Catalytic Decomposition Of N2O Research Articles

Influence of extra-framework Al on the structure of the active iron sites in Fe/ZSM-35

The influence of extra-framework Al via AlCl3 deposition on the structure of the active Fe sites in Fe/ZSM-35 was investigated by 29Si MAS NMR, UV–visible diffuse reflectance spectroscopy, infrared spectroscopy, UV Raman spectroscopy, and 57Fe Mössbauer spectroscopy combined with catalytic decomposition of N2O. It is found that high-temperature treatment considerably modifies the iron speciation. UV–visible diffuse reflectance spectra and in situ infrared spectra of NO adsorption show that a significant amount of clustered and cationic Fe species is transformed into extra-framework Fe–O–Al mixed oxide species by high-temperature treatment. UV Raman spectra and 57Fe Mössbauer spectra suggest the generation of a binuclear Fe site stabilized by extra-framework Al species with a feature Raman band at 875cm−1, which is associated with the high activity of N2O decomposition. A possible explanation is that the addition of extra-framework Al species is beneficial for the formation of binuclear active Fe sites bound to extra-framework Al.

Catalytic performance of sheet-like Fe/ZSM-5 zeolites for the selective oxidation of benzene with nitrous oxide

Hierarchical Fe/ZSM-5 zeolites were synthesized with a diquaternary ammonium surfactant containing a hydrophobic tail and extensively characterized by XRD, Ar porosimetry, TEM, DRUV–Vis, and UV-Raman spectroscopy. Their catalytic activities in catalytic decomposition of N2O and the oxidation of benzene to phenol with N2O as the oxidant were also determined. The hierarchical zeolites consist of thin sheets limited in growth in the b-direction (along the straight channels of the MFI network) and exhibit similar high hydrothermal stability as a reference Fe/ZSM-5 zeolite. Spectroscopic and catalytic investigations point to subtle differences in the extent of Fe agglomeration with the sheet-like zeolites having a higher proportion of isolated Fe centers than the reference zeolite. As a consequence, these zeolites have a somewhat lower activity in catalytic N2O decomposition (catalyzed by oligomeric Fe), but display higher activity in benzene oxidation (catalyzed by monomeric Fe). The sheet-like zeolites deactivate much slower than bulk Fe/ZSM-5, which is attributed to the much lower probability of secondary reactions of phenol in the short straight channels of the sheets. The deactivation rate decreases with decreasing Fe content of the Fe/ZSM-5 nanosheets. It is found that carbonaceous materials are mainly deposited in the mesopores between the nanosheets and much less so in the micropores. This contrasts the strong decrease in the micropore volume of bulk Fe/ZSM-5 due to rapid clogging of the continuous micropore network. The formation of coke deposits is limited in the nanosheet zeolites because of the short molecular trafficking distances. It is argued that at high Si/Fe content, coke deposits mainly form on the external surface of the nanosheets.

Catalytic decomposition of N2O over Ni and Mg-magnetite catalysts

The total decomposition of N2O was performed on the partially nanocrystalline substituted MxFe3−xO4 magnetite (M2+ = Ni2+ and Mg2+ with x = 0–1). The given results showed that the partial incorporation of Fe2+ by Ni2+ and Mg2+ into Fe3O4 spinel frameworks led to a significant amelioration in the catalytic activity for the N2O catalytic reaction. Furthermore, the catalytic activity of synthesized substrates depended on the Fe2+ substitution amount by Ni2+ and Mg2+ cations. The N2O conversion reached 20% (chemical regime) over the Ni0.75Fe2.25O4 and Mg0.58Fe2.42O4 catalysts at 395 and 404 K for N2O (5000 ppm), respectively. A relative increase of decomposition temperatures was observed after O2 addition. Moreover, other results show that the N2O conversion shifted to higher temperatures at high space velocities.

N2O catalytic decomposition over nano-sized particles of Co-substituted Fe3O4 substrates

A novel total decomposition of N2O was performed on the nano-sized particles of substituted CoxFe3−xO4 magnetite (with x=0–1). The given results showed that the partial incorporation of Fe2+ by Co2+ into Fe3O4 spinel substrate led to a significant amelioration in the catalytic activity for the N2O catalytic reaction. Furthermore, the catalytic activity of prepared substances depended on the Fe2+ substitution amount by Co2+ cation. The N2O conversion achieved 100% over the nano-sized Co0.6Fe2.4O4 catalyst at 255, 285 and 291°C for pure N2O, N2O with the presence of oxygen and N2O in the presence of water steam, respectively. A relative increasing of decomposition temperatures was observed after O2 addition. Moreover, the characterization of all samples showed that the catalyst surfaces contain nano-size particles accompanied by well distribution.

Preparation and characterisation of γ-Al2O3 particles-supported Rh/Ce0.9Pr0.1O2 catalyst for N2O decomposition in the presence of O2, H2O and NOx

A supported catalyst composed by the active phase Rh/Ce0.9Pr0.1O2 loaded on γ-Al2O3 particles was prepared and characterised by SEM, TEM, XRD, Raman spectroscopy, N2 adsorption at −196°C, H2-TPR and XPS. The catalytic decomposition of N2O was studied in simulated nitric acid plant streams (in the presence of O2, H2O and/or NOx) both in a fix-bed reactor and by in situ DRIFTS-MS experiments. The supported catalyst is able to decompose N2O from around 350–400°C in the presence of O2, H2O and/or NOx, and this temperature would be enough to decompose N2O in a nitric acid production plant after the expansion turbine, avoiding the use of an additional energy input. Among O2, H2O and NOx, NOx is the strongest inhibitor and O2 the weakest. The inhibiting effect of O2 is attributed to its reversible chemisorption on catalyst active sites, while the effect of H2O and NOx is mainly related with their irreversible chemisorption. The inhibition of H2O is not as high as that of NOx because the product of H2O chemisorption (Ce–OH surface groups) is suitable for N2O chemisorption and decomposition, while the surface nitrogen species created upon NOx chemisorption are not.

External Electric Field Catalyzed N2O Decomposition on Mn-Embedded Graphene

Adsorption ability and reaction rate are two essential parameters that define the efficiency of a catalyst. Herein, we study the effects of the external electric field F on the catalytic decomposition of N2O on a Mn-embedded graphene system (Mn/graphene) based on density functional theory calculations. Our study demonstrates that Mn/graphene has a better adsorption ability than the corresponding typical catalysts, such as platinum group metals, while the appropriate positive F can make the N2O decomposition spontaneously occur via a two-step mechanism of N2O → N2 + O and N2O + O → N2 + O2. In addition, F simultaneously facilitates O2 desorption and regeneration of the Mn/graphene system, completing the whole catalytic cycle. The high synergetic catalytic effect may be attributed to that F induces an enhancement of the charge transfer between N2O and Mn/graphene. Thus, the Mn/graphene system together with the synergy of F is a good candidate for N2O adsorptive decomposition.

Catalytic N2O decomposition on Pr0.8Ba0.2MnO3 type perovskite catalyst for industrial emission control

Ba substituted PrMnO3 type perovskite catalysts (Pr1−xBaxMnO3 with x=0.1–0.4) have been studied for N2O decomposition reaction. These catalysts were prepared by a combination of co-precipitation and impregnation methods. They are characterized in detail by means of XRD, BET-SA, SEM, EDX, O2-TPD, H2-TPR and XPS analysis. The catalytic activity of Ba substituted PrMnO3 catalyst was observed to be relatively better than the bare catalyst, thereby showing the promotional effect of barium, and Pr0.8Ba0.2MnO3 with 20mol% substitution was found to be the optimized composition. The Pr0.8Ba0.2MnO3 catalyst composition was also prepared in supported form using ceramic honeycomb by following in situ co-precipitation method and tested for N2O decomposition reaction under simulated feed conditions. Supported catalyst shows 92% conversion of N2O at 550°C with a maximum of 0.0984mmol of N2O decomposed per gram of the catalyst, per unit time in the presence of NO and O2, which was higher than that obtained for unsupported catalyst. O2-TPD studies inferred that Ba incorporation results in increase of Mn4+/Mn3+ ratio of PrMnO3 catalyst, thereby confirming the substitution of Ba in perovskite structure. TPR studies also provided the clear evidence to this effect. This improved redox property of Ba substituted perovskite catalyst was correlated to its enhanced catalytic activity for N2O decomposition.

Co3O4-KIT-6 composite catalysts: synthesis, characterization, and application in catalytic decomposition of N2O

Two sets of Co3O4-KIT-6 composite catalysts were prepared. To prepare the first set of catalysts, mesoporous silica (KIT-6) samples with different pore sizes were obtained by changing the hydrothermal temperature during synthesis, and the same amount of Co3O4 (10 %) was loaded by impregnation. In the second set, KIT-6 prepared by hydrothermal synthesis at 100 °C was used to load different amounts of Co3O4 (up to 50 %). These materials were characterized by low-angle and wide-angle X-ray diffraction, transmission electron microscopy (TEM), and N2 adsorption–desorption. The TEM results showed that Co3O4 species do not disperse on the inner pores of KIT-6 homogeneously, nor do they form separate Co3O4 particles detached from KIT-6. Rather, Co3O4 crystals grow into the KIT-6 matrix, forming Co3O4-KIT-6 composite grains in some parts of the KIT-6 matrix, whereas there are empty mesoporous silica channels in other parts. The influences of textural properties of KIT-6 support and the loading of Co3O4 on the catalytic activity in N2O decomposition were studied. It was found that the textural properties (e.g., pore size, surface area) of KIT-6 have little effect on the catalytic activity, whereas the amount of Co3O4 directly correlates with the catalytic activity.

Study on Catalytic Decomposition of N<sub>2</sub>O over Modified Zeolites

A series of Beta, ZSM-5 and MCM-22 zeolites modified with metal ions (such as Fe 3+ , Co 2+ , Ce 3+ , Ni 2+ and Cu 2+ ) for catalytic decomposition of N2O were prepared by using wet ion exchange method. The effects of different metal ions, the contents of metal ions and silicon aluminum ratio on catalytic decomposition activities of N2O were investigated, respectively. The results indicated that Beta with a SiO2/Al2O3=30 and 1% Fe 3+ have better catalytic decomposition activities to N2O, the completed catalytic decomposition temperature to 35% N2O in the condition of 4000 h-1 GVSH is 350 0 C.

Catalytic decomposition of N2O over CuxCe1−xOy mixed oxides

The catalytic N2O decomposition was investigated over a series of CuxCe1−xOy mixed oxides with different Cu/Ce molar ratios. Effects of synergy over mixed oxides of CeO2 and CuO were observed significantly, the catalyst of Cu0.67Ce0.33Oy exhibited the high activity among the Cu–Ce–O mixed oxides for N2O decomposition. Characterizations of XRD, N2-adsorption, XPS, and H2-TPR were applied to correlate their properties with the corresponding catalytic performance, and reveal the synergetic effect between CuO and CeO2 for N2O decomposition. In situ DRIFTS investigation confirmed the presence of CuI species that was closely related with the activity of CuxCe1−xOy catalyst. The synergy of CuxCe1−xOy promoted the stability and the ability to regenerate the active CuI site.

Substituted ferrite M Fe1−Fe2O4 (M = Mn, Zn) catalysts for N2O catalytic decomposition processes

The N2O catalytic decomposition to N2 and O2 as gas products was carried out on the substituted ferrite MxFe1 − xFe2O4 (M = Mn and Zn with x = 0 − 0.8) catalysts. The obtained results showed that the partial substitution of Fe by Mn and Zn metal transitions in Fe3O4 spinel oxide led to a significant improvement in the catalytic activity for the N2O decomposition. Moreover, the catalytic activity depended on the degree of Fe replacement by Mn or Zn. The N2O conversion reached 100% over the Mn0.8Fe0.2Fe2O4 and Zn0.6Fe0.4Fe2O4 catalysts at 250 and 280 °C for pure N2O, respectively. The decomposition temperatures were relatively increased after O2 addition.

A comparative study of TiO2-supported and bulk Co–Mn–Al catalysts for N2O decomposition

A series of Co–Mn–Al/TiO2 catalysts with different Co+Mn loading (5–24wt.%) was prepared by impregnation of TiO2 support. Bulk Co–Mn–Al mixed oxides were prepared by different methods. The prepared catalysts were characterized by chemical analysis, surface area measurement, temperature programmed techniques (TPR, TPD) and tested for N2O catalytic decomposition. TiO2 acted only as a catalytic support and did not contribute to the catalytic activity. The N2O conversion over TiO2-supported Co–Mn–Al catalysts was increasing with Co+Mn loading, and was proportional to the amount of easily reducible components. Comparing the catalysts with identical amount of active components, the highest catalytic activity was achieved on the calcined precursors having carbonates in their molecules (layered double hydroxides Co–Mn–Al-HT-ex and Co–Mn–Al-carb), the lowest one on the calcined Co–Mn–Al nitrates due to the lower surface area, less advantageous porous structure and worse reducibility.

N2O catalytic decomposition – From laboratory experiment to industry reactor

Paper deals with design of pilot reactor for low temperature N2O decomposition in off-gases from HNO3 production. Pseudo-homogeneous one-dimensional model of an ideal plug flow reactor was used for modeling of N2O decomposition in a laboratory fixed bed reactor filled with grains or pellets of a Co–Mn–Al mixed oxide catalyst. Increase in inlet pressure up to 0.6MPa did not influence the effective diffusion coefficient, but improved the achieved N2O conversion. Based on the laboratory data of N2O decomposition over Co–Mn–Al mixed oxide pellets, catalyst bed of 3400kg was estimated for target 90% N2O conversion (30000m3h−1 of exhaust gases from HNO3 plant containing 0.1molar% N2O, 0.01molar% NO, 0.01molar% NO2, 3molar% H2O, 5molar% O2) at 420°C and 600kPa inlet pressure.

Nanostructured Co–Ce-O systems for catalytic decomposition of N2O

Two series of nanostructured materials were obtained by the reverse microemulsion method. It was confirmed obtaining of the nanometric crystallites of Co-substituted ceria solid solutions up to 15mol% of Co, while the reverse oxide system was biphase, even at so low content of CeO2 as 1mol%. The differences in pores structure of the both series were observed as well as the size of crystallites, however limited within nanometric range. The biphase materials showed higher catalytic activity than the solid solutions of Co in ceria phase, though this activity increased with Co content in CeO2 phase.

Copper ionic pairs as possible active sites in N2O decomposition on CuOx/CeO2 catalysts

Synthesized by impregnation and coprecipitation methods, ceria-supported copper samples were tested in catalytic decomposition of N2O (deN2O) under dry and wet conditions. Basing on the structural (XRD, SEM), spectroscopic (EPR, RS) and catalytic characterization, supported by DFT calculations, the role of mono- and dimeric copper as active centers in the deN2O reaction was evaluated. Particular attention was paid to elucidation of the structure and localization of the Cu2+Cu2+ pairs within the CeO2 matrix, their stability and chemical conditions of their formation.

Ordered mesoporous NiCoMnO4: synthesis and application in energy storage and catalytic decomposition of N2O

Ordered nanocrystalline mesoporous NiCoMnO4 samples were prepared using mesoporous silica (KIT-6) as a hard template, and characterized by Powder X-Ray Diffraction (PXRD), Transmission Electron Microscopy (TEM), Energy Dispersive X-ray Spectroscopy (EDX), and N2 adsorption–desorption. The average crystal sizes and textural properties of mesoporous NiCoMnO4 could be tuned by varying the annealing temperature (200–800 °C) during the synthesis. The applications as an electrochemical capacitor and in catalytic decomposition of N2O were demonstrated. Mesoporous LiNi1/3Co1/3Mn1/3O2 was further prepared by reacting mesoporous NiCoMnO4 with LiOH at 400 °C, and its application as a cathode material for Li-ion batteries was demonstrated.

Improved structural and catalytic attributes of Ba2Co2Fe12−2x(Zr,Ni)xO22 materials synthesized by sol–gel and microwave heating methods

Nominal composition of Zr–Ni co-doped Ba2Co2Fe12−2x(Zr,Ni)xO22 (x = 0.2–1.0) Y-type hexaferrites were synthesized by conventional sol–gel and microwave heating methods. Structural analysis was carried out by TGA, SEM, XRD, O2-TPD and BET surface area. Microwave synthesized samples revealed good morphological properties with high surface area and high porosity compared to that obtained by the sol–gel method. Catalytic decomposition of N2O was achieved at low temperatures of 600 °C and 700 °C for microwave and sol–gel prepared samples, respectively. The catalysts are found workable and stable even at 1146 °C with very good N2O decomposition efficiency. Substituting iron with Zr–Ni further enhanced the catalytic activity in both the cases.

Decomposition of nitrous oxide over Co-zeolite catalysts: role of zeolite structure and active site

A series of Co exchanged zeolites with ZSM-5, BEA, MOR and USY structures were prepared and investigated for N2O catalytic decomposition under identical reaction conditions. It is found that Co-zeolites with different structures show dramatically different catalytic activities, which could be attributed to various Co species formed in them. Co-ZSM-5, Co-BEA and Co-MOR exhibit much higher activities than Co-USY catalysts, which is attributed to the predominant formation of active isolated Co2+ ions in the ion exchange positions; while in Co-USY Co mainly exists as less active Co oxides. Moreover, it is observed that the activities of Co2+ ions in ZSM-5, BEA and MOR zeolites are quite different and are related to the specific Co ion sites presented in each zeolite structure. In Co-ZSM-5, the most active sites are the α-type Co ions, which are weakly coordinated to framework oxygens in the straight channel. On the other hand, in Co-BEA and Co-MOR, the most active sites are β-type Co ions, which are coordinated to the framework oxygens of the elongated six-membered ring of BEA and the interconnected small channel of MOR, respectively. The main factors affecting the activities of these individual Co ions are indicated to be their location in the zeolite structure, their chemical coordination and the distances between the Co ions. The highest activity of the α-type Co ions in ZSM-5 could be attributed to their favorite location in the zeolite and weak coordination to framework oxygens, which make them easily accessible and coordinated to reactants. The large number of β-sites and their structural arrangement in MOR allow the formation of two unique adjacent β-Co ions in Co–Co pairs, which cooperate in N2O splitting, consequently yielding the high activity of β-Co ions in MOR.

Computational and Experimental Investigations into N2O Decomposition over MgO Nanocrystals from Thorough Molecular Mechanism to ab initio Microkinetics

In this article a comprehensive molecular modeling of the reaction mechanism complemented by ab initio microkinetic modeling of the catalytic decomposition of N2O on MgO nanocrystals is discussed. The density functional level of theory was used to study the molecular mechanism of conceivable elementary steps of the deN2O reaction over the most stable (100) surface, including the effect of surface morphology. It is shown that terrace sites are responsible for steady state reactivity, whereas the more basic and reactive sites located on edges and corners are involved only in the initial stages of the reaction because of poisoning. Detailed analysis of the reaction progress in terms of the energy profiles and the evolution of partial charges and bond orders for each step allowed for an in-depth insight at the atomic scale into the nature of the catalytic N2O decomposition over anionic redox active sites constituted by surface O2– ions. The harmonic transition state theory along with the calculated free enthalpies of activation were used to model the reaction progress in pulse (transient) and steady state regimes as well as to predict the kinetic isotopic effects (KIE) for 15N and 18O labeled reactants. The proposed kinetic scheme was able to reproduce the results of temperature-programmed surface reaction and KIE experiments with high accuracy without fitting of any parameters.

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.