Effect of Doubly Charged Ion Additives on the Activity and Chemical Stability of Catalytically Active Potassium Ferrites
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TALYSIS IN CHEMICAL AND PETROCHEMICAL INDUSTRY
Effect of Doubly Charged Ion Additives on the Activity and Chemical Stability of Catalytically Active Potassium Ferrites L. G. Anikanovaa, * and N. V. Dvoretskiia, ** a
Yaroslavl State Technical University, Yaroslavl, 150023 Russia *e-mail: [email protected] **e-mail: [email protected]
Received July 8, 2019; revised October 7, 2019; accepted October 21, 2019 III III Abstract—Potassium polyferrites K2Fe1II−q MqFe10 O17 (where M is Mg and Zn) and K2–2qFeIIMqFe10 O17 (where M is Ca and Sr; q = 0–0.4) are synthesized to determine the effect of the size of a doubly charged dopant ion on their catalytic properties. The mechanism of the effect of doubly charged cation additives on the activity, selectivity, and corrosion resistance of potassium β'' polyferrite is identified. It is shown for the first time that doubly charged cations are distributed differently in the structure of β'' polyferrite depending on their size: either they are in a spinel-like block and then replace Fe2+ ions, or they replace potassium in interblock space. The Mg2+ and Zn2+ ion additives sharply reduce the catalytic activity and selectivity of β'' polyferrite. Such additives are undesirable. Small amounts of Ca2+ and Sr2+ cations greatly improve the corrosion resistance of the catalysts due to a drop in the mobility of potassium ions within a cation-conducting layer.
Keywords: potassium polyferrites, catalyst, additives, doubly charged cations, activity, selectively, corrosion resistance DOI: 10.1134/S2070050420030022
INTRODUCTION Large amounts of styrene, one of the most important monomers in modern petrochemical industry, are obtained via the dehydrogenation of ethylbenzene on promoted iron oxide catalysts [1]. Iron–potassium oxide catalysts have complex chemical and phase compositions [2, 3], and are used to dehydrogenate olefin hydrocarbons [4]. The mass fraction of iron oxide in industrial promoted iron oxide catalysts for the dehydrogenation of alkyl aromatic hydrocarbons is 60–70%, while that of potassium compounds is 10– 15% per K2O [5, 6]. Compounds of alkali, alkaline earth metals, magnesium, vanadium, cerium, lanthanum, neodymium, titanium, zirconium, chromium, molybdenum, nickel, cobalt, and other elements are used as promoters and additives [1, 5–11]. The mass fraction of additives varies widely, but usually is no more than 15%. Portland cement is also introduced to increase the strength of catalyst pellets [5, 6]. A catalyst is multiphase under the conditions of dehydrogenation [2, 3]. Its phase composition is differs substantially from those of freshly prepared catalyst and catalyst unloaded from a reactor and cooled in air. This was proved for the first time in [12, 13], when the authors found the phase composition of iron–chromium oxide catalysts under the conditions of n-butene dehydrogenation in a high-temperature X-ray chamber with a controllable gas environment. The promoted
iron oxide catalyst for the dehydrogenation of ethylbenzene to styrene is a ferrite system under co
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