characterization of MCM-41 from rice husk silica and utilization as supports for platinum-iron catalysts For Phenol hydroxylation

摘要

MCM-41 was prepared with rice husk silica by hydrothermal method and used as a support for bimetallic platinum -iron catalysts, denoted as Pt-Fe/MCM-41, which were prepared by co-impregnation with Pt and Fe amount of 0.5 and 5.0% by weight, respectively. The MCM-41 structures in all catalysts were confirmed by XRD and their surface areas, determined by nitrogen adsorption, were lower than that of the parent MCM-41. The oxidation number of iron supported on MCM-41, analyzed by XANES was +3. The TEM micrographs of all catalysts displayed well-order structure and nanocrystals of metal could be seen in some catalysts. All catalysts were active for phenol hydroxylation using H2O2 as an oxidant when the phenol:H2O2 ratios were varied at 2:1,2:2, 2:3 and 2:4. The first three ratios produced only catechol and hydroquinone whereas the 2:4 ratio produced another unknown product. The 2:3 ratio gave the highest conversion of 47% at 70°C.The catalyst prepared by co-impregnation from Pt and Fe precursors was more active than a physically mixture of Pt/MCM-41 and Fe/MCM-41.