Effect of the pretreatment temperature on the catalytic activity of ZSM-5 zeolites

Abstract

The catalytic activities of ZSM-5 zeolite for the conversions of propane, pentane, hexane, and heptane and the isomerization of o-xylene were examined as a function of the temperature of the pretreatment of the zeolite. An activity maximum was observed at the pretreatment temperature of 580 °C for the conversion of propane. For the other four reactions, the double maxima were observed around 400 ° and 580 °C, indicating the presence of two types of active centers. It is suggested that the acidic centers that give a maximum at 580 °C are hydroxyl groups interacting with aluminium species dislodged from the framework. The specific activity of these centers are estimated to be much higher than that of the conventional hydroxyl groups for hydrocarbon reactions. The participation of dislodged aluminium species for producing stronger acid centers is supported by the enhancing effect of the steaming on the catalytic activity for propane conversion.