Abstract
The ZSM-5 zeolites with Si/Al ratio 50 and 80 (ZSM-5-50 и ZSM-5-80) modified by Ca-, Sr-, Cr-, Mn- и Sb-ions were synthesized and investigated in oxidation of benzene to phenol. It was shown that more active and selective in direct oxidation of benzene by nitrous oxide are catalysts containing about 0.1–0.2% of Sb. It formally corresponds to substitution of 1/12 and 1/6 ions of H-ions by Sb-ions in ratio 1 : 1 of zeolite. Yield of phenol equal to 61.2% was obtained at 450°C and contact time 1 sec. with selectivity to phenol 96% in the presence of (ZSM-5-50 + 1/12 Sb) sample. It is about twice as much than an average value of yield reported in literature for other Me-ZSM-5 catalysts. Also, (ZSM-5-50 + 1/6 Sb) sample revealed much higher stability than other catalysts based on ZSM-5 zeolites. A model of nitrous oxide activation over single active sites (located very distant from each other) of the catalyst is suggested. The suggested model of single site adsorption and catalysis allows explain more higher efficiency of nitrous oxide as oxidant than that of molecular oxygen in reaction of direct oxidation of benzene to phenol, especially over catalysts with a low concentration (less than 0.1%) of |Me-ions.
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