Iron oxide-based catalyst

Dehydrogenation, Ammoxidation, and Other Heterogeneous Catalysts. Cerium has minor uses in other commercial catalysts (41) where the element s role is probably related to Ce(III)/Ce(IV) chemistry. Styrene is made from ethylbenzene by an alkah-promoted iron oxide-based catalyst. The addition of a few percent of cerium oxide improves this catalyst s activity for styrene formation presumably because of a beneficial interaction between the Fe(II)/Fe(III) and Ce(III)/Ce(IV) redox couples. The ammoxidation of propjiene to produce acrylonitrile is carried out over catalyticaHy active complex molybdates. Cerium, a component of several patented compositions (42), functions as an oxygen and electron transfer through its redox couple. 

The results of catalytic activities in the dehydrogenation of ethylbenzene with various iron oxide based catalysts are shown in Fig. l(a-b). The number in the parentheses of the catalyst codes indicates the weight fi-action of metal per gram carbon. On oxidized CNF alone less than 20% conversion of EB is observed after 3 h on stream. The conversion of ethylbenzene... 

Large amounts of styrene are commercially produced by dehydrogenation of ethylbenzene (EB) in the presence of steam using iron oxide-based catalysts. Carbon dioxide, small amounts of which are formed as a by-product in the ethylbenzene dehydrogenation, was known to depress the catalytic activity of commercial catalyst [7,8]. However, it has been recently reported that several examples show the positive effect of carbon dioxide in this catalytic reaction [5,9,10]. In this study, we investigated the effect of carbon dioxide in dehydrogenation of ethylbenzene over ZSM-5 zeolite-supported iron oxide catalyst. 

Dehydrogenation of ethylbenzene over iron oxide-based catalyst in the presence of carbon dioxide... 

The iron oxide-based catalysts were prepared by Figure 1. Pathways of dehy-a coprecipitation method. In a typical experiment, drogenation of ethylben-1.4 g of catalyst (0.18-0.30mm) was set in a quartz tube reactor. Ethylbenzene was fed through a vaporizer, and was mixed with CO2. The flow rate was 130 ml/min. The dehydrogenation was conducted at 550 °C under atmospheric pressure. The product was analyzed by GC. ... 

Figure 4 shows that activities of several kinds of iron oxide based catalysts. A Fe/Ca/Al oxides catalyst exhibited the best performance among the catalysts tested. Fe/Ca/Al and Fe/Al oxides catalysts were highly active, whereas Fe/Ca and Ca/Al oxides catalyst were extremely low in activity. The selectivities of Fe/Al oxides and Fe/Ca/Al oxides catalysts were almost the same (97% at 5.25 h), and the main by-products were benzene and toluene. Therefore the addition of an optimum amount of CaO to Fe/Al based catalyst could suppress the deactivation of the catalyst during long term reaction. Further experiment are under achievement to elucidate precisely the role of CaO. 

Bahlbro, H. An investigation on the kinetics of the conversion of CO with H2O over iron oxide based catalysts. In The Haldor Topsoe Laboratory Gjellerup Copenhagen, 1969. 

Bohlbro, H., "An Investigation on the Kinetics of the Conversion of Carbon Monoxide with Water Vapour Over Iron Oxide Based Catalysts," (2nd ed). Gjellerup, Copenhagen, 1969. 

Several experimental studies have been performed to validate this model. This mechanism was mainly validated by Boreskov et al. [3]. They directly measured the oxidation and reduction of an iron oxide-based catalyst with CO and H2O. They concluded that the catalyst surface is reduced and oxidized by the CO and H2O and the rate of reactions is in good agreement with the rate conversion of CO in the WGSR. 

Early reports on this reaction were focused on iron oxide-based catalysts, supported on different supports alumina, zeolite, and active carbon, among others. Later, hydrotalcite-like compounds, and the topical V-Mg-0 catalysts were explored. Park and his group, one of the most active in this field, first reported the use of zirconia as a catalyst, " and later on that of ceria-zirconia-based catalysts and vanadium-antimony oxide-based catalysts. Publications up to 2007 have been subject of several reviews. Therefore, the most relevant feamres will be revised hereinafter, as well as more recent publications, and the reader is invited to get further details in the aforementioned reviews. 

Ji M, Chen G, Wang J, Wang X, Zhang T (2010) Dehydrogenation of ethylbenzene to styrene with CO2 over iron oxide-based catalysts. Catal Today 158 464-469... 

Zhu XM, Schon M, Bartmann U, van Veen AC, Muhler A (2004) The dehydrogenation of ethylbenzene to styrene over a potassium-promoted iron oxide-based catalyst a transient kinetic study. Appl Catal Gen 266 99-108... 

Actually, iron oxide based catalysts are the most widespread contacts utilized in industrial dehydrogenation of ethylbenzene (EB) to styrene, and many propositions how to enhance their efficiency are still reported in the literature (refs. 1-3). A majority of the propositions has concerned, however, promoters variation rather than proper selection of the main components of the initial mixture from which the catalyst is prepared. The latter problem seems to be of importance because of a consolidating opinion that just Ee atoms are included, apart from 0 and K atoms, into such proposed active phases of the catalyst as KFe02 (ref. 4), solid solution of potassium in -Fe20j... 

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