An isotope labelling study of the deactivation of a Pt/alumina catalyst used for propane dehydrogenation.

Abstract

This chapter investigates the form and reactivity of the carbonaceous deposit using 13 C and 2 H transient isotopic labeling techniques in a study of propane dehydrogenation. The activity and selectivity of the Pt/alumina catalyst for propane dehydrogenation is critically dependent on the extent of formation of a carbonaceous deposit, which contains both carbon and hydrogen, on the catalyst. Within the carbonaceous deposit, there is mixing of both the carbon and the hydrogen as revealed by isotopic tracer studies. Deactivation of the catalyst has been followed and the amounts of carbon deposited determined. Only a relatively small fraction of the carbon laydown on the surface can be removed by high temperature dioxygen treatment. After regeneration, carbon continues to build up on the catalyst surface in subsequent propane dehydrogenation reactions. Pretreatment of the catalyst with carbon monoxide or toluene at the reaction temperature results in carbon laydown on the catalyst, which dramatically reduces the amount of carbon deposition and increases the selectivity in subsequent propane dehydrogenation reactions. However, the carbon deposited during the pretreatment is different from that formed during propane dehydrogenation. Regeneration of the catalysts has also been examined and the efficiency of the regeneration method and its effect on the catalyst established. The effects of pre-poisoning of the catalyst, using either carbon monoxide or toluene as a specific carbon species, on the deactivation and selectivity of the catalyst for propene formation has also been investigated.