On the role of Bronsted acidity in the oxidation of benzene to phenol by nitrous oxide

Oxidation of benzene to phenol with nitrous oxide being an untypical reaction for zeolite catalysis arouses a great interest among researchers. Several hypotheses concerning reaction mechanism are discussed. Some of them assume a key role of the Bronsted acid centers (BAC), though few experimental support for this idea is available. The goal of this work is to study the Bronsted acidity of FeZSM-5 zeolite catalyst (0.13 wt.% Fe2O3) to reveal a relationship (if any) between the BAC concentration and the catalytic activity in benzene oxidation. Various pretreatments of the sample including a high-temperature calcination up to 900 degrees C were used to vary the BAC concentration, which was measured by infrared spectrometry. No evidence of the Bronsted acidity importance for catalyzing the reaction was found. What is more, a formal inverse correlation was discovered. Thus, a manifold decrease in BAC concentration was accompanied by a remarkable increase in the oxidation rate, with a small acid recreation under the reaction conditions used. The obtained results support an earlier suggested redox mechanism of the reaction involving a special oxygen form produced at N2O decomposition on Fe-containing active sites.