The formation of N2 and

Ilchenko et al. [161—163] compared the oxides of Mn, Co, Cu, Fe and V, and found that Mn02 gives a selectivity to N20 of 42% at 155°C and Pnh3 = 0.1 atm at contact times, r, of 1.5—4 sec. Co304 produces less N20 and more nitrogen at 143°C (selectivity = 18% at Pnh3 = 0.2 atm, r = 5—15 sec). At these low temperatures, the selectivity to N20 was not very sensitive to variations in r, suggesting that the products are formed by parallel reactions, viz. 

In principle, nitrogen can also be formed by the catalyzed reaction with ammonia. 

The general rate equation for the oxidation of ammonia to nitrogen is of the redox type (161—163). 

Rate coefficients (molecule cm-2 sec-1 atm-1) and activation energies (kcal mol-1) of ammonia to nitrogen 

Another copper catalyst, prepared by treating a NaY zeolite with copper nitrate, for ammonia oxidation (160—185°C) has been studied by Williamson et al. [349], The reaction is first order in NH3 and zero order in oxygen. The mechanism here is based on a Cu(II)(NH3)4+ complex formed in the large cavities of the zeolite. The rate-determining step is the reduction of Cu(II) by ammonia. 

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Figure 10.2. Operando spectroscopic investigation of the NO transformation on Rh/Al203. (a) IR spectra recorded after successive NO pulses at 300°C on a prereduced catalyst, (b) and (c) Changes in the intensity of IR bands related to the adsorbates during successive NO pulses on a CO preadsorbed surface at 300°C and correlative changes in the formation of N2 and N20, respectively (reproduced with permission from Ref. [42]).

In summary, a complex chemistry could be envisaged for explaining the formation of N2 and N20 under lean conditions. In the particular case of N20, nitrosyl, dinitrosyl species as well as nitrates and nitrites species could be considered as intermediates particularly under lean conditions. 

Transient response experiments have revealed that the formation of N2 and N2O during NO reduction by H2 over Rh proceeds without the intervention of H2 By contrast, the formation of NH3 and H2O involves the reactions of dissociatively chemisorbed H2 with N and 0 atoms, respectively. The results obtained from experiments involving the reduction of adsorbed NO and isotopic substitution of NO for NO can be interpreted on the basis of the reaction mechanism presented in Fig. 11. Key elements of this mechanism are that NO is adsorbed reversibly into a molecular state, that reduction is initiated by the dissociation of molecularly adsorbed NO, and that all products are formed via Langmuir-Hinshelwood process. 

Similar arguments can be applied for the formation of N2 and its oxides. Enthalpies of decomposition, which are estimated on the basis of the products described above, usually result in a conservative prediction. In practice, decomposition is nearly always incomplete due to the evaporation of volatile reaction products and polymerization or tar formation by heavier molecules. 

Figure 34 shows the NO and propylene conversions as fimctions of temperature in the case of Cu-Al-MCM-41-10-61 (Si/Al = 10 Cu exehange 61%). The maximum conversions observed for the formation of N2 and of NO2 are around 370 and 450 °C, respectively. The latter product appears only at temperatures higher than 370 °C. Propylene is essentially oxidized to carbon dioxide and water. 

The following main reactions can be invoked to explain the formation of N2 and NH3 ... 

As shown in Figure 9, UV-irradiation of Mo-MCM-41 in the presence of a mixture of NO and CO leads to the formation of N2 and C02 with a linear dependence on UV-irradiation time, whereas the turnover frequency exceeds 1.0 after 2h (Tsumura et al., 2000). After 3h, NO conversion and selectivity towards N2 are close to 100%, with only a small amount of N20 formed. Figure 10 shows that there is a good correspondence between the yield of N2 produced and the yield of PL of tetrahedral molybdenum species and the amount of Mo4+ ions generated upon... 

As shown in Fig. 45, UV irradiation of the copper(l) ion species anchored ZSM-5 zeolite in the presence of NO at 275 K leads to the formation of N2 and O2 with a good linear relationship between the UV irradiation time and the conversion of NO as well as a good stoichiometry during the long UV irradiation period (172-180). 

TPSR experiments were performed to investigate the reactivity of preadsorbed ammonia with gaseous NO, both in the absence (Fig. 4) and in the presence of gaseous oxygen (Fig. 5). The figures show the consumption profile measured when NO is fed over the NH3 preadsorbed WT, WA, WIOTA and W13TA catalysts. The figures also show the formation of N2 and the ammonia profile, which was completely consumed in all the experiments. 

The kinetics of NOx reduction were found to be very similar to those of C3H6 oxidation both reactions are 1.8 order in O2, zero order in C3H6 and inhibited by NO (Fig. 1-5). This is consistent with NOx reduction occurring via the dissociation of molecularly adsorbed NO on vacant Pt sites, followed by the formation of N2 and N2O by the combination of adsorbed N and NO. This mechanism is supported by our earlier TAP study [6]. It is also in agreement with the observation that the ratio of N2 N2O formed is independent of contact time (Fig. 2) indicating that N2 and N2O are formed from parallel routes. This can be represented as ... 

In blank tests, silicious MCM-41 or bulk M0O3 did not exhibit photocatalytic reactivities in the presence of a mixture of NO and CO under UV-irradiation. The photocatalytic decomposition reactions of NO in the absence and presence of CO were performed on Mo-MCM-41 mesoporous molecular sieves. UV-irradiation of the Mo-MCM-41 in the presence of NO led to the evolution of N2 as well as N2O and N02- Moreover, it was found that the photocatalytic decomposition reactions of NO was dramatically enhanced by the coexistence of CO, leading to the formation of N2 and CO2. UV-irradiation of Mo-MCM-41 in the presence of a mixture of NO and CO leads to the formation of N2 and CO2 with a good linearity against the UV-irradiation time, while the turnover number (TON), (defined as the value of the number of photo-formed N2 molecules divided by the total number of Mo species in the catalyst) exceeded unity after irradiation for 2 h, as shown in Fig 5. These results clearly indicate that the reaction proceeds photocatalytically [6]. 

Fig. 1 shows that the formation of N2 and, consequently, the total NO consumption increase with increasing temperature, reaching a maximum value at about 475°C. The... 

Since Aff° is negative, raising the temperature will decrease Kp, thereby increasing the amount of reactants and decreasing the amount of products. No, the formation of N2 and CO2 is not favored by raising the temperature. 

The experiments were made with ammonia using an all-glass ozonizer the surface of the inner electrode of which was deposited with a thin film of a metal. The metals used were Pt, Pd, Ni, Au and Ag. With recirculation of the gas mixture at a pressure close to atmospheric steady-state conversions into hydrazine as high as 13.5% were attained with Pd which is an increase in the N2H4 yield by a factor of 4 (Fig. 18). The overall conversion of ammonia and the formation of N2 and H2 were almost independent of the metal coatings (Fig. 18) suggesting that hydrazine is not an intermediate in the d omposition of NH3 into Nj and Hj. Therefore, it seems that there are two independent reaction pathways the formation of hydrazine which is a surface reaction that is dependent on the state of the electrode surface... 

FIGURES.6. Catal) ic oxidation ofNHs on a Ru02(1 10) surface [34], (a) Steady-state rates of N2 and NO formation as a function of O2 partial pressure with fixed T and Pnhs (b) Respective selectivities for the formation of N2 and NO. 

Carbonaceous material was deposited on the catalyst surface simultaneously (6) with the formation of N2 and COx in Reaction A (Figure 2). After a mixture of NO and O2 was introduced( Reaction B ), COx was produced simultaneously with the formation of N2. However, the formation of N2 decreased gradually and completely terminated after 60 min with no more formation of CO. From these results, it is suggested that carbonaceous material deposited on the catalyst surface plays an important role in this reaction and that the ftrst step of the reaction is the adsorption of C3H6 on the catalyst surface. 

Although the reaction pathway for the formation of N2 and CO2 has been elucidated, the type of adsorbed NO and CO involved in the reaction remains unknown. The types of CO and NO adsorbed on Rh are closely related to the surface state of Rh and the partial pressure of NO and CO (5-72). An investigation of how the various types of adsorbed CO and NO interact and react may provide some insight into the nature of Rh sites that are active for the NO and CO reaction. 

Under suitable conditions, these gases can be made to react to form nitrogen (N2) and the less harmful carbon dioxide (CO2). (a) Write an equation for this reaction, (b) Identify the oxidizing and reducing agents, (c) Calculate the Kp for the reaction at 25°C. (d) Under normal atmosphalc conditions, the partial pressures are = 0.80 atm, Pco, = 3.0 X 10 atm, Pco = 5.0 X 10 atm, and P o = 5.0 X 10 atm. Calculate Qp and predict the direction toward which the reaction will proceed, (e) Will raising the temperature favor the formation of N2 and CO2 ... 

According to Sample Exercise 15.7, Kg = 2.79 X 10 at this temperature. Therefore, the quotient PNH3/PN2PH2 will need to decrease from 1.34 X 10 to 2.79 X 10 for the system to achieve equilibrium. This change can happen only if Ihe partial pressure of NH3 decreases and those of N2 and H2 increase. Thus, Ihe reaction proceeds toward equilibrium via the formation of N2 and H2 from NH3 that is, the reaction proceeds from right to left. 

X 10 atm. Calculate Qp, and predict the direction toward which the reaction will proceed, (e) Will raising the temperature favor the formation of N2 and CO2 ... 

Ammonia is stable under SCWO conditions without a catalyst up to 600°C. Degradation leads to the formation of N2 and N2O. The destruction efficiency at 530-700°C and 246 bar with a catalyst reaches more than 90%. Although the available solid surface increases by a factor of 30, the reaction rate increases only by a factor of 4. Thus, the reaction is mainly homogeneous. Application of a Mn02/CeO... 

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