Steam-assisted crystallized Fe-ZSM-5 materials and their unprecedented activity in benzene hydroxylation to phenol using hydrogen peroxide

Abstract

Iron-containing, hierarchical steam-assisted crystallized MFI materials were found to possess unprecedented reactivity for benzene hydroxylation to phenol. Numerous characterization methods were used to confirm the crystallinity, composition, textural properties and iron coordination in these samples. In-situ Fourier-transform infrared spectroscopy (in-situ FT-IR) of methanol and nitric oxide adsorption were also used to probe the materials. These catalysts were then studied in the catalytic oxidation of benzene to phenol using hydrogen peroxide as oxidant at mild conditions. Microporous materials showed lower activity (∼4% phenol yield after 8 h), in agreement with previous reports, whereas hierarchical Fe-ZSM-5 zeolites, as synthesized here, exhibited superior catalytic performance. The best catalyst in this report gave a benzene conversion of 25.5% with a phenol selectivity of 90% corresponding to a turnover number of 82. This finding is twice the best zeolite-based catalyst in the open literature. Suitable control experiments ruled out homogeneous catalysis. Hydrogen peroxide consumption was also higher for the hierarchical samples, up to 95% at eight hours, compared to conventional catalysts. The obtained results revealed that the active sites for this reaction were located predominantly in the micropores of the mesoporous Fe-ZSM-5 zeolites.