Iron oxide catalysts ferrites

Two or more soHd catalyst components can be mixed to produce a composite that functions as a supported catalyst. The ingredients may be mixed as wet or dry powders and pressed into tablets, roUed into spheres, or pelletized, and then activated. The promoted potassium ferrite catalysts used to dehydrogenate ethylbenzene in the manufacture of styrene or to dehydrogenate butanes in the manufacture of butenes are examples of catalysts manufactured by pelletization and calcination of physically mixed soHd components. In this case a potassium salt, iron oxide, and other ingredients are mixed, extmded, and calcined to produce the iron oxide-supported potassium ferrite catalyst. 

Iron-based oxide mixtures, e.g. ferrites, and supported iron oxides can be very effective catalysts for the dehydrogenation of butene to butadiene, as also appears from the patent literature [160],... 

Iron oxide is an important component in catalysts used in a number of industrially important processes. Table I shows some notable examples which include iron molybdate catalysts in selective oxidation of methanol to formaldehyde, ferrite catalysts in selective oxidative dehyrogenation of butene to butadiene and of ethylbenzene to styrene, iron antimony oxide in ammoxidation of propene to acrylonitrile, and iron chromium oxide in the high temperature water-gas shift reaction. In some other reactions, iron oxide is added as a promoter to improve the performance of the catalyst. 

The success of the correlation of catalytic behavior with bulk Mossbauer parameters by Skalkina et al. is also reflected in the work of Tops0e and Boudart (96). As discussed earlier, these authors found a decrease in the isomer shift of the octahedral iron ions in a lead-promoted Cr-Fe304 carbon monoxide shift catalyst, indicative of an increased covalency of these ions. Schwab et al. (203) have proposed a correlation of the activity for CO oxidation by ferrites with the octahedral ions in these materials, and the electron transfer required for this catalytic process may be facilitated by an increased covalency of the metal ions (204). In view of these suggestions, the lead-promoted catalyst is expected to possess a higher catalytic activity for the CO shift reaction than an unpromoted catalyst, as evidenced by the Mossbauer parameters of these two samples. This has in fact been shown experimentally to be the case (96). For the reverse CO shift reaction over supported europium (176), the success of the correlation between catalytic activity and the Mossbauer parameters (in this case the reducibility) has already been noted in Section III, A, 4. 

Use Iron oxide pigment other iron salts ferrites water and sewage treatment catalyst, especially for synthetic ammonia fertilizer feed additive flour enrichment reducing agent herbicide wood preservative process engraving. 

Fe is the active metal for high-temperature WGS reaction. Hence, we introduced a variety of metal dopants (M = Cr, Mn, Co, Ni, Cu, Zn and Ce) for iron oxide (spinel lattice) and screened their effectiveness for high-temperature WGS reaction [1]. The idea was to examine if ferrite formation can occur with dopants and promote the Fe Fe redox couple. The substitution of Fe sites in the ferrite strucmre with other transition/non-transition/inner transition metal atoms leads to the crystallization of an inverse (or mixed) spinel. The stoichiometry of an inverse spinel can be represented as A(i a)Ba[AaB(2 a)]04, where 8 is the degree of inversion, while A and B represent typical divalent and trivalent cations, respectively. The catalysts were synthesized by coprecipitation method using nitrates as precursors. The synthesized catalysts were evaluated for ultra high temperature WGS reaction in the temperature region 400-550 °C and GHSV 60,000 h- ... 

Iron oxide is produced by the combustion of Fe(CO)5 with excess air. The iron oxide produced is used for a highly transparent red pigment and a highly pure ferrite, Fe304 or > -Fe203 is freely produced with a different treatment temperatures. If Fe(CO)5 is decomposed in a magnetic field, high intensity crystalline iron whiskers are produced and these whiskers are used for composite materials or catalysts [4]. 

Mn-Fe alloy catalysts with 32%-40% of Mn have high activities. The addition of 3%-7% of Ru02 into Fe-based catalyst containing cobalt ferrite (25%-359c of Co), magnesium ferrite (20%-25% of Mg), K2O (0.5%-2%) and iron oxide increases activities and heat-resistant properties of catalysts. ... 

Ammonia synthesis catalysts of increased low-temperature activity, prepared from iron and potassium oxides, cobalt ferrite, and calcium aluminate. V. S. Komarov, P. D. Rabina, and L. M. Dmitrenko. SU 598632 (1978). 

Work on one particular ferritic steel, Fecralloy, for fabrication of catalyst substrates was pioneered by the United Kingdom Atomic Energy Authority at Harwell and Johnson Matthey, in collaboration with Resistalloy, which developed technology for producing thin strip [32]. This and related alloys, in addition to iron, chromium, and aluminum, contain low levels of elements such as yttrium (0.1-3.0%), thought to enhance the protective properties of the surface alumina layer. Alumina forms by the oxidation of bulk... 

When potassium is applied also, a different behaviour is observed for the two oxides. In titania-supported catalysts a mixed compound containing titanium, iron and potassium is formed, probably the non-stoichiometric oxide K(,gFej, jTi, 204 [16]. Since the colour of the samples supported on zirconia after calcination indicated the formation of potassium ferrite (KFeOj), which is known to decompose readily in atmospheric air, diffractograms were recorded excluding air. In these catalysts, however, only excess potassium carbonate was observed, and no diffraction lines emanating from other phases than zirconia were detected. In combination with the results from TEM, it is concluded that a finely distributed phase, most probably potassium ferrite, was formed, in which iron and potassium are intimately mixed. 

Ammonia synthesis catalysts containing iron, potassium, and zirconium oxides, and cobalt and magnesium ferrites. P. D. Rabina, V. S. Komarov, and M. D. Efros. SU 539601 (1977). 

The activity of Fe is decreased by addition of Ni [78, 79], and a Mn-Fe alloy of 30-40 percent Mn gives a high activity [80]. The conventional promoted iron catalyst is further promoted by the addition of Co. The catalysts are prepared by burning a Fe-Co alloy in O2 followed by the addition of promoters [81]. The alloying effect of Fe-Co, and Fe-Ni was studied in detail [82]. The addition of 3-7 wt% RUO2 to a catalyst composed of Co ferrite (25-35%), Mg ferrite (20-25%), K2O (0.5-2%), and Fe oxide (rest%) increases the ammonia activity and heat resistance of the catalyst [83]. 

The same group recently reported the use of a ferrite spinel catalyst (MnFe204), where the iron was partially substituted with Ru and Cu, i.e., MnFe15Ruo.35Cuo.15O4 for the room temperature oxidation of alcohols [66]. However, 20 mol% catalyst (based on ruthenium) was necessary to accomplish even the oxidation of benzyl alcohol. For primary and secondary aliphatic alcohols turnover frequencies of 2 h and 3.5 h, respectively, were the maximum rates achieved. 

According to [7], activity in the methane oxidation is determined by the presence of red-ox sites in catalyst. Probably, for the ferrites active sites are Fe and Mn. Their presence is confirmed by XPS data. The high catalytic activity can be caused by simultaneous presence of manganese and iron, which can change the oxidation state 2Fe(Mn) + Oiattioe 2Fe(Mn) + V2 O2 facilitating the methane oxidatioa... 

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