Characterization of platinum–iron catalysts supported on MCM-41 synthesized with rice husk silica and their performance for phenol hydroxylation

摘要

Mesoporous material RH-MCM-41 was synthesized with rice husk silica by a hydrothermal method. It was used as a support for bimetallic platinum?iron catalysts Pt–Fe / RH-MCM-41 for phenol hydroxylation. The catalysts were prepared by co-impregnation with Pt and Fe at amounts of 0.5 and 5.0?wt.% , respectively. The RH-MCM-41 structure in the catalysts was studied with x-ray diffraction, and their surface areas were determined by nitrogen adsorption. The oxidation number of Fe supported on RH-MCM-41 was + 3 , as determined by x-ray absorption near edge structure (XANES) analysis. Transmission electron microscopy (TEM) images of all the catalysts displayed well-ordered structures, and metal nanoparticles were observed in some catalysts. All the catalysts were active for phenol hydroxylation using H₂O₂ as the oxidant at phenol?: H₂O₂ mole ratios of 2?:?1, 2?:?2, 2?:?3 and 2?:?4. The first three ratios produced only catechol and hydroquinone, whereas the 2?:?4 ratio also produced benzoquinone. The 2?:?3 ratio gave the highest phenol conversion of 47% at 70?°C . The catalyst prepared by co-impregnation with Pt and Fe was more active than that prepared using a physical mixture of Pt / RH-MCM-41 and Fe / RH-MCM-41.