Nitric oxide ions, decomposition

The exceptional activity exhibited by ion-exchanged copper ZSM-5 zeolite catalysts for nitric oxide (NO) decomposition, and for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) in the presence of excess oxygen is well documented [1-10]. The nature of the active copper species in the SCR reaction however still remains uncertain. We and others have recognised that there are two different types of copper species within the ZSM-5 zeolite channels [11]. Isolated copper ions exist in low symmetry environments, and small clusters, where the copper atoms are linked by extra-lattice oxygen species such as [Cu(II)-0-Cu(n)] dimers, are also present. Recent studies have also suggested that the isolated copper ions in ZSM-5 occupy two types of sites [11], which may have different SCR reactivity. It is likely... 

C. Further warming to 65°C forms white iron sulfate monohydrate [17375-41 -6], FeSO H2O, which is stable to 300°C. Strong beating results in decomposition with loss of sulfur dioxide. Solutions of iron(II) sulfate reduce nitrate and nitrite to nitric oxide, whereupon the highly colored [Fe(H20) (N0)] ion is formed. This reaction is the basis of the brown ring text for the quaUtative deterrnination of nitrate or nitrite. 

The reaction in water at pH 7.4 has been much studied since the discovery of the importance of nitric oxide. The products are as for the thermal and photochemical reactions, except that the final product is nitrite ion. This is to be expected since nitric oxide in aerated water at pH 7.4 also yields quantitatively nitrite ion25, by it is believed the series of equations 7-9, which involves oxidation to nitrogen dioxide, further reaction to give dinitrogen trioxide which, in mildly alkaline solution, is hydrolysed to nitrite ion. Under anaerobic conditions it is possible to detect nitric oxide directly from the decomposition of nitrosothiols using a NO-probe electrode system26. Solutions of nitrosothiols both in... 

The superoxide oxide radical interacts with nitric oxide to produce peroxynitrite at a rate which three times faster than the rate at which superoxide dismutase utilizes superoxide (Beckman, 1994). Peroxynitrite is capable of diffusing to distant places in neural cells where it induces lipid peroxidation and may be involved in synaptosomal and myelin damage (Van der Veen and Roberts, 1999). After protonation and decomposition, peroxynitrite produces more hydroxyl radicals. This mechanism of hydroxyl radical generation is not dependent on redox active metal ions and may be involved in initiating lipid and protein peroxidation in vivo (Warner et al., 2004). 

The effect of electrical fields on the radiolysis of ethane has been examined by Ausloos et and this study has shown that excited molecules contribute a great deal to the products. The experiments were conducted in the presence of nitric oxide, and free-radical reactions were therefore suppressed. The importance of reactions (12)-(14) was clearly demonstrated by the use of various isotopic mixtures. Propane is formed exclusively by the insertion of CH2 into C2H6 and the yield is nearly equal to the yield of molecular methane from reaction (14). Acetylene is formed from a neutral excited ethane, probably via a hot ethylidene radical. Butene and a fraction of the propene arise from ion precursors while n-butane appears to be formed both by ionic reactions and by the combination of ethyl radicals. The decomposition of excited ethane to give methyl radicals, reaction (15), has been shown by Yang and Gant °° to be relatively unimportant. The importance of molecular hydrogen elimination has been shown in several studies ° °. ... 

Zhang, Y., and M. Flytzani-Stephanopoulos, 1994, Catalytic decomposition of nitric oxide over promoted copper-ion-exchanged ZSM-5 zeolites, in Environmental Catalysis, ed. J.M. Armor, Vol. 552 of ACS Symposium Series (American Chemical Society, Washington, DC) pp. 7-21. 

Nitric oxide decomposition and reduction by ammonia, propene or propane were carried out on H-ZSM-5, Cu " ion-exchanged X-type and ZSM-5 zeolites. 

Alkaline earth and rare earth metal cocation effects are reported in this paper for copper ion-exchanged ZSM-5 zeolites used for the catalytic decomposition of nitric oxide in 02- free, 02- rich, and wet streams. Severe steaming (20% H2O) of Na-ZSM-5 at temperatures above 6(X)°C leads to partial vitreous glass formation and dealumination. Unpromoted Cu-ZSM-5 catalysts suffer drastic loss of NO decomposition activity in wet gas streams at 500°C. Activity is partially recovered in dry gas. Copper migration out of the zeolite channels leading to CuO formation has been identified by STEM DX. In Ce/Cu-ZSM-5 catalysts the wet gas activity is greatly improved. CuO particle formation is less extensive and the dry gas activity is largely recovered upon removal of the water vapor. 

When the -anisotropy is small the analysis of the orientation-selective ENDOR experiments benefits from the improved resolution of the different -components at high field, e.g. at W-band. This procedure is well illustrated by work to clarify the structures of the adsorption complexes of nitric oxide (NO) interacting with metal ions in zeolites [50]. These structures are of interest from an applied view to elucidate the catalytic decomposition of NO into N2 and O2 over transition metal... 

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