Oxidative dehydrogenation of ethylbenzene on activated carbon catalysts 3.Catalyst deactivation

Extended catalytic tests show that coke deposition is responsible for the d eactivation of activated carbon catalysts in the oxidative dehydrogenation of ethylbenzene (ODE). Temperature-programmed desorption (TPD), DRIFTS, tex tural and elemental analyses of used catalysts have shown that not only the great majority of the micropores become blocked, but also that the amounts of oxygen and hydrogen in the catalyst composition increase with time on s tream, leading to a material increasingly more reactive towards oxidation. It was observed that after a few days on stream, the rate of carbon gasific ation became larger than the rate of coke deposition, leading to a decrease in catalyst weight. Working under milder conditions (lower temperature and oxygen partial press ure) delayed this effect. The increase in the concentration of surface grou ps with time does not result in a proportional increase in the activity of the catalysts, because the majority of the groups created are not active fo r the ODE reaction. (C) 2001 Elsevier Science B.V. All rights reserved.