OXIDATION OF NO

The oxidation of terminal alkenes with an EWG in alcohols or ethylene glycol affords acetals of aldehydes chemoselectively. Acrylonitrile is converted into l,3-dioxolan-2-ylacetonitrile (69) in ethylene glycol and to 3,3-dimetho.xy-propionitrile (70) in methanol[28j. 3,3-Dimethoxypropionitrile (70) is produced commercially in MeOH from acrylonitrile by use of methyl nitrite (71) as a unique leoxidant of Pd(0). Methyl nitrite (71) is regenerated by the oxidation of NO with oxygen in MeOH. Methyl nitrite is a gas, which can be separated easily from water formed in the oxidation[3]. 

A high pressure level results in a higher energy requirement with possibly higher utility eosts. On the other hand, today s striet environmental pollution laws with regard to NOx diseharged into the atmosphere are easier to meet at higher pressures, and oxidation of NO to NO2 is favored by inereased pressure and low temperature. 

Reaction (12-9) shows the photochemical dissodation of NO2. Reaction (12-10) shows the formation of ozone from the combination of O and molecular O2 where M is any third-body molecule (principally N2 and O2 in the atmosphere). Reaction (12-11) shows the oxidation of NO by O3 to form NO2 and molecular oxygen. These three reactions represent a cyclic pathway (Fig. 12-4) driven by photons represented by hv. Throughout the daytime period, the flux of solar radiation changes with the movement of the sun. However, over short time periods (—10 min) the flux may be considered constant, in which case the rate of reaction (12-9) may be expressed as... 

The cycle represented by Eqs. (12-9), (12-10), and (12-11) is illustrated by the upper loop (a) in Fig. 12-4. In this figure, the photolysis of NOj by a photon forms an NO and an O3 molecule. If no other chemical reaction is occurring, these two species react to form NOj, which can start the cycle over again. In order for the O3 concentration to build up, oxidizers other than O3 must participate in the oxidation of NO to form NOj. This will... 

Moehida, I., Kawabuehi, Y., Kawano, S., Matsumura, Y. and Yoshikawa, M., High catalytic activity of pitch-based activated carbon fibres of moderate surface area for oxidation of NO to NOj at room temperature. Fuel, 1997, 76(6), 543 548. 

Let s write the rate laws for the steps in a mechanism proposed for the gas-phase oxidation of NO to N02. Its overall rate law has been determined experimentally ... 

Hydroxyl, OH, acts as a catalyst for the oxidation of NO to NO2. NO2 molecules can react with the OH radical to produce HNO3, which may be removed in precipitation. This is how most tropospheric NO, eventually gets removed, either in wet or dry deposition. 

The hexamine cobalt (II) complex is used as a coordinative catalyst, which can coordinate NO to form a nitrosyl ammine cobalt complex, and O2 to form a u -peroxo binuclear bridge complex with an oxidability equal to hydrogen peroxide, thus catalyze oxidation of NO by O2 in ammoniac aqueous solution. Experimental results under typical coal combusted flue gas treatment conditions on a laboratory packed absorber- regenerator setup show a NO removal of more than 85% can be maitained constant. 

Indeed, given an improperly designed or understood system, a blocking agent, like ascorbic acid, could be catalytic toward nitrosamine formation. For example, if the source of nitrosatlng agent is nitrite ion and the susceptible amine is in the lipid phase, conceivably ascorbic acid could cause the rapid reduction of nitrite ion to nitric oxide which could migrate to the lipid phase. Subsequent oxidation of NO to NO in the lipid phase could cause nitrosation. 

For Ti02 and Z1O2, it is well known that sulfation induces a strong increase of acidity [17] and the participation of an add mechanism could then account for this promotion of activity. This mechamsm can be described as a bifunctional process oxidation of NO to NO on Cu sites, and nitration of a product of the oxidation of decane on the acid fiinction(8). The preparation of the catalyst must have a great influence on the activity. This has been shown by the comparison of three Cu/TiC catalysts prepared in different conditions one in which titania is first treated with sulfuric acid, then by Cu acetate (denominated Cu 04/Ti02, containing 0.S wt% Cu, 0.6 wt% S), one in which Cu is... 

An in situ infrared investigation has been conducted of the reduction of NO by CH4 over Co-ZSM-5. In the presence of O2, NO2 is formed via the oxidation of NO. Adsorbed NO2 then reacts with CH4. Nitrile species are observed and found to react very rapidly with NO2, and at a somewhat slower rate with NO and O2. The dynamics of the disappearance of CN species suggests that they are reactive intermediates, and that N2 and CO2 are produced by the reaction of CN species with NO2. While isocyanate species are also observed, these species are associated with A1 atoms in the zeolite lattice and do not act as reaction intermediates. A mechanism for NO reduction is proposed that explains why O2 facilitates the reduction of NO by CH4, and why NO facilitates the oxidation of CH4 by O2. 

The proposed mechanism is attractive in that it explains not only the manner in which NO2 initiates the reaction of CH4, but also the pathway to CO2 and N2. This mechanism would also explain why NO facilitates the combustion of CH4 by O2 [13, 18]. TPD experiments conducted in our laboratory have shown that Co-21SM-5 will not adsorb O2, whereas it will adsorb NO2. If the product of the reaction of CH4 with NO 2 is retained as an adsorbed species, then it is easy to see how NO2 (derived from the oxidation of NO) could facilitate the oxidation of CH4 by O2. 

In situ infrared observations show that the primary species present during the reduction of NO by CH4 over Co-ZSM-5 are adsorbed NO 2 and CN. When O2 is present in the feed NO2 is formed by the homogeneous and catalyzed oxidation of NO. In the absence of O2, NO2 is presumed to be formed via the reaction 3 NO = NO2 + N2O. The CN species observed are produced via the reaction of methane with adsorbed NO2, and transient response studies suggest that CN species are precursors to N2 and CO2. A mechanism for the SCR of NO is proposed (see Figure 10). This mechanism explains the means by which NO2 is formed from adsorbed NO and the subsequent reaction sequence by which adsorbed NO2 reacts with CH4 and O2 to form CN species. N2 and CO or CO2 are believed to form via the reaction of CN with NO or NO2. CH3NO is presumed to be formed as a product of the reaction of CH4 with adsorbed NO2. The proposed mechanism explains the role of O2 in facilitating the reduction of NO by CH4 and the role of NO in facilitating the oxidation of CH4 by O2. 

The activities of the catalysts for the oxidation of NO to NO2 and reduction of NOj by propene were measured, and compared with NO reduction under similar conditions The results are shown in Table 2. For all catalysts, the activities of the catalysts for NO oxidation were low, compared with NO or NOj reduction. For catalysts in groups A and B, NOj reduction was much ster than NO reduction of NO, and the C.F. s were much higher. 

Excess air is supplied to the oxidiser to keep the ammonia concentration below the explosive limit (see Chapter 9), reported to be 12 to 13 per cent (Chilton), and to provide oxygen for the oxidation of NO to NO2. 

The areas I and II in Figure 2.9 correspond to oxidation of NO ligand and shrinking (I) or minute elongation (II) of the intemuclear distance. There are only two cations... 

The interaction of NO, N20, and N02 reactants with the secondary copper-oxo sites leads to terminal 02, restoring the initial active sites (Figure 2.26). The central N02 semi-product is produced through oxidation of NO on the 3CuO Z centers, similarly to the nickel complexes described in Section 6.2.1. 

A function 1 has also to turn over simultaneously with functions 2 and 3, as it has to provide N02 to function 2. The oxidation of NO to N02 is therefore the first function of any efficient catalyst. 

Figure 5.1 shows that function 1 is therefore the oxidation of NO to N02, this last one being subsequently delivered to function 2 to oxidize HC to CxHyOz which will be delivered to function 3 to scavenge the adsorbed oxygen species left by the (NO)2 -adsorbed dinitrosyl species - decomposition. 

Figure 5.12. Catalytic oxidation of NO to N02 over 0.5, 1, 2wt.% Co/A1203. Successive isotherms. 200ppm NO/9vol.% 02/Ar total flow rate 250 cm3 min catalyst weight 0.2 g VVH 50 000 IT1 [26],...

Function 1, oxidation of NO to NOz, can be studied separately [3926] and its temperature of activation is adjusted to the temperature at which function 3 is working. (It does not mean that the amount of N02, at the outlet of the reactor, will be the same in the presence of a reductant, as there is a consumption of N02 during the interaction... 

The NOx storage was investigated at first. The collected results showed that a dual pathway is operating when starting from N0/02 mixtures the first route implies the well-known oxidation of NO to N02, and its subsequent adsorption via disproportionation to form nitrates (nitrate route), whereas the second novel route consists of a stepwise oxidation of NO in the presence of oxygen to form nitrite ad-species, which are progressively oxidized to nitrates (nitrite route). 

Figure 6.4c showed the storage uptake behaviour by using N0/02 over the reference Pi-lia/y-AEOj sample. Upon admission of NO (at = 0 s) both the NO and N02 outlet concentrations show a significant delay. Then the NO concentration increases, followed by that of N02. N02 formation is ascribed to the oxidation of NO by 02 according to the stoichiometry of reaction (2) ... 

The role of the Pt-Ba interaction in the mechanism of adsorption of NO species was also studied by a kinetic model reported in the literature [16]. The model, which consists of 10 elementary reversible steps, is based on the oxidation of NO to N02 over Pt and on the storage of N02 over Ba, and it was used to simulate the data collected over both the physical mixture and the ternary Pt-Ba/y-Al203 1/20/100 w/w sample. A spillover reaction between Pt and Ba oxide sites has also been included in the model to account for the observed lower thermal stability of Ba-nitrates in the presence of Pt [16]. Essentially, the model assumes that the adsorption of NO proceeds through the nitrate route and does not consider the nitrite route. 

The simulations [30] showed that the model satisfactorily reproduced the results collected over the physical mixture upon NO step addition in the presence of oxygen. Both the oxidation of NO to N02 and the dead time for the breakthrough of NO are reasonably simulated by the model, as indeed expected according to nitrate route adsorption. 

In the case of the Pt-Ba/alumina ternary sample, the dead time in the NO breakthrough upon a step change of NO in the presence of oxygen is reasonably well predicted by the model but the oxidation of NO to N02 is markedly overestimated. If the Pt dispersion in the model is lowered, the oxidation of NO to N02 is properly described but the NO breakthrough is no longer predicted. Therefore, the literature model is not able to describe at the same time the oxidation of NO to NO, and the NO breakthrough. 

To have a mixture N0 + N02 at the SCR catalyst intake, the presence of a DOC upstream of the system is required (oxidation of NO into N02). The DOC must be sized according to the optimal ratio NO/N02 = 1. 

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