Kinetics of benzene to phenol oxidation over Fe-ZSM-5 catalyst

Benzene to phenol oxidation by nitrous oxide over the Fe-ZSM-5 catalyst was studied at 648-698 K and near atmospheric pressure using a bench scale plug flow reactor with a feed gas concentration of 30-80 mol% benzene, 1.5-5.0 mol% N2O, and 0-4.7 mol% phenol. At these conditions, the selectivity of benzene and N2O to phenol exceeded 98 and 95%, respectively. Benzoquinone, hydroquinone, catechol, and carbon oxides were the main by-products. The rate of N2O consumption was observed to be first order with respect to N2O concentration, and was observed to decrease with increasing benzene and phenol concentration. The apparent activation energy was 126 kJ/mol. A sorption kinetic model was developed. It was assumed that benzene and phenol are in sorption equilibrium between the gas-phase and the zeolite micropore volume. The limiting step of the overall reaction sequence is the reaction between sorbed N2O and catalyst active sites bound with phenol. The interaction of sorbed benzene and phenol with oxidized alpha-sites is relatively fast. The equilibrium constant for benzene sorption on ZSM-5 was estimated from the kinetic data and was found to be in a good agreement with the sorption measurements reported in the literature. It was observed that the ratio of the specific rate of phenol formation to the specific rate of dihydroxybenzene formation is independent of temperature. (C) 2003 Elsevier Science B.V. All rights reserved.