XPS and TPD characterization of manganese-substituted iron-potassium oxide catalysts which are selective for dehydrogenation of ethylbenzene into styrene

Manganese-substituted (0-100%) iron-potassium oxide (Mn-Fe-K) catalysts which are selective for dehydrogenation of ethylbenzene to styrene were prepared by the alcoxide sol-gel method. They have been characterized by XPS, BET surface area measurement and TPD studies. The differences of surface properties between the Mn-Fe-K catalysts and unsubstituted iron-potassium oxide (Fe-K) catalyst were reasonably reflected in the XPS spectrum of oxygen (O 1s) and potassium (K 2p). The XPS spectra of Mn-Fe-K catalysts based on the binding energy shifts of O 1s is and K 2p bands resembled those of KFeO2 as an active phase for the dehydrogenation of ethylbenzene. On the contrary, the unsubstituted Fe-K catalyst showed the XPS spectra including KOH and Fe3O4 as inactive phases. The presence of Mn ions in the catalyst matrix (gamma -Fe2O3, MnFe2O4) results in stabilization of the KFeO2 active phase, and did not affect catalytic behavior of the K-promoted iron based oxide. The maximum enhancement of catalytic activity at the optimum 20% Mn-substitution is owing to the large surface area, the minimization of carbonaceous deposition, and the retardation of pyrolysis of KFeO2 to KOH and Fe3O4. (C) 2001 Elsevier Science B.V. All rights reserved.