Effect of high-temperature treatment on Fe/ZSM-5 prepared by chemical vapor deposition of FeCl 3: II. Nitrous oxide decomposition, selective oxidation of benzene to phenol, and selective reduction of nitric oxide by isobutane

Abstract

The catalytic performance (nitrous oxide decomposition, hydroxylation of benzene to phenol with nitrous oxide, and selective reduction of nitric oxide by i-butane) was evaluated for a set of HZSM-5 and sublimed Fe/ZSM-5 catalysts, which have been extensively characterized in an earlier contribution (J. Catal. (2003)). Nitrous oxide decomposition rates for the sublimed samples strongly increase after high-temperature calcination and particularly, after high-temperature steaming. Only a small fraction of the total iron content is active in this decomposition. For benzene hydroxylation the initial phenol productivity also increases with increasing severity of treatment. It is concluded that similar catalytic sites are important. Nevertheless, Fe/ZSM-5 and Fe/ZSM-5(HTC) exhibit relatively low phenol selectivities due to significant hydrocarbon combustion. The steamed Fe/ZSM-5, however, produces phenol with high selectivity. The stability of the sublimed samples is relatively low due to the large coke make, attributable to the large number of active sites. Commercial HZSM-5 with an iron content of 0.024 wt% and its steamed counterpart are also active and have a better stability, the latter one having the highest phenol productivity after prolonged reaction times. The beneficial effect of severe activation treatments to sublimed Fe/ZSM-5, where iron is introduced at extraframework positions, is taken as an indication that removal of lattice aluminum is important for the generation of active sites. The different activity order in NO reduction by i-butane suggests that the active sites for this reaction are different from those for nitrous oxide decomposition and selective benzene oxidation.