The oxygen effect in the conversion of C2H6, C3H8, and n-butane to aroms. using two H-ZSM-5 zeolites with different Si/Al ratios is studied. The presence of small amts. of gas-phase O increases C6H6-PhMe-xylene formation, in particular at the lower reaction temps. (<773 K). The enhancement factor compared to anaerobic activity is higher for the less reactive alkane (C2H6) and for the less active zeolite (Si/Al = 164) which also shows the lower total oxidn. activity. The formation of C oxides decreases considerably when the surface acidity is inhibited by K exchange, and the K zeolite is active only in the oxidative dehydrogenation of the alkane. However, the aerobic activity of the zeolite is also correlated to surface acidity. It is suggested that the main O effect is in the first stage of alkane activation, enhancing the formation of the corresponding olefin. The creation of new active sites is attributed to the interaction of O with solid-state defects forming very reactive O free radical species. Their activity, however, is inhibited during reaction due to the formation of carbonaceous residues. [on SciFinder(R)]
Effect of oxygen on the conversion of light paraffins on ZSM-5 zeolites
CENTI, Gabriele;
1989-01-01
Abstract
The oxygen effect in the conversion of C2H6, C3H8, and n-butane to aroms. using two H-ZSM-5 zeolites with different Si/Al ratios is studied. The presence of small amts. of gas-phase O increases C6H6-PhMe-xylene formation, in particular at the lower reaction temps. (<773 K). The enhancement factor compared to anaerobic activity is higher for the less reactive alkane (C2H6) and for the less active zeolite (Si/Al = 164) which also shows the lower total oxidn. activity. The formation of C oxides decreases considerably when the surface acidity is inhibited by K exchange, and the K zeolite is active only in the oxidative dehydrogenation of the alkane. However, the aerobic activity of the zeolite is also correlated to surface acidity. It is suggested that the main O effect is in the first stage of alkane activation, enhancing the formation of the corresponding olefin. The creation of new active sites is attributed to the interaction of O with solid-state defects forming very reactive O free radical species. Their activity, however, is inhibited during reaction due to the formation of carbonaceous residues. [on SciFinder(R)]Pubblicazioni consigliate
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