Reduction of NO to

Chemical reduction. The injection of ammonia reduces NO emissions by the reduction of NO , to nitrogen and water. Although it can be used at higher temperatures without a catalyst, the most commonly used method injects the ammonia into the flue gas upstream of a catalyst bed (typically vanadium and/or tin on a silica support). 

Three-way catalysts (TWC), or equilibrium catalysts are designed for the simultaneous control of three automotive pollutants NO, CO, and hydrocarbons (HC). Since rhodium has the desired selectivity for the reduction of NO to with minimum NH-j formation and is also selective... 

Additional experiments were performed to quantify the effect of varying the Mo/Pt ratio on the selectivity for reduction of NO to (or... 

The high yields on the lean side of stoichiometric pose a dilemma. It is desirable to operate lean to reduce hydrocarbon and carbon monoxide emissions but with fuel containing bound nitrogen, high NO yields would be obtained. The reason for the superequilibrium yields is that the reactions leading to the reduction of NO to its equilibrium concentration, namely,... 

Furusawa, T Seshan, K Lercher, JA Lefferts, L Aika, K. Selective reduction of NO to N2 in the presence of oxygen over supported silver catalysts, Appl Catal, B Environmental, 2002, Volume 37, Issue 3, 205-216. 

Similar to the situation with nitrate esters, the two-stage gas-phase reaction resulting from the combustion of ADN occurs due to the reduction of NO to N2, which is reported to be a termolecular reaction. The heat flux transferred back from the preparation zone to the melt layer zone dominates the gasification process occurring in the melt layer zone. 

The third chemical equation, involving nitric oxide, represents a termolecular reaction. Therefore, the overall order of the reaction is expected to exceed that of the second-order reaction generally assumed in the pre-mixed gas burning model. The high exothermicity accompanying the reduction of NO to N2 is responsible for the appearance of the luminous flame in the combustion of a double-base propellant, and hence the flame disappears when insufScient heat is produced in this way, i. e., during fizz burning. 

The results indicate that the reduction of NO to N2 is inhibited by the reduced temperature in the gas phase on the addition of lead tetramethyl. In addition, the same authors examined the effect of alkyl radicals on the flame speed by using different kinds of metal alkyls. They found the flame speed not to be affected by... 

Metallic nickel is known to catalyze the reduchon of NO in its reachons with aldehydes or hydrocarbon gases, and the primary reachon in the dark zone of a double-base propellant is the reduction of NO to N2. Small amounts of fine Ni particles or organic nickel compounds are incorporated into double-base propellants to increase the reaction rate in the dark zone. 

However, the luminous flame front rapidly approaches the burning surface when the pressure is increased. This reaction is also caused by the reduction of NO to N2, as in the reaction process of double-base propellants. 

The results indicate that the basic chemical reaction mechanism in the gas phase, which involves the reduction of NO to Nj, remains unchanged by the addi-... 

Recent automobile exhaust emissions standards are summarized in Table III, and a review of the catalytic systems designed to meet these standards has recently appeared (26). Catalytic converters have been used as a part of emission control systems since 1975. One approach has been to use a dual bed catalytic converter where the reduction of NO to N2 occurs over the first bed, and excess O2 is provided to the second bed to oxidize the CO and hydrocarbons more completely. Typically, the exhaust contains compounds listed in Table IV plus some poisons containing Pb, P, S etc, (27). The catalytic system must reduce concentrations of CO, hydrocarbon and NOx to legally acceptable levels. 

The electrochemical reduction of nitric oxide in solid-state electrochemical cell is an interesting field surveyed in [95]. The working principle of the cells is the cathodic reduction of NO to nitrogen and oxygen anions. In [95], the properties of various types of solid-state electrochemical cells used for NO reduction are presented and discussed. It is shown that the cathode materials with a high redox capacity and oxygen vacancies are most active for the electrochemical reduction of nitric oxide, whereas noble metal-based electrodes show a much lower selectivity. As an alternative route, the promotion of the reduction with a reductive agent is also considered. 

The heats of explosion, of the pyrolants are shown as a function of pressure in Fig. 12.3. It is evident that H p of the NP pyrolant is increased by the addition of nickel particles in the low-pressure region below about 2 MPa. The measured of the NP-Ni pyrolant becomes less pressure-dependent and reaches approximately 97 % of the theoretical value. The results indicate that the lower value of H p of the NP pyrolant is caused by incomplete combustion at about 4 MPa and that the increased H p of the NP-Ni pyrolant is caused by a catalytic effect on the gas-phase reaction which increases the temperature. The gas-phase reduction of NO to N2 in the dark zone of the NP pyrolant in the low-pressure region is promoted by the addition of the nickel particles. 

The formation of azomethane as a two-electron oxidation product of l,2-Me2Hz, and the exclusive label on 15NH3 suggest that the full six-electron reduction of NO+ to NH3 is accomplished through three successive two-electron processes. The plausible intermediates must be [Fen(CN)515HNO]3- and [Fen(CN)515NH2OH]3-. The proposed mechanism involves an initial adduct formation, similar as for other hydrazines (the DFT calculations show that the adduct formation is not sterically hindered), as shown by Eq. (16), followed by a two-electron transfer from l,2-Me2Hz to the N-atom in nitrosyl, Eq. (17). 

These porous solids obviously have very high surface areas, and they lend themselves naturally to service in catalysis. Palladium catalysts supported on alumina aerogels have been used successfully to remove CO and NO from automobile exhausts,13 and a V205/Ti02 aerogel is itself a catalyst for the selective reduction of NO to N2 and water by gaseous ammonia.14... 

Electrophilic attack by H+ on bent nitrosyl ligands leads to reduction (190, 205, 216). Complexes containing HNO, NHOH, and NH2OH have all been prepared in this manner, raising the possibility, as yet unrealized, of a catalytic reduction of NO to hydroxylamine. The simplest and best characterized of these reactions is (91) reported by Enemark et al. (205). 

Several processes appear to account for the reduction of NO to N20. This reaction proceeds slowly in the presence of either Pd(0) or Cu(I) alone, but is much faster when both metals are present, leading the authors (189) to propose a Pd(II)-Cu(I) chloride-bridged species as the most active reductant. Significantly, N20 and C02 are produced in 1 1 proportions when CuCl is used in place of CuCl2, and the rate of the reaction increases as the initial concentration of CuCl is increased from 10"3 to 1.0 M. 

With increasing pressure, CO increases relative to C02 and NO is reduced to N2. Dissolved w-vapor or pretreatment with NOz have no measureable effect on the combustion chemistry, but small amounts of 02 catalyze the oxidation of CO to C02, and the reduction of NO to N2... 

Since the reaction N20 + Na = N2 + NaO is known to be rapid the injection of NaN3 into hot exhaust gas might allow the rapid and selective reduction of NO to N2 The author has done a preliminary experiment in which NaN3 decomposition was found to rapidly and selectively reduce NO, but the cost of NaN3 and the handling difficulties it involves make this observation more a matter of scientific interest than of potential practical utility. 

The cycle of Scheme 27 demonstrates that the [3 H+/3 e ] reduction of NO to give NH2OH can be separated into two distinct steps A [2 H+/2 e ] reduction that involves no Mo electrons, and a [1 H+/l e ] reduction in which one electron comes from the Mo center. Note that the [2 H+/2 e reduction step takes place first thereby skipping the N° oxidation state with formation of thermodynamically favored dinitrogen. 

In strongly acidic media nitrous acid is in equilibrium with NO+, and one pathway for reduction of nitrous acid is reduction of NO+ to NO. Likewise, NO is oxidized via NO+ in certain cases (252). The calculated potential of the NO+/NO couple is dependent on AfG° of HNOz and the equilibrium constant for production of NO+ both of these parameters are somewhat uncertain. An early value of 1.45 V was reported in an electrochemical study of the NO/HNOz equilibrium (266) an assumed value for the formation constant of NO+ was employed. A value of 1.21 V can be calculated from the substantially revised thermodynamic parameters selected by Ram and Stanbury (252). This latter value is preferred because of the numerous cross-checks described in the paper. 

Reduction of NO to N20 or N2 is important in biological denitrification where anaerobic organisms are involved and model studies using copper catalysts have been studied.42 Much study on other catalytic reductions of NO (and of N02) has been made in connection with atmospheric pollution.43... 

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