Iron decomposition catalysts

Hot spot formation witliin tlie reactor can result in catalyst breakdown or physical deterioration of tlie reactor vessel." If tlie endothermic cyanide reaction has ceased (e.g., because of poor catalyst performance), the reactor is likely to overheat. Iron is a decomposition catalyst for hydrogen cyanide and ammonia under the conditions present in the cyanide reactor, and e. posed iron surfaces in the reactor or reactor feed system can result in uncontrolled decomposition, which could in turn lead to an accidaital release by overheating and overpressure. 

It should also be noted that the iron phosphate catalyst is inactive for consecutive decomposition of the produced citraconic anhydride and acetic acid. 

Summary of literature data on methane decomposition catalysts and preferred temperature range. Catalysts 1 = nickel, 2 = iron, 3 = carbon, and 4 = other transition metals (Co, Pd, Pt, Cr, Ru, Mo, W). The dotted line arbitrarily separates heterogeneous (catalytic) and homogeneous (noncatalytic, gas phase) temperature regimes of the methane decomposition reaction. 

The present paper focuses on the interactions between iron and titania for samples prepared via the thermal decomposition of iron pentacarbonyl. (The results of ammonia synthesis studies over these samples have been reported elsewhere (4).) Since it has been reported that standard impregnation techniques cannot be used to prepare highly dispersed iron on titania (4), the use of iron carbonyl decomposition provides a potentially important catalyst preparation route. Studies of the decomposition process as a function of temperature are pertinent to the genesis of such Fe/Ti02 catalysts. For example, these studies are necessary to determine the state and dispersion of iron after the various activation or pretreatment steps. Moreover, such studies are required to understand the catalytic and adsorptive properties of these materials after partial decomposition, complete decarbonylation or hydrogen reduction. In short, Mossbauer spectroscopy was used in this study to monitor the state of iron in catalysts prepared by the decomposition of iron carbonyl. Complementary information about the amount of carbon monoxide associated with iron was provided by volumetric measurements. 

It should be noted that the results for the formic acid decomposition donor reaction have no bearing for ammonia synthesis. On the contrary, if that synthesis is indeed governed by nitrogen chemisorption forming a nitride anion, it should behave like an acceptor reaction. Consistent with this view, the apparent activation energy is increased from 10 kcal/mole for the simply promoted catalyst (iron on alumina) to 13-15 kcal/mole by addition of K20. Despite the fact that it retards the reaction, potassium is added to stabilize industrial synthesis catalysts. It has been shown that potassium addition stabilizes the disorder equilibrium of alumina and thus retards its self-diffusion. This, in turn, increases the resistance of the iron/alumina catalyst system to sintering and loss of active surface during use. 

The effectiveness of the gas-solid mass transfer in a circulating fluidized bed (see Chapter 10) can be reflected by the contact efficiency, which is a measure of the extent to which the particles are exposed to the gas stream. As noted in Chapter 10, fine particles tend to form clusters, which yield contact resistance of the main gas stream with inner particles in the cluster. The contact efficiency was evaluated by using hot gas as a tracer [Dry et al., 1987] and using the ozone decomposition reaction with iron oxide catalyst as particles [Jiang etal., 1991], It was found that the contact efficiency decreases as the particle concentration in the bed increases. At lower gas velocities, the contact efficiency is lower as a result of lower turbulence levels, allowing a greater extent of aggregate formation. The contact efficiency increases with the gas velocity, but the rate of increase falls with the gas velocity. 

Concentrated sulphur acid evaporation and dehydration is performed in a group of two heat exchangers with important exchange surface (up to 1 340 m2) (HX-208). The S03/S02 decomposition reactor (HX-209) is a set of five reactors with two reactive zones. The first one, with a temperature of 875 K requires a platinum catalyst and the second one an iron-oxide catalyst. The operating temperature in the second zone increases up to 1125 K. Due to operating conditions (temperature, chemical composition), these three devices require a nickel-iron-chromium alloy. Then sulphur trioxide recombination reactor consists of a packed column (HX-210). Required investment for S03 conversion is estimated about EUR(08) 508.6 M. 

Lopez P.N., Ramos I.R., Ruiz A.G. A study of carbon nanotube formation by C2H2 decomposition on an iron based catalyst using a pulsed method. Carbon, 2003,41(13), 2509-2517. 

Iron-iron oxide catalysts have been repeatedly reported to lie unsatisfactory for methanol decomposition or oxidation, because of their activity in causing complete oxidation to carbon dioxide or decomposition to carbon if a deficiency of oxygen prevails. However, catalysts composed of iron and molybdenum oxide have been found to be very efficient for methanol oxidation.21 Such a mixed catalyst apparently combines the excellent directive power of molybdenum and the activity of iron. Molybdenum oxide deposited on small iron balls was shown to be 100 per cent efficient... 

The decomposition of methanol or ethanol on an iron-cobalt catalyst deposited on a zeolite substrate represents a transition to the CVD methods (Section 3.3.1.5). Here as well, SWNTs of high purity are obtained. The yields can be up to 800% with reference to the catalyst employed (or 40% relative to the starting material). 

B. Decomposition catalysts may be used when it is not essential that the synthesis be carried out at the lowest possible temperature. These catalysts, prepared by thermal decomposition of various iron salts mixed with appropriate promoters, have a slightly lower activity than corresponding precipitated catalysts. Decomposition catalysts were obtained, in the absence of special carriers, as a powder, suitable for liquid phase suspension units (oil slurry system). 

There are good NH3 decomposition catalysts such as ICI-47-1 (10 weight % nickel on alirmina) Haldor Topsoe DNK-2R (triply promoted iron-cobalt) SUD-Chemie 27-2 (nickel oxide on alirmina) various supported nitrided catalysts (e.g. molybdenum nitride and nickel molybdenum nitride on - a alumina) and ruthenium modified nickel oxide on alumina. 

Iron-zeolite catalysts present an important type of materials with broad application for selective oxidations (i.e. benzene hydroxylation) and environmentally important processes, like SCR reduction of NOx or N2O decomposition. In the case of SCR reaction they could provide a convenient substitution of the vanadia-based system using environmentally problematic ammonia, by more convenient paraffin as a reducing agent. Unfortunately, the efficiency in utilization of paraffin is inferior in comparison to ammonia, namely due to paraffin nonselective oxidation by oxygen catalyzed by unspecified iron-oxide type species typically present in the iron-zeolite catalysts. The mostly used preparation processes include impregnation from water solutions, ion exchange procedures, both in water solution or solid state, as well as gas phase CVD. 

The results presented evidence possibilities of tailoring uniform iron sites in FeMFI zeolites, under specific synthesis and activation conditions. Preparation of steam-activated Fe-silicalite containing mainly isolated iron species in extraffamework positions is essential to derive stmcture-activity relationships in various N2O conversion reactions over iron zeolite catalysts. The activity of the cluster-free Fe-silicalite was significantly higher in N2O reduction with CaHg and CO. However, some level of association of iron species leads to higher activities in direct N2O decomposition. Due to the intrinsic reaction mechanism, this result demonstrates the sensitivity of reactions for the form of the iron species in Fe-zeolites, rather than the existence of a unique active site. 

Sodium acetyfide prepared by this method is identical with that made as in part B except that it contains slight impurities introduced in the sodium amide, chiefly decomposition products of the iron salt catalyst. However, since preparation of sodium amide is not attended by much splashing, this method leaves less unreacted sodium on the... 

Terlecki-Baricevic, A., Cupic, Z., Anic, S., Kolar-Anic, Lj., Mitrovski, S., and Ivanovic, S., Polyvinylpyridine supported iron (III) catalyst in hydrogen peroxide decomposition, J. Serb. Chem. Soc., 60, 969 979, 1995. 

The mechanism of the catalyzed shift reaction for both copper- and iron-based catalysts remains controversial. Two types of mechanism have been proposed adsorptive and regenerative. In the former, the reactants adsorb on the catalyst surface, where they react to form surface intermediates such as formates, followed by decomposition to products and desorption from the surface. In the regenerative mechanism, on the other hand, the surface undergoes successive oxidation and reduction cycles by water and carbon monoxide, respectively to form the corresponding hydrogen and carbon dioxide products of the WGS reaction. 

---