Catalysis Today 154 (2010) 224–228 Contents lists available at ScienceDirect Catalysis Today journal homepage: www.elsevier.com/locate/cattod Irreversible deactivation of styrene catalyst due to potassium loss—Development of antidote via mechanism pinning Weronika Bieniasz ∗ , Michał Tr ˛ ebala, Zbigniew Sojka, Andrzej Kotarba ∗ Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Krakow, Poland article info Article history: Available online 24 April 2010 Keywords: Styrene catalyst Potassium ferrites K2Fe22O34 Potassium loss Stability Iron oxides Work function abstract Potassium loss processes involved in irreversible deactivation of the -ferrite component of the styrene catalyst were investigated by means of Species Resolved Thermal Alkali Desorption and work function measurements in the process temperature range. Two main mechanisms of the stabilization were devel- oped depending on the dopant location. It was found that incorporation of Cr promoter into the structure of -ferrite slows down potassium diffusion from the bulk towards the surface, whereas the additive segregated at the basal planes (such as CeO 2 ), favoring the cationic state of potassium, inhibits the prob- ability of potassium atoms to leave the K 2 Fe 22 O 34 surface via work function increase. From the obtained results it may be concluded that K loss can be effectively extinguished via appropriate doping of the less stable -ferrite active phase of the iron-oxide catalyst. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Ethylbenzene dehydrogenation is the major catalytic dehy- drogenation process carried out in petrochemical industry. The worldwide annual production of styrene monomer exceeds 2 × 10 7 ton and makes it after ethylene, vinyl chloride and propylene one of the most used monomers [1]. The most widespread production route of styrene is the catalytic ethylben- zene dehydrogenation. The commercial process is carried out in adiabatic or isothermal mode in fixed bed reactor with radial or axial flow of the reactants. The process is highly endothermic (H 873K = 124.9 kJmol -1 ) and is accompanied with an increase in moles of the reactants. Most styrene production units are oper- ated under atmospheric or reduced pressure in temperature range of 550–650 ◦ C and the typical water-to-ethylbenzene ratio of 12:1 depending slightly on the catalyst and process used [2]. The commercial catalyst for the most styrene plants is based on iron oxide promoted with potassium with small amount of several additives—usually Al [3], Ce [4,5], Cr [6], Mg [7], Mn [8], Mo [9], Ti [10], and Zn [11]. Whereas, potassium acts as a chemical promoter increasing the catalyst activity by an order of magnitude, the other additives are textural and surface modifiers, stabilizing the high specific surface area of the catalyst. ∗ Corresponding authors. Tel.: +48 12 663 20 17; fax: +48 12 634 05 15. E-mail addresses: rozek@chemia.uj.edu.pl (W. Bieniasz), kotarba@chemia.uj.edu.pl (A. Kotarba). The main reasons for the iron-oxide catalyst deactivation in severe industrial conditions include formation of carbonaceous deposit, and loss of potassium promoter. While the first factor is reversible, and coke removal is achieved by steam co-feeding, the second factor is irreversible, and leads to the activity decay during the time on stream operation. Thus the comprehensive research has been dedicated to potassium loss processes from the model and real iron-oxide catalysts [12,13]. The interaction of potassium with iron-oxide matrix leads to a multicomponent, multiphase system with the following phases reported in open literature and patents: - and -Fe 2 O 3 , Fe 3 O 4 , KOH, K 2 CO 3 , KFeO 2 and K 2 Fe 22 O 34 [5,14]. The iron-oxide catalyst precursor corresponds to K-doped hematite. In the course of the solid-state restructuring two ferrite phases, KFeO 2 and K 2 Fe 22 O 34 , are formed and the active state of the catalyst surface is assigned to the equilibrium between them. The potassium thermal desorption studies revealed that the K 2 Fe 22 O 34 -ferrite, due to its specific layered -alumina structure is principally responsible for potas- sium volatilization from the styrene catalyst [15]. Additionally, it was shown that introduction of alien metal ions can substantially improve the stability of K 2 Fe 22 O 34 , whereas in the case of KFeO 2 the reverse effect of pronounced potassium thermal destabilization was observed [16]. Although potassium ferrites make the real iron-oxide cata- lyst active and selective, the severe process conditions accelerate its steady deterioration due to potassium loss and redistribution, requiring regular replacement of the catalyst in the installation every 1–2 years. A concise review of these problems can be found elsewhere [12]. Consequently, the investigations of potassium loss mechanism, as well as understanding of the influence of the addi- 0920-5861/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2010.03.059