Dehydrogenation of ethylbenzene over Fe–Ce–Rb and Fe–Ce–Cs mixed oxide catalysts

• Published in: Reaction kinetics, mechanisms and catalysis Vol. 109; no. 1; pp. 29 - 41
• Main Authors: Kano, Yusuke, Ohshima, Masa–aki, Kurokawa, Hideki, Miura, Hiroshi
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.06.2013
• Subjects: Catalysis; Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Physical Chemistry; Langmuir–Hinshelwood mechanism; Iron oxide; Rubidium addition; Ethylbenzene dehydrogenation; Cesium addition; Rate equation
• ISSN: 1878-5190; 1878-5204
• DOI: 10.1007/s11144-013-0549-2

Fe–Ce mixed oxide catalysts promoted by Rb and Cs have been investigated for the dehydrogenation of ethylbenzene. Fe–Ce–Rb and Fe–Ce–Cs were found to be highly active. X-ray diffraction (XRD) analysis confirmed the formation of RbFeO 2 and CsFeO 2 in the catalyst. X-ray photoelectron spectroscopy (XPS) analysis suggests a surface composition of the catalysts with an atomic ratio of Rb/Fe = 1, Cs/Fe = 1 and O/Fe = 2, meaning the surface is composed of the binary oxides, RbFeO 2 and CsFeO 2 . We conclude that the active phases of these catalysts are RbFeO 2 and CsFeO 2 , similar to KFeO 2 in the case of K–Fe and Fe–Ce–K mixed oxide catalysts. The rate equation of the reaction was determined supposing a Langmuir–Hinshelwood mechanism, in which the competitive adsorption of ethylbenzene and styrene dominate the reaction rate. However, the relative adsorption constant of styrene, Z ST , did not change significantly with the addition of Rb or Cs. The rate constant k increased with the addition of Rb or Cs. The activation energy increased with the addition of Rb or Cs compared with Fe–Ce, and the frequency factor also increased remarkably. Because the strong base points are most likely the active sites, addition of Rb and Cs increased the number of basic sites on the catalyst surface, resulting in higher activity. The kinetic factors, k and Z ST , were applied for the rate equation. The experimental results were in very good agreement with the derived rate equation.