Oxidation of Benzene to Phenol By Nitrous Oxide on Me-ZSM-5-Zeolites with a Low Concentration of Active Sites: Role of Single Active Sites

Abstract

Catalysts based on high-silica zeolites with Si/Al ratios of 50 and 80 (ZSM-5-50 and ZSM-5-80) modified by Ca, Sr, Cr, Mn, and Sb ions are synthesized and studied in the reaction of the oxidation of benzene to phenol by nitrous oxide. It is shown that catalysts containing about 0.1–0.2 wt % of Sb ions are more active and selective in the reaction of the direct oxidation of benzene to phenol by nitrous oxide. It formally corresponds to the substitution of 1/12 and 1/6 ions of H ions by Sb ions in a ratio of 1 : 1 of the zeolite. In the presence of a sample composed of ZSM-5-50 + 1/12 Sb at a temperature of 450°C and a contact time of 1 s, a phenol yield of 61.2% is achieved with a selectivity of 96%, which is approximately twice as high as the values known in the literature for other for other Me-ZSM-5 catalysts. At the same time, the sample with the composition of ZSM-5-50 + 1/6Sb turns out to be more stable than the other catalysts based on ZSM-5 zeolites. A model is also proposed for the activation of nitrous oxide on single active sites (located at a sufficient distance from each other) of the catalyst, which explains the higher efficiency of nitrous oxide as oxidant than that of molecular oxygen in the reaction of the direct oxidation of benzene to phenol in the presence of Me-ZSM-5 catalysts with a low concentration (less than 0.1%) of Me ions.