Catalytic Decomposition Of Nitrous Oxide Research Articles

Stainless steel wire mesh-supported potassium-doped cobalt oxide catalysts for the catalytic decomposition of nitrous oxide

Structured catalysts consisting of potassium-doped cobalt oxide supported on stainless steel wire mesh were tested for the decomposition of N2O under dry and wet conditions. The cobalt oxide catalysts were prepared by the ammonia-evaporation-induced method. Of the several doping procedures tested, dropwise impregnation with potassium carbonate solutions provided the best catalytic results at lower K/Co molar ratios. Kinetic analysis of a potassium-doped catalyst yielded a reaction order on the N2O partial pressure slightly below unity (0.87). The activation energy values and the natural logarithms of the pre-exponentials factors for the different catalysts followed the classical compensation effect. This effect may be the result of a combination of competing reactions on different groups of active centers. Thus, cobalt ions affected by potassium display a low activation energy (∼40kJ/mol), whereas cobalt atoms unaffected by potassium display a higher activation energy equal to that of the undoped catalysts (∼106kJ/mol). The catalytic activity of the catalysts in N2O decomposition increases with the amount of reducible Co3+ ions, although there does not appear to be a direct relation between the amount of Co3+ ions and the textural and crystal properties of the catalysts. The addition of water produces some inhibition of the N2O decomposition reaction on K-doped catalysts, although catalytic activity is completely restored when the water is removed from the reaction stream. The catalysts prepared in this work were found to be among the most active, selective and stable catalysts reported in the literature.

Design and performance characterization of a sub-Newton N2O monopropellant thruster

This paper describes the research at Beihang University for developing a sub-Newton thruster based on catalytic decomposition of nitrous oxide (N2O) for fine attitude control of small spacecrafts. The characteristics of the N2O self-pressurization feeding process as well as the preheating process of a sub-Newton N2O thruster were studied. Experimental and simulated results indicated that the tank pressure decreases during the N2O self-pressurization process. The influence on the preheating process of the surface emissivity, the preheating power, the thickness of combustor chamber and the insulation material, were compared. N2O catalytic decomposition experiments were carried out to evaluate the reaction performance of Iridium impregnated modified alumina catalyst, such as activation temperature and reaction temperature. Successful activation and self-sustaining reaction were achieved at 523 K. It was found that the integral structure of the reactor and the loading factor of the catalyst-bed can influence the reaction effect. Based on further experiments looking for proper catalyst-bed, a thruster with a Φ10 mm×25 mm catalyst-bed was designed and fabricated. The vacuum performance of the thruster at different N2O flow rates was evaluated using a vacuum experimental system, which consists of a vacuum chamber and a sub-Newton-thrust measuring stand. Static vacuum thrusts ranging from around 140 mN to 970 mN were achieved with the flow rates altering from around 0.1 g/s to 0.6 g/s. The highest specific impulse reached 1640 N s/kg.

ChemInform Abstract: Catalytic Decomposition of Nitrous Oxide on “in situ” Generated Thermally Calcined Hydrotalcites.

Abstract Catalytic decomposition of nitrous oxide to nitrogen and oxygen has been carried out on “in situ” generated thermally calcined hydrotalcites of the general formula MAlCO3HT, where M stand for Ni, Co and Cu, in the temperature range 140–310°C at 50 Torr (1 Torr=133.3 Pa) initial pressure of the gas. All the catalysts showed first-order dependence on nitrous oxide without any inhibition by oxygen. Among the catalysts studied, NiAlCO3HT was the most active, followed by the cobalt and copper catalysts. These catalysts are more active in comparison with earlier reported Cu-ZSM-5, Co-ZSM-5 and Rh-ZSM-5 catalysts based on their conversion for the decomposition. The enhanced activity can be attributed to non-stoichiometry and dispersion of the active mixed metal oxides. Prior to the kinetic runs, the catalytic precursors were characterised by X-ray diffraction, thermogravimetry-differential scanning calorimetry measurements, IR, transmission electron microscopy and nitrogen adsorption measurements.

Catalytic decomposition of nitrous oxide over Fe-BEA zeolites: Essential components of iron active sites

The catalytic decomposition of N2O was investigated over Fe-BEA zeolites treated with various methods such as reduction, steaming and dissolution with potassium nitrate and nitric acid solutions in order to deduce the essen- tial components of the active sites for the decomposition. The iron species were characterized by XPS, XANES, ESR, NO adsorption, and linear sweep voltammetry. The reduction-treated Fe-BEA zeolite with the large amounts of Fe(II) and Fe(III) species showed the highest activity. On the contrary, the dissolution treatment with the potassium nitrate solution seriously deteriorated the catalytic activity of the Fe-BEA zeolite by agglomerating iron oxide clusters and interaction between iron and potassium atoms. The catalytic roles of Fe(II)/Fe(III) species and the negative effect of potassium on the catalytic activity of the Fe-BEA zeolites were discussed.

Pulse Transient Responses of NO Decomposition and Reduction with H2on Ag−Pd/Al2O3

Catalytic decomposition of nitric oxide (NO) over Pd/Al2O3 and Ag−Pd/Al2O3 has been studied using the pulse transient response technique coupled with in situ infrared (IR) and mass spectrometry (MS) at 723−823 K. In the absence of H2, pulsing NO over the Pd/Al2O3 catalyst produces adsorbed NO species (i.e., Pd+−NO, Pd0−NO, and Pd−NO−) as well as gaseous N2, O2, and N2O products. Transient responses of the N2 and O2 profiles show that the addition of Ag onto Pd/Al2O3 catalyst shifts the O2 profile forward, increases oxygen formation and the oxidation resistance of Pd, but did not decrease the amount of retained oxygen (Oret) and did not improve the catalytic cycle for NO decomposition. Oret on the Pd surface is not able to desorb in the temperature range of this study; however, Oret on Ag−Pd/Al2O3 can be desorbed at higher temperatures than its formation and adsorption temperature. The presence of H2 during the NO pulse allowed NO reduction to occur, producing N2, N2O, O2, NH3, and H2O. Pd/Al2O3 is a more ...

Fe-mordenite/cordierite monolith for the catalytic decomposition of nitrous oxide

Mordenite zeolites were coated on cordierite support by in situ hydrothermal method or dip-coating method. The mordenite/cordierite was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques and their stability was studied. The mordenite/cordierite monolith prepared by in situ synthesis showed much better stability than that prepared by dip-coating. Iron was introduced into mordenite/cordierite by ion exchange and Fe-mordenite/cordierite catalyst was prepared. Fe-mordenite/cordierite prepared from in situ synthesis exhibited good activity and stability for N 2O catalytic decomposition, with great potential for future application.

Experimental research on catalytic decomposition of nitrous oxide on supported catalysts

A series of Ni–Co catalysts were prepared in this study. Experimental results showed that supported Ni–Co catalyst had the ability of decomposition of N 2O, and its activity was increased with increasing content of the catalytic components on the support. Study indicated that a little addition of platinum catalytic component to the Ni–Co catalyst would benefit on improving its activity, and it was obvious under lower reaction temperature. Experimental results showed that the Pt–Ni–Co catalyst had good stability. XRD, SEM, TG and ICP characterization also showed that the prepared catalyst had a good stable structure before and after reaction.

Influence of microwave irradiation on catalytic decomposition of nitrous oxide over Rh/Al2O3 catalyst

Abstract Alumina-supported Rh catalysts were prepared by deposition–precipitation (DP) and impregnation (IMP) methods adopting conventional heating (CH) and microwave irradiation (MW), characterized by temperature programmed reduction (TPR), X-ray diffraction, XRD, CO-diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) techniques and evaluated for their activity in N 2 O decomposition. The activity of the DP catalyst was found to be significantly higher than the IMP catalyst, which was manifested in the formation of electron deficient Rh species, as observed by CO-DRIFTS analysis. MW irradiation further enhanced the number of the Rh active sites. A combination of DP and MW irradiation produced a catalyst with a superior activity than that prepared by either of the methods.

Kinetic Oscillations During the Catalytic Decomposition of Nitrous Oxide

AbstractFor Abstract see ChemInform Abstract in Full Text.

Kinetic oscillations during the catalytic decomposition of nitrous oxide

This review summarises experimental and modelling studies concerning the development of kinetic oscillations during the catalytic decomposition of nitrous oxide. Oscillations over Cu-ZSM-5 catalysts have been investigated using several methods and it could be shown that the formation of a strongly adsorbed nitrate formed in side reactions and the interaction of this species with atomic oxygen is responsible for the development of kinetic oscillations. The reaction of nitrous oxide over Fe-ZSM-5 catalysts shows similarities to the observations made with Cu-ZSM-5, but kinetic oscillations occur only in the presence of water vapour. On the other hand, isothermal oscillations observed over precious metal catalysts can be explained by an oxidation/reduction mechanism including the restructuring of the active catalyst surface under reaction conditions.

Catalytic decomposition of nitrous oxide over catalysts prepared from Co/Mg-Mn/Al hydrotalcite-like compounds

Co/Mg-Mn/Al hydrotalcite-like compounds with Co:Mg:Mn:Al molar ratios of 4:0:2:0, 2:2:2:0, 2:2:1:1, 4:0:1:1, 4:0:0:2 and 2:2:0:2 were prepared by coprecipitation method. The mixed oxides obtained by calcination at 500°C were characterized using various techniques (XRD, IR, BET surface area measurements, TPD and TPR). The activities of calcined hydrotalcites were tested for N2O decomposition in an inert gas, and in the presence of oxygen and water vapor as well. Among the catalysts screened, the catalyst prepared from Co hydrotalcite containing Al and Mn as the trivalent cation showed the highest activity, which was retained in the presence of oxygen but was inhibited by water vapor. Redox properties of the catalysts play an important role in the reaction and optimum extent of reduction is necessary for achievement of the highest catalytic activity.

Pulsed ENDOR Study of Cu(I)−NO Adsorption Complexes in Cu−L Zeolite

The local environments of Cu(I)-NO adsorption complexes formed in zeolites Cu-L and Cu-ZSM-5 were studied by electron spin resonance (ESR), pulsed electron nuclear double resonance (ENDOR), and hyperfine sublevel correlation spectroscopy (HYSCORE). Cu(I)-NO complexes have attracted special interest because they are important intermediates in the catalytic decomposition of nitric oxide over copper exchanged zeolites. Recently, detailed structures of the complexes in Cu-ZSM-5 zeolites, O2-Al-O2-Cu(I)-NO, have been proposed on the basis of quantum chemical calculations (Pietrzyk, et al. J. Phys. Chem. B 2003, 107, 6105. Dedecek, et al. Phys. Chem. Chem. Phys. 2002, 4, 5406). 27Al pulsed ENDOR and HYSCORE experiments allowed the hyperfine coupling parameters of an aluminum nuclei found in the vicinity of the Cu(I)-NO complex formed in zeolite Cu-L to be estimated. The data indicate that the aluminum atom is located in the third coordination sphere of the adsorbed NO molecule in agreement with the suggested geometry of the adsorption sites. Broad distributions of aluminum nuclear quadrupole and hyperfine coupling parameters and short electron spin relaxation times of the Cu(I)-NO species prevented the determination of the 27Al hyperfine couplings for zeolite Cu-ZSM-5.

Analysis of N 2O decomposition over fixed bed mixed metal oxide catalysts made from hydrotalcite-type precursors

The kinetic modeling and analysis for the catalytic decomposition of nitrous oxide into nitrogen and oxygen have been performed based on some experiments over a fixed bed of mixed metal oxide catalysts made from calcined hydrotalcite-type precursors. The hydrotalcite-type compounds were obtained by co-precipitation of various metal nitrates with the addition of the precipitants and under controlled pH. The reactions were carried out under atmospheric pressure in the temperature range 250–500 °C and space velocities were set between 15,000 and 60,000 h −1. A reaction rate model derived from the mechanisms of adsorption and sequential decomposition of nitrous oxide has been applied to the decomposition operation of a fixed bed reactor. The mechanistic aspects of all the relevant reactions could be represented exactly for the operation range of temperature, concentration and parameters of reactor concern.

Bis(mu-oxo)dicopper as key intermediate in the catalytic decomposition of nitric oxide.

The direct decomposition of NO into N2 and O2 is the simplest and most desirable approach to NO abatement. Although no catalysts are known that fulfill all criteria required for application, some materials show a high NO conversion and could be potential catalysts in the near future. 2] The copper-loaded ZSM5 zeolite is the most studied catalyst with a high and stable NO decomposition activity. Since its discovery in 1986, considerable research efforts have been made in order to unravel the reaction mechanism and the active sites in Cu-ZSM-5. A growing consensus is found that a redox process cycling between Cu ions and Cu -ELO species is present (ELO extra lattice oxygen). 4±6] However, the nature of the Cu -ELO species has so far not unequivocally been identified. 4±7] Here, we report on the elucidation of this catalysis by identifying the bis( -oxo)dicopper species as the key intermediate that allows the smooth formation and desorption of O2. The detection of the bis( -oxo)dicopper species and its role was made possible by in situ spectroscopy, that is, under real reaction conditions. Firstly, UV/Vis monitoring of the catalyst using optical fiber technology was combined with on-line GC analysis. Secondly, direct structural information of the catalyst under working conditions was obtained with XAS (X-ray absorption spectroscopy). 11] So far, the bis( -oxo)dicopper core had only been characterized in homogeneous, synthetic complexes. Its isomerized ( 2 : -peroxo)dicopper core is present in natural actin membrane skeleton mesh. In addition, the raft may keep the Lck concentrations high at and near the TCR cluster. Lck may partition into the TCR-cluster raft and/or the rafts with Lck may coalesce with those containing the TCR cluster, which would raise the Lck concentration in the neighborhood of the TCR cluster. These possibilities are now under investigation in our laboratories.

Catalytic decomposition of N2O in medical operating rooms over Rh/Al2O3, Pd/Al2O3, and Pt/Al2O3

Catalytic decomposition of nitrous oxide (N2O) over alumina-supported rhodium, platinum and palladium has been investigated to purify the air contaminated with N2O in operating rooms. N2O decomposition activities over each catalyst in a mixture of 79% N2, 21% O2 and 60ppm N2O appear around 573K. These activities become higher with increasing temperature and finally reached almost 100% at 773K. Rhodium shows the highest N2O decomposition activity of almost 100% at 673K. When an organic anesthetic, a mixture of ethanol and isoflurane (CF3CHClOF2H), coexists at low concentrations with N2O, the activity on each catalyst decreases. However, rhodium shows the smallest deactivation. Among the tested catalysts, rhodium is the most suitable catalyst for decomposition of N2O in operating rooms.

The effect of NO x on the catalytic decomposition of nitrous oxide over Fe-MFI zeolites

This letter reports the effect of the presence of NO and NO 2 on the N 2O decomposition activity of Fe-MFI catalysts. In contrast to earlier studies it was shown that even traces of NO x are sufficient to cause a significant increase of the N 2O conversion. NO and NO 2 act as “co-catalysts” during N 2O decomposition by facilitating the desorption of strongly adsorbed atomic oxygen.

Kinetic Isotope Effects in the N2O Decomposition over NiO

The 15N and 18O kinetic isotope effects (KIEs) in the catalytic decomposition of nitrous oxide on NiO powder were determined in the temperature range of 625−825 K, and the following temperature dependencies were found: KIE(15N) = (0.821 ± 0.180) + (1445 ± 128)/T and KIE(18O) = (1.384 ± 0.124) + (1450 ± 89)/T. At initial pressures of N2O between 40 and 60 kPa, the reaction is first order in N2O and has an apparent activation energy of 131 ± 3 kJ mol-1. According to Bigeleisen's formalism, a bent, product-like NNO transition state and a fork-type NNOO transition state best fit the experimental results.

The Influence of Water Vapor and Sulfur Dioxide on the Catalytic Decomposition of Nitrous Oxide

In a catalysts screening for the nitrous oxide decomposition, three groups of catalysts (metals on supports, hydrotalcites, and perovskites) were studied relating to their activity in the presence of vapor or sulfur dioxide, in the temperature range from 200 to 500 °C. It was found that the water vapor strongly inhibates the nitrous oxide decomposition at T = 200-400 °C. The sulfur dioxide poisons the catalysts, in particular the perovskites. The catalysts Rh-ZrO 2 and Ex-Co, Rh-Al-HTlc are potentially suitable for the nitrous oxide decomposition in exhaust gas at around T = 500 °C.

Thermal Decomposition of N2O over ZnO: Kinetic Isotope Effects Study

The kinectic parameters were measured for the catalytic decomposition of nitrous oxide on ZnO powder between 40 and 60 kPa and the temperature range 725−835 K. Under studied conditions the reaction was found to be first order in N2O. An Arrhenius fit to the rate constants results in an apparent activation energy of 120 ± 4 kJ mol-1. Only the temperature-dependent nitrogen kinetic isotope effects were experimentally obtained, while the oxygen kinetic isotope effects were perturbed by 18O exchanged between N2O and ZnO. Theoretical interpretation of KIEs was evaluated according to Bigeleisen's formalism. From comparison of calculated results with the experimental data both a cis ONNO and a fork-type NNOO models are acceptable as transition state of the reaction.

Room A, 10/17/2000 9: 00 AM - 11: 00 AM (PS) Catalytic Decomposition of Nitrous Oxide

Room A, 10/17/2000 9: 00 AM - 11: 00 AM (PS) Catalytic Decomposition of Nitrous Oxide