Catalytic properties and chemical stability of potassium polyferrites with the addition of four-charged cations

Abstract

In order to elucidate the effect exerted by the addition of four-charged cations on the composition, chemical stability and catalytic properties, samples of potassium polyferrites with the β′′-alumina type structure of the composition K2FeII1+qFeIII10–2q MeqIVO17, where Me is Ce, Ti, Zr, and q = 0÷1.0, were synthesized. The mechanism of the effect of four-charged cations on the activity, selectivity of action and corrosion resistance of β′′-potassium polyferrite has been determined. Polyferrites doped with four-charged cations are characterized by a decrease in the specific rate of styrene formation and an increase in the selectivity of action in the ethylbenzene dehydrogenation reaction. The destabilizing effect of titanium additives is revealed, which is expressed in facilitating the emission of an alkali metal from the crystal lattice of polyferrite. Cerium additives lead to the destruction of the polyferrite structure due to the reduction of Ce4+ → Се3+ at the q parameter values above 0.6. Zirconium additives do not reduce the corrosion resistance of ferrite systems under the conditions of the dehydrogenation reaction.

Formation of a ceramic structure of promoted iron oxide catalyst

“…However, our data correlate with the results obtained by many other researchers [32], and indicate a high carburisation of such catalyst surface and its low selectivity. The introduction of an alkali metal promoter into the system significantly increases the contact activity [1][2][3][4][6][7][8][9].…”

“…Furthermore, alloying additives are usually introduced into the industrial catalyst, improving the performance properties of the final product -the catalyst [2,4,7,[11][12]. We selected zirconium as an alloying additive.…”

“…Dehydrogenation of olefinic and alkylaromatic hydrocarbons is a multi-tonnage process. It is conducted with the use of promoted iron oxide catalysts [1][2][3][4][5][6][7][8][9][10]. The minimum set of parameters determining the effectiveness of the catalyst, in addition to the catalytic characteristics, always includes the size of the available pore surface, the thermal stability of the contact porous structure, and the mechanical strength of the catalyst granules.…”

“…In the promoted iron oxide catalysts for the dehydrogenation of alkylaromatic hydrocarbons, the mass content is: iron oxide -60-70%; potassium compounds in terms of K2O -10-15%. There are also various additives providing the increased selectivity, thermal stability, mechanical strength, and durability [2][3][4][5][6][7][8][9].…”