Hydroxylation of benzene on ZSM5 type catalysts

Abstract

Publisher Summary With a zeolite socony mobil-5 (ZSM5) type zeolite in its acid form as catalyst and nitrous oxide as oxidant, benzene may be directly oxidized to phenol. ZSM5 type zeolites were used as catalysts for the one-step synthesis of phenol by benzene partial oxidation with nitrous oxide. It is generally agreed upon that ZSM5 type catalysts are outstanding among a wide range of metal oxide and zeolite catalysts in this gasphase-reaction. Besides H-Al-ZSM5, especially H-Fe-ZSM5 and H-Al/Fe-ZSM5 zeolites, were used as catalysts. While the suggested mechanisms are quite different, similar experimental results were obtained concerning the dependence on temperature and partial pressures of the reactants. Furthermore, appreciable coke formation led to a loss in catalyst activity in all cases. All zeolite samples were synthesized by the hydrothermal method described in detail. The experiments were performed in a completely automated laboratory setup, including an integrally operated plug flow tubular reactor. Reaction components were analyzed by online gas chromatography with flame ionization detector (FID) and thermal conductivity detector (TCD). It is found that except phenol only benzoquinone was produced in higher yields. Formation of CO2 was not observed below 400°C. Initial phenol yields were about 25%, but deactivation by coke formation quickly led to a decreasing activity.