Effect of lanthanum addition on the properties of potassium-free catalysts for ethylbenzene dehydrogenation

Abstract

The ethylbenzene dehydrogenation in the presence of steam is the dominant technology for styrene production, one of the most important high value chemicals. The most widely used industrial catalyst comprises potassium-promoted iron oxide, which deactivates with time, due to potassium loss. In order to find alternative free-potassium catalysts, the effect of lanthanum on hematite-based catalysts was studied in this work. Samples with different amounts of lanthanum and prepared with different precipitants (ammonium hydroxide, sodium carbonate and sodium hydroxide) were obtained. It was found that lanthanum led to the production of solids with small particles when ammonium hydroxide was used, a fact which was assigned to lanthanum species on the surface where they keep the hematite particles apart avoiding sinterization. On the other hand, bigger particles were produced when sodium hydroxide and sodium carbonate are used, which resulted in solids with small specific surface areas. This was related to the sodium species which covered the surface impairing the lanthanum action. The most promising catalyst was that prepared with ammonium hydroxide and with La/Fe = 0.1, which showed the highest specific activity and the highest activity per area. In this solid, lanthanum acts as a structural promoter.