N2O decomposition

The decomposition of nitrous oxide (NjO) to nitrogen and oxygen is preformed in a 5.0 1 batch reactor at a constant temperature of 1,015 K, beginning with pure NjO at several initial pressures. The reactor pressure P(t) is monitored, and the times (tj/2) required to achieve 50% conversion of N2O are noted in Table 3-19. Use these results to verify that the N2O decomposition reaction is second order and determine the value of k at T = 1,015 K. 

As we will see shortly, the rate expression can take various forms, depending on the nature of the reaction. It can be quite simple, as in the N2Os decomposition, or exceedingly complex. 

Contacting the synthesized zeoHte with the reagent leads to a ready-to-use catalyst. No further pretreatment before reaction is needed. The performance of such a novel one-pot catalyst was tested in N2O decomposition, and was found to be even superior to the conventionally prepared counterpart This was ascribed to the minimization of FeO,c formation. 

It is concluded that zeoHte beta can be simultaneously detemplated and Fe-exchanged without FeO formation by treating the parent zeoHte with a Fenton reagent. The catalyst shows good performance on N2O decomposition. This one-pot process simplifies its preparation protocol and can be extended to other systems. Indeed, our approach was followed by Liu et al. [170], for preparing Fe-S BA-15 for benzylation of benzene with interesting results. 

NO and N2O decomposition show large differences between metals with both rates being higher on Pt at low temperatures and higher on Rh at high temperatures. NO decomposition is also found to be more strongly inhibited by O2 than N2O decomposition, and this inhibition is stronger on Rh. 

One-step hydroxylation of aromatic nucleus with nitrous oxide (N2O) is among recently discovered organic reactions. A high eflSciency of FeZSM-5 zeolites in this reaction relates to a pronounced biomimetic-type activity of iron complexes stabilized in ZSM-5 matrix. N2O decomposition on these complexes produces particular atomic oj gen form (a-oxygen), whose chemistry is similar to that performed by the active oxygen of enzyme monooxygenases. Room temperature oxidation reactions of a-oxygen as well as the data on the kinetic isotope effect and Moessbauer spectroscopy show FeZSM-5 zeolite to be a successfiil biomimetic model. 

This discovery was quite unexpected, since iron oxide has been never reported as an active catalyst in either partial or full oxidation. The studies of two simplest reactions, i.e. O2 isotopic exchange and N2O decomposition, revealed a dramatic change of Fe properties in the ZSM-5 matrix compared to Fe203 [4]. Fe atoms lose their ability to activate O2 but gain remarkably in their ability to activate N2O. It gives rise to a great effect of the oxidant nature in the reaction of benzene oxidation over the FeZSM-5 zeolite (Table 1). Thus, in the presence of N2O benzene conversion is 27% at 623 K, while in the presence of O2 it is only 0.3% at 773 K. And what is more, there is a perfect change of the reaction route. Instead of selective phenol formation with... 

Figure 2. Kinetics of N2O decomposition at 523 K followed by a-oxygen loading on FeZSM-5 zeolite surface.

For this purpose we studied a temperature-programmed interaction of CH with a-oxygen. Experiments were carried out in a static setup with FeZSM-5 zeolite catalyst containing 0.80 wt % Fe203. The setup was equipped with an on-line mass-spectrometer and a microreactor which can be easily isolated from the rest part of the reaction volume. The sample pretreatment procedure was as follows. After heating in dioxygen at 823 K FeZSM-5 cooled down to 523 K. At this temperature, N2O decomposition was performed at 108 Pa to provide the a-oxygen deposition on the surface. After evacuation, the reactor was cooled down to the room temperature, and CH4 was fed into the reaction volume at 108 Pa. 

Comparative kinetic and in-situ DRIFT studies of the N2O decomposition over Co-, Fe- and Cu-ZSM-5 have been performed. The implications of the presence of O2, CO, NO, H2O and SO2 on the catalyst activity and stabilitiy and on the mechanism are evaluated. 

Experimental setup and procedures. The experimental setup for N2O decomposition consisted of a gas mixing section, a reactor and a gas analysis section. A quartz fixed bed reactor of 5 mm I.D. was used, containing 20 mg of catalyst (106-212 mm) diluted with... 

The SiC diluent did not contribute to the N2O decomposition at the reaction temperatures studied. Prior to each run, the catalyst was subjected to calcination by heating the catalyst in He at 30 K/min to 923 K and maintaining this temperature for one hour. Subsequently, the temperature was decreased to the desired value and the feed mixture was passed over the bed. Temperature and feed composition were varied in a random order in the experiments. Generally, 40 to 50 min after a change of conditions the conversion levels were constant and considered as the steady-state. At least five analyses were averaged for a data point. 

Water exerts both a deactivating and inhibiting influence on Cu and Fe samples, while the reaction over Co is only inhibited. The deactivation of Fe- and Cu-ZSM-5 is clearly due to migration and the sintering of the active component in H2O atmospheres [34]. The Co-ZSM-5 catalyst is much more hydrotheimally stable in wet gas conditions [34,35]. The inhibition by water can be accounted for in a similar way as for CO via competitive adsorption on active sites, like in selective NO reduction studies [34]. For N2O decomposition this yields an expression like eq. (12). At 793 K Kn amounts to about 0.7 kPa". ... 

Since the insulator oxides such as MgO, CaO and AI2O3 are involved in this branch, it would be worth examining whether the mechanism of N2O decomposition on these insulator oxides is different from that on p-type oxides. 

The addition of nitric oxide markedly increases280 the rate of N2Os decomposition. In terms of the accepted mechanism, NO removes NOa in the very rapid reaction (29), thereby preventing reassociation. The stoichiometric equation is now... 

RATE COEFFICIENTS FOR ELEMENTARY REACTIONS IN N2Os DECOMPOSITION... 

RATE PARAMETERS FOR N2Os DECOMPOSITION IN VARIOUS SOLVENTS... 

Correlations between catalytic activity and a variety of bulk properties of semiconductors have been reported (i) the average band gap of III-V and II-VI semiconductors and activity towards hydrogenation of isopropanol (ii) enthalpy of oxides and their activity towards oxidation of propylene and (iii) number of d-electrons (and crystal field stabilization energy) or 3rf-metal oxides and their activity towards N2O decomposition. The last correlation, due to Dowden (1972), is important since it provides a connection between heterogeneous catalysis and coordination chemistry of transition-metal compounds. A correlation between the catalytic activity of transition-metal sulphides towards hydrodesulphurization of aromatic compounds and the position of the transition metal in the periodic table has been made by Whittingham ... 

This mechanism requires binding of metal electrons to the chemisorbed molecule without formation of a chemical bond (oxidation). The work function of the metal must be of medium height if the most favorable activation of the N2O decomposition is desired. The energy of activation on gold ( = 4.71 volts) is 29.0 kcal, but on platinum ( = 5.36 volts) 32.5 kcal., according to Hinshelwood and Prichard (69). The relative increase of the energy of activation (12.1%) from platinum to gold is about the same as that of the work function (13.8%). 

N2O decomposition on nickel increases suddenly at the Curie point, owing to a smaller electronic interaction in accordance with the foregoing explanation. On the other hand, the electronic work function of nickel, according to Cardwell (71), above the Curie point is 0.2 volt higher than below it. The transfer of metal electrons to the N2O molecules, therefore, occurs less readily above the Curie point. Hence the bond between an 0 atom and N2 in the adsorbed N2O molecule is not weakened so much at temperatures above the Curie point. Thermal decomposition of N2O, therefore, requires a higher energy of activation. ... 

TPR, N2O decomposition, H2 adsorption, TPD experiments were done with a pulse chromatographic reactor. 

Dilute solutions (x <0.05) are particularly interesting since, in these solids, M cations can be considered as virtually isolated in the AO matrix, and mutual M M interactions are absent. Therefore, the intrinsic catalytic behavior of isolated centers M can be signled out (25). The catalytic behavior can be compared for M in matrices of the same symmetry but different ionicity (e.g., AO = MgO, CaO, NiO, or SrO) or those also differing in symmetry (e.g., AO = NiO or ZnO). For example, it has been shown that the activity for N2O decomposition of both Ni2+ and Co2+ ions is lower when the ions are hosted in ZnO than in MgO (330). A progressive increase of x allows one to follow the insulator to semiconductor transition of the MxAi xO system in a controlled way without changing the local structure of M as surface active centers. 

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