Metal oxides, catalysts decomposition

Chemical Properties. On thermal decomposition, both sodium and potassium chlorate salts produce the corresponding perchlorate, salt, and oxygen (32). Mixtures of potassium chlorate and metal oxide catalysts, especially manganese dioxide [1313-13-9] Mn02, are employed as a laboratory... 

Screening of metal oxide catalysts for carbon nanotubes and hydrogen production via catalytic decomposition of methane... 

The decomposition of nitrous oxide over various metal oxides has been widely investigated by many investigators (1-3). Dell, Stone and Tiley (4) have compared the reactivity of metal oxides and shown that in general p-type oxides were the best catalysts and n-type the worst, with insulators occupying an intermediate position. It has been generally accepted (5) that this correlation indicates that the electronic structure of the catalyst is an important factor in the mechanism of the decomposition of nitrous oxide over metal oxides catalysts. The reaction is usually written (4) as... 

It is also known that a metal oxide such as manganese oxide (Mn02) is effective for decomposition of H202. Ar. attempt to obtain 02 was carried out using metal oxide catalysts without photoirradiation. 

As discussed above, FSEC s S-NH3 cycle also utilizes decomposition of sulfuric acid as the endothermic step for the absorption of solar thermal heat and production of oxygen. However, high temperature concentration and decomposition of sulfur acid presents daunting materials of construction issues. Like the metal sulfate based TCWSCs, it is possible to modify the S-NH3 cycle and do without the decomposition of H2SO4. There are two ways to accomplish this. The first approach is to decompose ammonium sulfate produced in the hydrogen production step of the S-NH3 cycle (Reaction (111)) to a metal sulfate in the presence of a metal oxide catalyst. The second approach is to convert ammonium sulfate to metal pyrosulfate e.g. Zto 20i)-... 

Figure 6.5 shows the yields ([wt%]) of the reaction of PET using several transition metal oxide catalysts under the following conditions a temperature of 500°C, a time factor (the ratio of the mass of the catalyst W, to the PET feed rate F) of 0.317 h, and a particle size of 0.21-0.25 mm. Fc203 did not show activity, hence these results have been omitted. With respect to the reduction of terephthalic acid, FeOOH, nickel hydroxide and nickel oxide showed the decomposition activity of terephthahc acid. However, a large amount of benzoic acid, which is also a sublimate material (sublimation point 100°C), was produced over nickel hydroxide and nickel oxide. Because these nickel compounds are more expensive than FeOOH, FeOOH was considered to be a suitable catalyst for the decomposition of terephthalic acid. 

Selectivity on metal oxide catalysts is ultimately determined by complex intermolecular and surface-adsorbate interactions. Competing reaction channels are facilitated or hindered by the coordination geometry around metal cations, the ease of reduction of the surface, and the resulting stabilization of surface intermediates. The decomposition of relatively simple organic molecules like methanol and formic acid can be surprisingly complex, but attention to a few concepts may help to understand the reaction processes ... 

One of the simplest methods of preparation is by decomposition of a thermally unstable compound. The nitrate or chloride is often preferred, sulphates tend to decompose at higher temperatures. Where the presence of residual traces of anion is to be avoided, the metal salts of organic acids are particularly useful. Formates, oxalates, acetates etc, decompose at low temperatures and often reduce the metal at the same time. For the preparation of catalysts from anions, the ammonium salt is frequently used. Metallic salts of complex acids can be used as a source of metal oxide mixtures. Decomposition of the appropriate chromate, tungstate, molybdate or vanadate will produce the mixed oxide. 

In mixtures of metal and metal oxide catalysts, generally anything that can be done to promote or bring about more intimate contact between the materials will result in an improved catalyst. Although this may be obvious, sometimes it may not be fully appreciated. This point may h illustrated in the preparation of coppen-zinc oxide catalysts. If the efficiency of the coprecipitated hydroxides of copper and zinc is rated as 100, other methods of preparation compare as shown in Table 10-14 when studying the decomposition of methanol. 

Using the same reactor configuration, Simionescu et al. examined the modification of thermal decomposition products of a series of polymers, including polyethylene and polypropylene, using a series of metal oxide catalysts. The effects of Mn02/K20 and Cr203/K20 catalysts were similar the amount of gaseous products was increased and the amount of condensable products was decreased with the addition of the catalyst. However, the effect was not nearly as dramatic as when acid catalysts, such as mordenite and ZSM-5, were used. 

Haneda, M., Tsuboi, G., Nagao, Y., Kintaichi, Y., Hamada, H. (2004). Direct decomposition of NO over alkaline earth metal oxide catalysts supported on cobalt oxide. Catalysis Letters, 97, 145-150. 

Rakovsky, S. K. Cherneva, D. R. Spozhakina, A. A. Novakov, K.. Catalytic Decomposition of Ozone over Suported Metal Oxide Catalysts. 8-Th Intern. Symp. Heter. Catal, Varana, 5-9 October, 1996, p. 407 13. 

Ai M (1977) Activities for the decomposition of formic acid and the acid-base properties of metal oxide catalysts. J Catal 50 291-300 Al-Owais AA, Ballantine JA, Purnell JH, Thomas JM (1986) Thermogravimetric study of the intercalation of acetic acid and of water by AP -exchanged montmorillonite. J Mol Catal 35 201-212... 

Transition metal nitrate hydrates are industrially favored precursors for the preparation of supported metal (oxide) catalysts because of their high solubility and facile nitrate removal. The final phase and particle size depend on the experimental conditions, as reported for both supported and unsupported metal nitrates [1-3]. Several authors report that decreasing the water partial pressure during the decomposition of unsupported nickel nitrate hexahydrate, via vacuum or a high gas flow, increases the final NiO surface area [3, 4], The low water partial pressure results in dehydration of the nickel nitrate hydrate to anhydrous nickel nitrate followed by decomposition to NiO. Decomposition at higher particle pressures, however, occitrred through the formation of intermediate nickel hydroxynitrates prior to decomposition to NiO. Thus, NiO obtained via intermediate nickel hydroxynitrate species showed a poorer siuface area (1 m /g) compared to NiO obtained via anhydrous nickel nitrate species (10 mVg) [4]. 

FIG. 2 Hydrogen peroxide decomposition at 20 C over Ni/Fe and Cu/Fe binary metal oxide catalysts... 

The second reaction is favoured by sunlight and by catalysts such as platinum black or metallic oxides (cf. the decomposition of... 

Formic acid can decompose either by dehydration, HCOOH — H2O + CO (AG° = —30.1 kJ/mol AH° = 10.5 kJ/mol) or by dehydrogenation, HCOOH H2 + CO2 (AG° = —58.6 kJ/mol AH° = —31.0 kJ/mol). The kinetics of these reactions have been extensively studied (19). In the gas phase metallic catalysts favor dehydrogenation, whereas oxide catalysts favor dehydration. Dehydration is the predominant mode of decomposition ia the Hquid phase, and is cataly2ed by strong acids. The mechanism is beheved to be as follows (19) ... 

The reaction is carried out over a supported metallic silver catalyst at 250—300°C and 1—2 MPa (10—20 bar). A few parts per million (ppm) of 1,2-dichloroethane are added to the ethylene to inhibit further oxidation to carbon dioxide and water. This results ia chlorine generation, which deactivates the surface of the catalyst. Chem Systems of the United States has developed a process that produces ethylene glycol monoacetate as an iatermediate, which on thermal decomposition yields ethylene oxide [75-21-8]. 

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