Nonoxidative and oxidative dehydrogenation of ethylbenzene over Zn [sbnd]Fe [sbnd]Cr ternary spinel system

Abstract

The nonoxidative dehydrogenation of ethylbenzene (EB) over Zn(Fe x Cr 2− x )O 4 ( x = 0 (ZC1), x = 0.5 (ZCF2), x = 1.0 (ZCF3), x = 1.5 (ZCF4) and x = 2.0 (ZF5)) series was carried out in the temperature range 490–580°C. The overall conversion of ethylbenzene increases with temperature while the formation of styrene and its selectivity follows the following order ZC1 < ZCF2 < ZCF3 > ZCF4 > ZF5. By comparing the acidity and basicity data with the results of catalytic transformations of ethylbenzene it is concluded that both basic and acidic sites are responsible for the catalytic activity which are in optimum level over ZCF3 ( x = 1). The effect of contact time and the influence of products on the conversion of ethylbenzene indicates that desorption of styrene over ZCF3, ZCF4 and ZF5 and adsorption of ethylbenzene over ZC1 and ZCF2 are the rate determining steps. It is also observed that the passage of styrene along with ethylbenzene does not affect the yield of benzene but increases that of toluene indicating that benzene is formed by parallel reaction, while toluene is formed by parallel and consecutive reactions. Oxidative dehydrogenation of ethylbenzene was done by passing 10 ml of air/min along with ethylbenzene in the temperature range 300–450°C. The overall conversion of ethylbenzene and the formation of styrene and CO 2 are increased with increase in temperature over all catalysts. The relatively higher conversion of ethylbenzene and yield of styrene over ZCF3, lower conversion and yield of styrene over ZCF4 and ZF5 are due to the presence of stable Fe 3+/Fe 2+ redox couple in the former and reduction of Fe 3+ to Fe 0 in the latter.