Oxidative Dehydrogenation of Alkylbenzenes over Supported Palladium Catalysts Modified by Halide Ions

Abstract

It was found that ethylbenzene was oxidatively dehydrogenated at about 200 to 300°C on supported palladium catalysts modified by halogen ions to give styrene in high selectivity. Since bromine ion was found to be most effective in modifying the activity and selectivity of the catalyst, sodium bromide was use in this experiment. The apparent activation energy was 7.8 kcal/mol and 16.1 kcal/mol for styrene formation and carbon dioxide formation, respectively. While the rate of styrene formation was proportional to the partial pressure of ethylbenzene, it was expressed by a Langmuir equation with respect to oxygen.
Other alkylbenzenes such as propyl- and butylbenzenes were also oxidatively dehydrogenated on the catalyst to form alkenylbenzenes in which double bond existed at the β-position to aromatic rings. The reactivity of each alkylbenzene decreased with the increase in the carbon number of the alkyl group. The alkylbenzene with straight chain exhibited high activation energy in the reaction and suppressed the formation of styrene when it was reacted competitively with ethylbenzene. This fact was explained on the basis of a possible assumption that the alkylbenzene with straight chain adsorbed on the catalyst in larger quantities than ethylbenzene.