Catalysts spinels

Nissinen T, Valo T, Gasik M, Rantanen J, Lampinen M. Microwave synthesis of catalyst spinel MnCc>204 for alkaline fuel cell. J Power Sources 2002 106 109-15. 

The predominant process for manufacture of aniline is the catalytic reduction of nitroben2ene [98-95-3] ixh. hydrogen. The reduction is carried out in the vapor phase (50—55) or Hquid phase (56—60). A fixed-bed reactor is commonly used for the vapor-phase process and the reactor is operated under pressure. A number of catalysts have been cited and include copper, copper on siHca, copper oxide, sulfides of nickel, molybdenum, tungsten, and palladium—vanadium on alumina or Htbium—aluminum spinels. Catalysts cited for the Hquid-phase processes include nickel, copper or cobalt supported on a suitable inert carrier, and palladium or platinum or their mixtures supported on carbon. 

Many late transition metals such as Pd, Pt, Ru, Rh, and Ir can be used as catalysts for steam reforming, but nickel-based catalysts are, economically, the most feasible. More reactive metals such as iron and cobalt are in principle active but they oxidize easily under process conditions. Ruthenium, rhodium and other noble metals are more active than nickel, but are less attractive due to their costs. A typical catalyst consists of relatively large Ni particles dispersed on an AI2O3 or an AlMg04 spinel. The active metal area is relatively low, of the order of only a few m g . ... 

With respect to non-noble and non-Ru catalysts, transition metal chalcogenides with spinel and pyrite structures have been investigated and shown that these can also be active to oxygen reduction processes. The motivation in the present case is that chalcogen addition might enhance the stability and activity toward the ORR... 

In these soak (300°C)-ramp (up to 900°C) /min) mode tests, a O.lOg of sulfated DESOX sample—the leading catalyst based on magnesium aluminate spinel with an excess MgO catalyzed with Ce and V oxides [9]—was allowed to react with either Hj (5%)/Ar (50 ml/min), undiluted H (70 ml/min) or CH (14 ml/min). 

Due to the formation of Ca/Al mixed oxide on the surface, the Ca -modified alumina has a completely different structure compared to the spinel one This leads to a different type of surface Lewis acid/basic sites, rendering the catalyst 30 times less active. 

Cobaltites with spinel stractnre have compositions MC02O4, where M is a metal forming divalent cations, snch as zinc, cadminm, magnesinm, nickel, manganese, and divalent cobalt. In contrast to the perovskites, the cobaltites have a rather high catalytic activity already at room temperatnre. Experiments show that the activity increases with increasing spinel structure content (i.e., increasing number of Co ions) of the catalyst snrface. The trivalent cobalt ions promote the withdrawal of... 

It is interesting to note that cobalt cobaltite, C03O4, is a good catalyst, too, for anodic chlorine evolution. In this case, too, a correlation is observed between the reaction rate and the spinel s defect concentration (amount of nonstoichiometric oxygen). 

It is known that some spinel-structured 3d-metal oxides are good catalysts for many processes involving electron transfer [12]. However, their low conductivity does not allow for the direct use in the electrode of the battery, and grafting them onto the carbon matrix is also very difficult technical problem. It was found recently that this problem could be solved indirectly, creating the spinel catalytic centers on the surface of carbon by means of adsorption of some 3d-metal complexes on the graphite surface followed by subsequent pyrolysis at certain temperatures [13,14],... 

Soled S.L., Iglesia E., and Fiato R.A. 1992. Copper-promoted cobalt manganese spinel catalyst and method for making the catalyst for Fischer-Tropsch synthesis. U.S. Patent 5162284. 

Fig. 3 Raman spectra of Co/y-Al203 and CoRu/y-Al203 after different pretreatments, CoO, C03O4 (spinel), and CoA1204 (spinel).26 Reprinted from Journal of Catalysis, Vol. 204, J. Jongsomjit, J. Panpranot and J. G. Goodwin, Jr, Co-Support compound formation in alumina-supported cobalt catalysts, pp. 98-109. Copyright (2001), with permission from Elsevier.

C02 — 12.5 mol % space velocity 6400 h 1, the CO conversion rate was found to depend very strongly on the calcination temperature of the catalyst. For example, a catalyst calcined at 500 °C achieved only 25% conversion by 350 °C, while a catalyst calcined at 900 °C achieved 80% conversion by 225 °C. The authors suggested that the Cu-Mn spinel oxide was more easily reducible after high temperature calcination treatment based on a TPR study, allowing for a greater number of highly dispersed Cu species, as verified by XRD. The optimum Cu/Mn ratio was found to be 1/2. 

Figure 1.9 TG, DTG, and DTA profiles for an amorphous catalyst precursor obtained by coprecipitation of Fe(N03)3 and Mg(N03)2 in solution [65], This precursor is heated at high temperatures to produce a MgFe204 spinel, used for the selective oxidation of styrene. The thermal analysis reported here points to four stages in this transformation, namely, the losses of adsorbed and crystal water at 110 and 220°C, respectively, the decomposition and dehydroxylation of the precursor into a mixed oxide at 390°C, and the formation of the MgFe204 spinel at 640°C. Information such as this is central in the design of preparation procedures for catalysts. (Reproduced with permission from Elsevier.)...

O2 and H2 dissociation kinetics are better at higher temperatures (>400 °C), low-cost electrode structures of high surface area Ni and oxides such as spinels or perovskites to replace the very effective, but costly, Pt catalysts have been sought. 

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