Catalytic Decomposition Of N2O Research Articles

Iron-exchanged FAU zeolites: Preparation, characterization and catalytic properties for N2O decomposition

New Fe-FAU zeolitic catalysts made from large channel zeolite matrix FAU by a simple wet ion exchange method show an excellent performance in N2O catalytic decomposition. The ion exchange process was discussed in detail and the optimal conditions for wet ion exchange were proposed. The formation of various iron sites in Fe-FAU samples (isolated Fe ions, oligonuclear clusters and Fe2O3 nanoparticles) during preparation process was extensively investigated by means of UV–vis spectra, FTIR spectra of NO adsorption, TEM images, H2-TPR and 27Al MAS-NMR spectra. We have found that Fe(III)-FAU catalysts more effectively decompose N2O with/out NO-assistance than other Fe-zeolite (such as Fe-MFI) catalysts prepared in the same way. Comprehensive understanding of the structure properties and the catalytic performance suggests that different iron sites in Fe-FAU make different contributions to N2O thermal decomposition and that isolated/oligonuclear iron species contribute more due to their high accessibility towards N2O. In addition, the high durability of Fe-FAU catalysts is proposed to account for the particular interactions between iron species and zeolite framework.

Direct NO decomposition over La2−xBaxNiO4 catalysts containing BaCO3 phase

La2−xBaxNiO4 (x≤1.2) catalysts have been prepared by citrate method. XRD patterns and IR spectra indicate that with the doping of Ba, more BaCO3 appears and perovskite-like structure is seriously distorted. In directly decomposing 4% NO, the highest N2 yield is achieved with La1.2Ba0.8NiO4 composed of perovskite-like structure phase and BaCO3 in the absence/presence of oxygen. The results of iodometry and H2-TPR reveal that the increase in Ba causes the increase in Ni3+ content. O2-TPD and NO adsorption tests confirm that Ba doping resulted in the increase in oxygen vacancy (Vo). Thus, the redox capability and the amount of Vo are enhanced. It is suggested that the BaCO3 phase, NOx storage component, contributes to the increase in activity by NO-TPD, NO2-TPD and in situ DRIFT. Thus, BaCO3 plays an important role in quickening up the run of catalytic NO decomposition recycle.

Application of Calcined Layered Double Hydroxides as Catalysts for Abatement of N2O Emissions

The results of catalytic decomposition of N2O over mixed oxide catalysts obtained by calcination of layered double hydroxides (LDHs) are summarized. Mixed oxides were prepared by thermal treatment (500 °C) of coprecipitated LDH precursors with general chemical composition of MII1-xMIIIx(OH)2(CO3)x/2·yH2O, where MII was Ni, Co, Cu and/or Mg, MIII was Mn, Fe and/or Al, and the MII/MIII molar ratio was adjusted to 2. The influence of chemical composition of the MII-MIII mixed oxide catalysts on their activity and stability in N2O decomposition was examined. The highest N2O conversion was reached over Ni-Al (4:2) and Co-Mn-Al (4:1:1) catalysts. Their suitability for practical application was proved in simulated process stream in the presence of O2, NO, NO2 and H2O. It was found that N2O conversion decreased with increasing amount of oxygen in the feed. The presence of NO in the feed caused a slight decrease in N2O conversion. A strong decrease in the reaction rate was observed over the Ni-Al catalyst in the presence of NO2 while no N2O conversion decrease was observed over the Co-Mn-Al catalyst. Water vapor inhibited the N2O decomposition over all tested catalysts. The obtained kinetic data for N2O decomposition in a simulated process stream over the Co-Mn-Al catalyst were used for a preliminary reactor design. The packed bed volume necessary for N2O emission abatement in a HNO3 production plant was calculated as 35 m3 for waste gas flow rate of 30 000 m3 h-1.

N2O decomposition over the circulating ashes from coal-fired CFB boilers

The catalytic decomposition of N2O over the circulating ashes from coal-fired circulating fluidized bed (CFB) boilers was investigated with a fixed bed reactor. The associated kinetics was mimicked by four surrogate metal oxides of SiO2, Al2O3, CaO and Fe3O4, which were found as the main components of the circulating ashes. The activation energies and collision coefficients for N2O thermal decomposition over the circulating ashes and surrogates were individually measured. Experimental results showed that different metal oxides play different roles in the catalytic decomposition of N2O. Among the components, CaO and Fe3O4 are very active, while Al2O3 and SiO2 contribute much less to N2O destruction. A model based on the specific surface-area-weighted kinetic data of individual surrogates was developed to predict the catalytic decomposition of N2O over circulating ashes. The predictions agreed with the experimental data with a minor discrepancy acceptable in an engineering view. Some discussions on the discrepancy were given. The O2 effect on the N2O decomposition over the circulating ashes was experimentally assessed. It was found that the presence of O2, even with a small amount, would deteriorate the catalytic decomposition of N2O.

Trends in catalytic NO decomposition over transition metal surfaces

The formation of NOx from combustion of fossil and renewable fuels continues to be a dominant environmental issue. We take one step towards rationalizing trends in catalytic activity of transition metal catalysts for NO decomposition by combining microkinetic modelling with density functional theory calculations. We show specifically why the key problem in using transition metal surfaces to catalyze direct NO decomposition is their significant relative overbinding of atomic oxygen compared to atomic nitrogen.

Validation of the catalytic properties of Cu-Os/13X using single fixed bed reactor in selective catalytic reduction of NO

Catalytic decomposition of NO over Cu-Os/13X has been carried out in a tubular fixed bed reactor at atmospheric pressure and the results were compared with literature data performed by high-throughput screening (HTS). The activity and durability of Cu-Os/13X prepared by conventional ion-exchange method have been investigated in the presence of H 2O and SO 2. It was found that Cu-Os/13X prepared by ion-exchange shows a high activity in a wide temperature range in selective catalytic reduction (SCR) of NO with C 3H 6 compared to Cu/13X, proving the existence of more NO adsorption site on Cu-Os/13X. However, Cu-Os/13X exhibited low activity in the presence of water, and was quite different from the result reported in literature. SO 2 resistance is also low and does not recover its original activity when the SO 2 was blocked in the feed gas stream. This result suggested that catalytic activity between combinatorial screening and conventional testing should be compared to confirm the validity of high-throughput screening.

Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst

A series of CeO2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N2O). Addition of CeO2 to Co3O4 led to an improvement in the catalytic activity for N2O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N2O conversion could be attained over the CoCe0.05 catalyst below 400°C even in the presence of O2, H2O or NO. Methods of XRD, FE-SEM, BET, XPS, H2-TPR and O2-TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO2 could increase the surface area of Co3O4, and then improve the reduction of Co3+ to Co2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N2O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO2, are responsible for the enhancement of catalytic activity of Co3O4.

팩 베드 형상을 가지는 N2O 촉매 점화기의 열적현상

In this paper, thermal characteristics of a nitrous oxide (N₂O) catalytic reactor with packed-bed geometry are theoretically and numerically investigated. Several researchers experimentally presented that catalytic decomposition of N₂O in a packed bed generates about 82kJ/㏖e in the exothermic reaction. Based on the results they have studied the catalytic decomposition of N₂O in a packed bed to use it not only as a monopropellant thrust for small satellites but also as an igniter system for hybrid rockets. So we aim to identify important parameters existing in an N₂O packed-bed geometry, and to clarify its critical effect on thermal characteristics of the catalytic igniter using a porous medium approach.

Decomposition of N2O over Hexaaluminate Catalysts

Catalytic N2O decomposition has been studied over metal-substituted hexaaluminates with the general formula ABAl11O19, where A = La, Ba, and B = Mn, Fe, Ni. The materials were prepared by coprecipitation via the carbonate route followed by calcination at 1473 K for 10 h. Inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), transmission electron microscopy (TEM), and N2 adsorption techniques were used to characterize the catalysts. The activity in direct N20 decomposition was evaluated by means of temperature-programmed reaction and steady-state experiments. Fe- and Mn-containing hexaaluminates present the highest activities. The Ni-containing catalysts are significantly less active, comparable to the hexaaluminates without metal substitution. The catalytic activity was practically not influenced by the A cation (La or Ba) in the structure. The Fe- and Mn-substituted hexaaluminates exhibit high activity and stability for N2O decomposition in mixtures simulating the outlet of the Pt-Rh gauzes in ammonia oxidation reactors, containing N2O, NO, O2, and H2O. These materials are promising for high-temperature abatement of this powerful greenhouse gas in the chemical industry, particularly in nitric acid and caprolactam production.

Catalytic Decomposition of N<SUB>2</SUB>O over Co-M(M=La, Ce, Fe, Mn, Cu, Cr) Composite Oxide Catalysts

A series of Co-M (M=La, Ce, Fe, Mn, Cu, Cr) composite oxide catalysts were prepared by co-precipitation method and tested in catalytic decomposition of N2O. The results showed that Co-Ce composite oxide with Ce/Co molar ratio of 0.05 (CoCe0.05 catalyst) performed best in the N2O decomposition reaction. The presence of NO and O-2 in the feed affected the decomposition rate of N2O over CoCe0.05 by adsorption of nitrate or nitrite species on the active site. The XRD, BET, O-2-TPD, and H-2-TPR methods were used to characterize the Co-M mixed catalysts. The analysis results showed that the redox ability of the active site (Co2+) was very important for the decomposition of N2O over these catalysts. The surface decomposition of N2O was accompanied by the oxidation of Co2+ to Co3+, and the desorption of surface oxygen was accompanied by the reduction of Co3+ to Co2+. The addition of other transition metal oxides except CeO2 lowered the redox ability of Co3+/Co2+, and thus lowered the catalytic activities for the decomposition of N2O. In addition, the rate-determining step of the catalytic N2O decomposition was also influenced by the addition of various metal oxides.

Comparison of the activity of Ru and Pt catalysts for the oxidation of carbon by NO2

The role of two catalysts Pt/Al2O3 and Ru/NaY on the oxidation of carbon by NO2 was investigated in the temperature range 300–400°C. In the case of Pt/Al2O3 no significant catalytic effect on the carbon oxidation rate is observed although decomposition of NO2 takes place on the noble metal and leads to the formation of NO. This result suggests that the amount of the oxygen atoms transferred from the metallic surface sites to the carbon surface to form C(O) complex is negligible. In contrast, in presence of Ru/NaY the oxidation rate of carbon by NO2 is markedly increased. Hence, a significant part of the formed O through catalytic decomposition of NO2 on Ru surface sites is transferred to the carbon surface leading to a larger amount of C(O) complexes on the carbon surface. Thus, the ruthenium surface is a generator of active oxygen species that are spilled over on the carbon surface at 350°C.

Direct NO and N 2O decomposition and NO-assisted N 2O decomposition over Cu-zeolites: Elucidating the influence of the Cu [sbnd]Cu distance on oxygen migration

Several zeolites of varying topology and with different Cu/Al ratios were investigated in the catalytic decomposition of NO, N 2O and the NO-assisted N 2O decomposition. The highest activity in the direct NO and N 2O decomposition was found for bis( μ-oxo)dicopper cores in Cu-ZSM-5 followed by the EPR silent Cu in MOR, FER and BEA, while almost no activity was observed over the isolated, EPR detectable Cu sites. This sequence of decreasing activity follows the increasing average distance between Cu sites. An average volume of 35 Å 3 per Cu atom (average Cu Cu distance 4.1 Å) appears to be a threshold value separating high and low activity. The high activity for catalysts with small Cu Cu distances is explained by facile oxygen migration over the Cu sites, enabling recombination into gaseous O 2. When the distance between the Cu centers is increased, oxygen migration is hampered. Adding NO results in the scavenging of the deposited O atoms, thereby transporting them into the gas phase. Hence an alternative oxygen migration pathway is created that has the greatest impact on activity of the isolated EPR-detectable Cu sites and a negative effect on the bis( μ-oxo)dicopper cores in Cu-ZSM-5.

Iron ions in ZSM-5 zeolite: Fe3+ in framework, Fe2+ in extra-framework positions in catalytic N2O decomposition

Fe-ZSM-5 samples containing a combination of 57Fe3+ in framework (FW) and regular iron in extra-framework (EFW) sites were prepared by introducing 57Fe in hydrothermal synthesis, then exchanging Fe2+ of natural isotope composition into the lattice. The stability for one part of Fe2+ and Fe2+ ↔ Fe3+ reversibility for the other part in catalytic decomposition of N2O is demonstrated by in situ Mossbaer measurements. Formation of dinuclear FeFW–O–FeEFW pairs is not prevailing.

Thermodynamic features of the Cu-ZSM-5 catalyzed NO decomposition reaction

Over a Cu-ZSM-5 catalyst with a quantified amount of the active Cu2+-dimers (Cu2+-O2--Cu2+), the kinetics of the catalytic NO decomposition to N2 and O2 was derived on the basis of the proposed reaction mechanism, and such thermodynamic data as adsorption enthalpies of NO and O2 onto the Cu ion dimer sites were evaluated. It was revealed that the enthalpy of the adsorption of NO (δH=-34.1 kcal/mol) onto a reduced Cu+-dimer, as the initiating step of NO decomposition catalysis, was higher than that (δH=-27.8 kcal/mol) onto an oxidized Cu2+-dimer, or that (δH=-27.4 kcal/mol) of the dissociative adsorption of O2 onto the two reduced Cu+-dimers in neighbor. The strong inhibition effect of gas phase oxygen on the kinetic rate of NO decomposition at 400–600 ‡C could be explained by the thermodynamic predominance of the oxidized Cu2+-dimers against the active reduced Cu+-dimers on the catalyst even at high temperature and under the low partial pressure of oxygen. It was also found that the maximum catalytic activity at temperatures around 500 ‡C, which was commonly observed in the Cu-ZSM-5 catalyzed NO decomposition reaction, was attributed to the relatively large enthalpy of NO adsorption onto the reduced Cu+-dimers as compared to that of the reaction activation energy (=19.5 kcal/mol), resulting in less favored NO adsorption at the higher temperatures than 500 ‡C.

NO decomposition over a Pd/MgO catalyst prepared from [Pd(acac)2

A Pd/MgO catalyst was prepared by adsorption of palladium bis-acetylacetonate [Pd(acac)2] onto highly dehydroxylated MgO from toluene solution and subsequent reduction in flowing H2 at 300°C. The resultant catalyst was characterized by Pd K-edge X-ray absorption fine structure (XAFS) spectroscopy, temperature-programmed desorption (TPD), and Fourier transform infrared (FTIR) spectroscopy of adsorbed NO. The adsorbed [Pd(acac)2] species decomposes on heating in H2 to form 20–25Å supported Pd particles; however, organic residues from the acetylacetonate ligands remain on the catalyst surface. The FTIR spectrum of NO adsorbed on the reduced Pd/MgO catalyst at 25°C contains one principal band at 1722cm−1 due to atop Pd nitrosyl species. In situ XAFS of the Pd/MgO catalyst indicates that neither Pd oxidation nor particle sintering occurs during heating in flowing 1% NO/He to 300°C. NO decomposition over the Pd/MgO catalyst was investigated using temperature-programmed reaction spectroscopy (TPRS) and steady-state activity measurements. During the initial TPRS cycle in flowing 1% NO/He, nearly complete NO consumption occurs at ∼270°C due to oxidation of organic residues. O2 evolution commences at approximately 350°C, and steady-state catalytic decomposition of NO to N2 and O2 occurs at 600°C. Transient NO consumption during rapid cooling in 1% NO/He (after steady-state catalysis) is attributed to NOx adsorption on the Pd/MgO catalyst.

Catalytic Decomposition of N2O over the Bed Material from Circulating Fluidized-Bed (CFB) Boilers Burning Biomass Fuels and Wastes

In this paper, the catalytic decomposition of N2O was studied over the bed materials sampled from the bottom bed of two industrial circulating fluidized-bed (CFB) boilers (a 12 MWth boiler and a 550 MWth boiler) burning biomass fuels and wastes, either alone or as a mixture. The catalytic activity of the bed materials were compared by measuring the conversion of N2O in a laboratory fixed-bed reactor in the temperature range of 600−910 °C. The composition and morphology of the bed material were characterized using X-ray fluorescence and scanning electron microscopy coupled with energy-dispersive X-ray analysis. The activity of bed material was observed to be affected by the sample heterogeneity and tendency to deactivate when exposed to fluidized-bed temperatures. The activity of the bed materials was also influenced by the type of fuel, for which the kinetic expressions are derived. For the bed-material samples from the 12 MWth CFB boiler, it was observed that the higher the amount of the catalytically active oxides (CaO + MgO + Fe2O3 + Al2O3), the higher the activity of the sample toward N2O decomposition. The elemental composition of the surface of the bed material particles changed according to the composition of the ash from the parent fuel. On the other hand, such correlations were not observed for the samples from the 550 MWth CFB boiler.

From first principles to catalytic performance: tracking molecular transformations

Ab initio methods can be used to elucidate the nature of active sites as well as the influence of the surrounding environment on catalytic kinetics. Theory can be coupled with atomic scale simulation in order to track the molecular transformations that occur over different surfaces and assess their catalytic activity and selectivity. Herein we describe the application of theory and simulation to two specific example systems, the catalytic decomposition of NO under lean conditions, and the electrocatalytic oxidation of methanol over Pt. The results for NO decomposition under lean conditions show how density functional theory calculations and kinetic Monte Carlo simulation can used to begin to tailor the metals that are used, the alloy composition, and the specific atomic arrangements at the surface in order to optimize catalytic performance. Alloying Pt with nearly 50% Au leads to turnover rates that are nearly four times larger than Pt surface alone. The specific arrangement of Pt and Au create special Pt “+-site” ensembles that reduce surface poisoning by oxygen. In the second example, we describe the elementary pathways for methanol decomposition to CO in both the vapor as well as the liquid phase. The presence of solution significantly alters the overall reaction energies by stabilizing charged complexes that form. The presence of solution drives the heterolytic activation of C–H and O–H bonds over Pt rather than the homolytic activation thus leading to the generation of protons in the aqueous media. In addition, an external potential can be applied in order to model electrochemical systems. These effects are found to be quite important in the electrochemical phase behavior of water over Pt.

Characterization of Cuprous Ion in High Silica Zeolites and Reaction Mechanisms of Catalytic NO Decomposition and Specific N2 Adsorption

AbstractFor Abstract see ChemInform Abstract in Full Text.

On the Role of Different Adsorption and Reaction Sites on Supported Nanoparticles during a Catalytic Reaction: NO Decomposition on a Pd/Alumina Model Catalyst

We have studied the catalytic decomposition of NO on a structurally well-defined Pd model catalyst, employing a combination of molecular beam techniques and time-resolved IR reflection absorption spectroscopy (TR-IRAS). In a first step, different active sites such as facets and edges/defects on the catalyst nanoparticles are identified spectroscopically. Subsequently, these spectroscopic signatures are utilized to monitor the site occupation by reactant species (NO) and products (atomic oxygen and nitrogen) under reaction conditions. Simultaneously, the kinetics of NO dissociation is investigated. It is found that atomic nitrogen and oxygen species are initially formed in the vicinity of edge or defect sites. At temperatures up to 300 K, the mobility of these atomic species is suppressed, whereas at higher temperature, diffusion onto the (111) facets of the particles can occur. It is shown both by IR spectroscopy of adsorbed NO under reaction conditions and by control experiments using CO as a probe molecule that nitrogen and oxygen species preferentially occupy particle edge and defect sites. By means of molecular beam CO titration experiments and TR-IRAS, it is demonstrated that the presence of these atomic species critically controls the NO dissociation activity. Specifically, the presence of strongly bound nitrogen in the vicinity of edge and defect sites gives rise to an enhanced dissociation probability under conditions of high adsorbate coverage.

Catalytic decomposition of N2O

Decomposition of N2O in the temperature range 200–500°C was studied on catalysts composed of rhodium supported on γ-Al2O3 doped with different amounts of Li, Na, K, Cs cations. It has been found that doping with alkali metals influences the dispersion of rhodium which is reflected in the changes of catalytic activity. Dependence of activity on dispersion is linear for potassium and cesium, whereas in the case of sodium a dramatic decrease of activity is observed when the concentration of sodium surpasses 0.07–0.08mol% due to the modification of the number or specific activity of active sites. The detrimental effect of sodium may be compensated by doping with potassium.