(56.6%) > MCM-41 (40.7%). Benzaldehyde was the sole product over Ni-MCM-41 and Co-MCM-41 while MCM-41 gave benzaldehyde (96.0%) and styrene oxide (4.0%). Surface characteristics and TPD acidity strength was found to govern the catalysis. Negligible leaching (0.448 ppm) and exceptional activity during successive reruns demonstrates that Ni-MCM-41 was beyond doubt, heterogeneous in nature. This research signifies a successful conversion of waste biomass into value added products. • Cobalt and nickel supported MCM-41 catalysts were synthesized from rice husk. • The catalyst was active in the oxidation of styrene at mild condition. • Benzaldehyde was the sole product over the modified MCM-41 catalysts. • The catalysis of Ni-MCM-41 was heterogeneous in nature with minor leaching. • Successful conversion of waste biomass into benign product.