Applied Catalysis A: General, Vol.264, No.2, 133-139, 2004
Effect of steaming on one-step oxidation of benzene to phenol with nitrous oxide over Fe/MFI catalysts
One-step oxidation of benzene with N2O to phenol was studied over the iron-zeolite catalysts Fe/MFI and HMFI containing an Fe impurity. Catalysts were probed at 723 K and near atmospheric pressure using a fixed bed micro-flow reactor and a molar feed ratio of benzene/N2O/He = 1/3/36. A plot of the activity as a function of the loading with accessible iron, shows that mono-nuclear sites, are much more active for this reaction than dinuclear sites, which are known to catalyze NOx reduction. The benzene to phenol reaction is found to be of the consecutive type, all CO2 is formed by burning of phenol. The reaction order at these conditions is zero both in benzene and N2O. A steam pretreatment at 923 K of the low Fe-containing catalyst is found to be instrumental in the formation of the "Ex-lattice" Fe sites, required for the reaction. The same treatment when applied to high Fe-load catalysts leads also to growth of Fe oxide particles, and likely favors formation of a solid solution of Fe and Al oxide. The catalyst is deactivated by coke deposits. This can be largely suppressed by water vapor in the feed, resulting in a stable performance. It is assumed that H2O displaces C6H5OH from the sites. (C) 2004 Elsevier B.V. All rights reserved.
Keywords:benzene oxidation with N2O to phenol;Fe/MFI;Fe/ZSM-5;catalyst deactivation;steaming;consecutive reaction