Integrated Mechanochemical/Microwave-Assisted Approach for the Synthesis of Biogenic Silica-Based Catalysts from Rice Husk Waste

A template-free, simple, effective, and reproducible integrated mechanochemical/microwave promoted methodology has been designed to derive porous silica materials from rice husk waste. Microwave-assisted acid dissolution effectively removed metal ions from rice husk in order to obtain a highly pure (>95%) amorphous mesoporous silica with a surface area of 352 m(2) g(-1). As-synthesized silica materials were used as supports to prepare iron oxide-containing nanocatalyst via mechanochemistry employing a dry milling step in which the pore structure of silica was retained in the final materials after iron incorporation. Synthesized materials were characterized using different techniques including N-2 physisorption, powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and diffuse reflectance Fourier-transform infrared spectroscopy. Materials featured excellent and versatile catalytic activities in microwave-assisted oxidation and acid-catalyzed reactions. Toluene alkylation was successfully promoted in quantitative product yields with complete selectivity to monoalkylated products. The iron-containing catalyst exhibited good conversion (up to 44%) at complete benzaldehyde selectivity in the liquid-phase oxidation of benzyl alcohol.