Direct catalytic decomposition

Direct catalytic decomposition of water ( thermo-physical cycle ) ... 

There is an important number of commercial approaches to NO removal, including adsorptive, thermal and catalytic techniques (Armor 1994, Centi and Forzatti 1995, Fritz and Pitchon 1997). In the case of catalytic processes, the elimination of NO can be carried out by direct catalytic decomposition, or by selective catalytic reduction (SCR) using hydrocarbons or ammonia as reductant. Although several catalytic system have been studied, zeolites have been proposed as interesting catalysts for both reactions. 

Several techniques have been considered to decrease NOx emission, such as selective noncatalytic reduction (SNCR), selective catalytic reduction (SCR) with ammonia (NH3) or hydrocarbon, and direct catalytic decomposition of NO. The main disadvantage of the SCR process is the high cost associated with the consumption of reductants. Nevertheless, direct catalytic decomposition of NO without the addition of reducing agents is an effective and economical procedure to decrease NOx emission. Therefore, the direct decomposition of NO into N2 and O2 (2NO = N2 + O2) is the optimal way for NO removal, because the process is simple and there is no necessity for a reductant such as a hydrocarbon, NH3, or urea. 

The rate of decomposition of hydrazine in stainless steel vessels (which is accompanied by corrosion) is directly proportional to carbon dioxide concentration over 20 ppm and below 250 ppm. The species responsible for the catalytic decomposition is not one of the expected corrosion products, iron(II) carbazate or its nickel or chromium(II) analogues. 

Despite several decades of studies devoted to the characterization of Fe-ZSM-5 zeolite materials, the nature of the active sites in N20 direct decomposition (Fe species nuclearity, coordination, etc.) is still a matter of debate [1], The difficulty in understanding the Fe-ZSM-5 reactivity justifies a quantum chemical approach. Apart from mononuclear models which have been extensively investigated [2-5], there are very few results on binuclear iron sites in Fe-ZSM-5 [6-8], These DFT studies are essentially devoted to the investigation of oxygen-bridged binuclear iron structures [Fe-0-Fe]2+, while [FeII(p-0)(p-0H)FeII]+ di-iron core species have been proposed to be the active species from spectroscopic results [9]. We thus performed DFT based calculations to study the reactivity of these species exchanged in ZSM-5 zeolite and considered the whole nitrous oxide catalytic decomposition cycle [10],... 

D. Ballou, G. Palmer, and V. Massey, Direct demonstration of superoxide anion production during the oxidation of reduced flavin and of its catalytic decomposition by erythrocuprein. Biochem. Biophys. Res. Commun. 36, 898-904 (1969). 

Effective double stereodifferentiation is possible in intramolecular C-H insertion.199 For example, catalytic decomposition of enantiopure (lY,2Y)-diazoacetate 74 by Rh2(4A-MEOX)4 directed the reaction toward the preferential formation of y-lactone (lY)-75, whereas the corresponding reaction catalyzed by Rh2(4i -MEOX)4 prefers initially forming y-lactone (lY)-76 (Equation (66)). Similarly, treatment of (lY,2i )-diazoacetate 77 with Rh2(5A-MEPY)4 or Rh2(4i -MPPIM)4 gave (lY)-78 or (lY)-79, respectively (Equation (67)).199... 

Iron(III) weso-tetraphenylporphyrin chloride [Fe(TPP)Cl] will induce the autoxidation of cyclohexene at atmospheric pressure and room temperature via a free radical chain process.210 The iron-bridged dimer [Fe(TPP)]2 0 is apparently the catalytic species since it is formed rapidly from Fe(TPP)Cl after the 2-3 hr induction period. In a separate study, cyclohexene hydroperoxide was found to be catalytically decomposed by Fe(TPP)Cl to cyclohexanol, cyclohexanone, and cyclohexene oxide in yields comparable to those obtained in the direct autoxidation of cyclohexene. However, [Fe(TPP)] 20 is not formed in the hydroperoxide reaction. Furthermore, the catalytic decomposition of the hydroperoxide by Fe(TPP)Cl did not initiate the autoxidation of cyclohexene since the autoxidation still had a 2-3 hr induction period. Inhibitors such as 4-tert-butylcatechol quenched the autoxidation but had no effect on the decom-... 

Of particular interest are catalytic methane decomposition reactions producing special (e.g. filamentous) forms of carbon. For example, researchers have reported catalytic decomposition of methane over Ni catalyst at 500°C with the production of hydrogen and whisker carbon26 and concentrated solar radiation was used to thermally decompose methane into hydrogen and filamentous carbon.27 The advantages of this system included efficient heat transfer due to direct irradiation of the catalyst, and C02-free operation. 

Mass spectra can only be obtained from compounds which are in the vapor-phase. The vapor pressure required to obtain a spectrum depends on the kind of sample introduction system if the sample is first evaporated in the gas container of the spectrometer and from there introduced into the ion source, a vapor pressure of about 10-2 mm Hg is necessary, while for direct introduction of the substance into the ion source a vapor pressure of only 10-6 mm is needed,2 usually sufficient to obtain spectra of very polar and nearly nonvolatile compounds, e.g., amino acids. Therefore, direct introduction systems2-9 (see also Biemann,10 p. 33) available since the pioneering work of Reed2 in all commercial instruments should be used in spite of experimental difficulties, if thermal or catalytic decomposition of the sample is to be expected. If the vapor pressure is so low that the sample cannot be vaporized sufficiently in the ion source, protecting of polar OH and NH groups by methylation or acetylation may produce a derivative of volatility enough to obtain a spectrum. 

The direct catalytic, oxidation method of ethylene is described in Ref 17, pp 77—87 Explosibility. Liquid ethylene oxide is stable to detonating agents, but the vapor will undergo explosive decomposition. Pure ethylene oxide vapor will decompose partially however, a slight dilution with air or a small increase in initial pressure provides an ideal condition for complete decomposition. Copper or other acetylide-forming metals such as silver, magnesium, and alloys of such metals should not be used to handle or store ethylene oxide because of the danger of the possible presence of acetylene. Acetylides detonate readily and will initiate explosive decomposition of ethylene oxide vapor. In the presence of certain catalysts, liquid ethylene oxide forms a poly-condensate. 

---