High Temperature N2O Decomposition Research Articles

High-temperature decomposition of N2O from the HNO3 production: Process feasibility using a structured catalyst

The high-temperature decomposition of N2O in a structured catalyst was studied using a full three-dimensional (3D) model in the temperature range 700–900 °C and high pressure (0.4–0.8 MPa), under realistic gas phase composition, i.e. with 1000 ppm of N2O, high concentrations of NO (9.5–10.5 mol%), O2 (4.5–5.0 mol%), and H2O (15.5–16.8 mol%). The kinetic data gathered from the previous study of the FeOx/Al2O3 catalyst displaying only medium activity were used as the input data. A single-channel 3D model without additional simplifications of fluid flow patterns and mass transfer in fluid and solid catalyst phases was employed to investigate the potential performance of a monolith reactor for N2O decomposition at high temperature regime. The model clearly predicted a relevant performance of the optimized honeycomb system based on such FeOx/Al2O3 catalyst.

Preparation of LaNiO3 perovskite by oxalate and carbonate precursor method for utilization as catalyst for high-temperature decomposition of N2O

The mixed oxide LaNiO3 with perovskite structure was prepared by two relatively new and unconventional methods including preparation and thermal decomposition of mixed metal oxalate or carbonate precursors. The intermediates were prepared by reaction in a highly concentrated suspension (paste). The thermal decomposition conditions of these intermediates were described, and the final calcination temperatures were determined, which were done using thermal analysis methods and X-ray diffraction. During the decomposition of mixed carbonates, one-phase LaNiO3 is produced directly, and in case of decomposition of oxalates, a mixture of LaNiO3 and La2O3 is produced due to the formation of La2O2CO3 during the heating. Catalytic decomposition of nitrous oxide at high temperature (650–930 °C) and high loading (GHSV = 350,000 h−1) has shown high LaNiO3 activity, even at lower temperatures. The results were compared with the same compound obtained by co-precipitation and by solid-state reaction. Methods of preparation based on decomposition of oxalate and carbonate intermediates lead to the preparation of materials with appropriate composition, morphology, specific surface and high catalytic activity.

Structural stability of metal containing ferrierite under the conditions of HT-N2O decomposition

Abstract Ferrierite based catalyst is expected to be used for high-temperature decomposition of N2O. The stability of the ferrierite structure and divalent cations in ferrierite in this process were analysed using XRD, SEM, FTIR, 27Al and 29 Si MAS NMR. This study provides detailed information regarding to Al removal from zeolite that is either involved in the Bronsted acid sites or formation of local cationic sites responsible for bonding divalent cations. The Al atoms, which stabilize divalent cations in cationic positions, have the potential to be resistant to prolonged exposure to the conditions of high-temperature decomposition of N2O. The presence of water led to the destruction of the iron active sites for N2O decomposition in iron ferrierite. Moreover, the negative role of residual sodium ions eventually remaining in the commercial ferrierite was proven to induce the irreversible collapse of the zeolite framework.

On the mechanism of high-temperature N2O decomposition over Fe-FER in the presence of NO

The role of NO in the N2O decomposition under conditions relevant to its formation by NH3 oxidation during nitric acid production over iron-containing ferrierite (Fe-FER) catalyst was investigated. In particular, the relative productions of O2 and NO2 during the high-temperature decomposition of N2O over Fe-FER as the result of the direct recombination of adsorbed atomic oxygen (Oat) and of NO oxidation steps, respectively, were evaluated. These results proved the enhanced role of the direct Oat recombination step at higher temperatures but surprisingly also indicated persistent and substantial elimination of N2O due to NO oxidation during the formation of NO2 at T ≥ 800 °C.

FeOx/Al2O3 catalysts for high-temperature decomposition of N2O under conditions of NH3 oxidation in nitric acid production

The δ and θ Al2O3 phases well stabilized Fe(iii) in Td or Oh coordination, which were identified as the active species in high temperature decomposition of N2O in a complex gas mixture produced by oxidation of ammonia.

Feasibility of application of iron zeolites for high-temperature decomposition of N2O under real conditions of the technology for nitric acid production

The long-term stabilities of a group of iron zeolites with MFI, *BEA, and FER structures and similar Fe/Al ratios were evaluated to assess their performance as catalysts for N2O decomposition. Conditions relevant for the application of the catalyst at the secondary level for N2O elimination, i.e., directly after the NH3 oxidation step of the process of nitric acid production, were investigated. These conditions included reaction temperatures of up to 900°C and the presence of high concentrations of water vapour, oxygen, and NO. The focus of the study was the comparison of the MFI and *BEA zeolites with the FER-based zeolite, a catalyst established as relatively stable under such conditions. The structural analysis of the individual zeolite frameworks and iron species involved a combination of several methods, and provided insight into the framework modification as well as identification and semiquantitative determination of the individual iron species. In the zeolite catalysts, these iron species were in the form of either isolated Fe(II) and Fe(III)-oxo ions, polynuclear Fe(III)-oxo complexes, or small Fe oxide particles. None of the zeolite structures displayed a high extent of structural collapse of the framework; thus, structural collapse does not explain the observed decrease in activity. An investigation of the kinetics of the N2O decomposition, both before and after ageing under relevant reaction conditions, proved the dominant role of isolated Fe(II) ions that were accessible to the reacting gas-phase molecules. The kinetic study also identified the differences in the ability of the three zeolites to stabilize the active sites in individual framework types during long-term exposure to challenging reaction conditions. It has been shown that, while the isolated Fe(II) ions were present in adequate concentration for N2O decomposition activity at the relevant temperature region in all three zeolite-based catalysts, the MFI and *BEA zeolites were not able to effectively stabilize the active iron structure during ageing for over 12days. In contrast, the FER framework survived a test for over 24days. The iron species formed in MFI and *BEA zeolites during ageing were mostly large FeOx species and displayed very low activity that approached the activity of FeOx clusters supported on SiO2.

Technical Engineering for Catalytic Reduction of Nitrous Oxide Emissions

AbstractProduction of nitric acid is the major emission source of the greenhouse gas nitrous oxide N2O. High temperature catalytic decomposition of N2O by installing a secondary catalyst has been applied at a nitric acid plant in Devnya, Bulgaria. A reconstruction of the ammonia burning reactors was done in august 2012 in order to increase the thickness of the secondary catalyst layer from 28 mm to 60 mm. Nitrous oxide concentration has been monitored for 5 year period – from 2010 to 2014. Monitoring results indicate that the effectiveness of N2O catalytic decomposition depends on the thickness of the secondary catalyst layer – increasing the layer thickness twice leads to over 60 % reduction of the maximum registered and annual average concentrations of N2O. Increasing the thickness of the secondary catalyst layer enhances the effectiveness of high temperature N2O decomposition, which is essential for the parties to the United Nations framework convention on climate change and the Kyoto protocol regarding the fulfillment of their quantitative commitments for greenhouse gas emission reduction.

Catalytic abatement of NO and N2O from nitric acid plants: A novel approach using noble metal-modified perovskites

A combined study was achieved to remove sequentially trace amounts of N2O and NO from nitric acid plants. Catalytic systems involving perovskite-type materials have been developed in which precious metals were incorporated in order to compensate deactivation processes for high-temperature N2O decomposition and to enhance the usual low-temperature activity in NO conversion. The high-temperature catalytic decomposition of N2O was studied in the temperature range 500–700°C in realistic conditions with 1000ppm N2O, 5000ppm NO, 6vol.% O2, and 15% H2O. Starting from LaC0.95Pd0.05O3 prepared by a sol gel route, it was found that appropriate sequential oxidative/reductive pre-activation thermal treatments can lead to the diffusion and the segregation of PdOx clusters in strong interaction with the perovskite structure. A sharp increase in intrinsic rates and an apparent compensation effect emphasize the importance of the PdOx-support interface where Pd at the vicinity of anionic oxygen species from the perovskite can facilitate the formation of anionic vacancies potentially active for N2O dissociation. Regarding the NO/H2 reaction, Pt supported on LaFeO3 shows remarkable activities below 100°C depending on the temperature of the pre-reductive thermal treatment and the aging process at 500°C in reaction conditions. Activity in NO reduction at 80°C has been explained from the involvement of the Pt–LaFeO3 interface supported by HRTEM observations relative to the growth of epitaxially orientated Pt particles and the correlation observed between calculated rates based on the length of the interfacial perimeter increasing with the particle size diameter. Such a trend persists at higher temperature (T=255°C) when dPt>7.5nm. On the other hand, for Pt particles with dPt<7.5nm, the NO/H2 reaction becomes more structure sensitive.

Acid-treated vermiculites as effective catalysts of high-temperature N2O decomposition

Vermiculites treated with solutions of HNO3, HCl and H2SO4 were tested in the role of catalysts for high-temperature decomposition of N2O to N2 and O2. Acid treatment of clay mineral resulted in a partial leaching of components of its octahedral sheets, which were partially deposited on the surface of vermiculite. Such modification of the clay samples significantly increased their specific surface area and porosity as well as influenced their surface acidity. Acid treatment of vermiculites activated them in the process of high-temperature N2O decomposition, however activation effect depended on type of acid used as well as duration of acid modification.

La–Fe–O/CeO2 Based Composites as the Catalysts for High Temperature N2O Decomposition and CH4 Combustion

Several composites were prepared by mechanochemical activation of the mixture of well-crystallized LaFeO3 and CeO2 (La:Ce = 0.1, 0.8), including following calcination at 900 °C, and characterized by means of XRD, XPS, HRTEM, EDX and UV–Vis DRS. Their tests as catalysts for N2O decomposition and CH4 oxidation at 700–900 °C showed non-additively high activity of calcined composites in both reactions. 16O/18O exchange was performed at 800 °C in LaFeO3, CeO2 and two composites (both calcined and non-calcined, La:Ce = 0.1) representing mainly unmodified CeO2 core covered by the finely dispersed LaFeO3, La and Fe oxides penetrating near surface layers of fluorite lattice. Namely calcined composite revealed the highest rate of oxygen transfer in the two-phase system “O 2 gas –surface–catalyst bulk” due to prominent increase of the rate of heteroexchange on the modified CeO2 surface at keeping unchanged the highest bulk oxygen mobility characterizing CeO2 that explained its activity in the reactions with oxygen participation.

Effect of surface decoration with LaSrFeO4 on oxygen mobility and catalytic activity of La0.4Sr0.6FeO3−δ in high-temperature N2O decomposition, methane combustion and ammonia oxidation

This article is an attempt to elucidate the role of lattice oxygen mobility in catalytic activity of Sr-substituted ferrites at high temperatures. For this goal, three catalysts with close element (La, Sr, Fe) content but different phases and surface compositions: LaSrFeO4(surface)–La0.4Sr0.6FeO3 (LSF-N), La0.15Sr0.85FeO3–La0.7Sr0.3FeO3 (LSF-C) and LaSrFeO4 have been studied in high temperature reactions of N2O decomposition, ammonia oxidation and methane combustion. The kinetics of 18O/16O oxygen exchange have been analyzed at 800°C and 0.005atm oxygen partial pressure, which is closely corresponding to the reaction conditions, and the rates of surface oxygen exchange and the coefficient of lattice oxygen diffusion have been evaluated. It allowed us to reveal the direct correlation between the surface exchange rate constant and the rate of N2O decomposition. For NH3 oxidation, evidence of the same order of the samples activity both in surface oxygen exchange and ammonia oxidation reaction was shown. In methane oxidation it was found that activity correlates with the rate of exchange for 20 monolayers of oxygen atoms indicating the growing influence of lattice oxygen mobility. The results show that improvement of catalytic properties can be achieved when synthesizing “LaSrFeO4(surface)–La0.4Sr0.6FeO3” composites. Such composites exhibit increased rate of surface oxygen exchange on retention of high lattice oxygen mobility, which can be attributed to formation of heterostructured interfaces.

The influence of modifiers on the activity of Fe2O3 catalyst for high temperature N2O decomposition (HT-deN2O)

The Fe2O3-based catalysts have numerous advantages for HT-deN2O process applications. The possibility of enhancing their activity by various metal oxide modifiers addition (Al, Zr, Ce, La, Cu, Cr) has been investigated. The catalysts were prepared by the coprecipitation method and their physicochemical properties were characterized by N2 sorption, XRF and XRD methods. A quartz gradientless reactor was used for activity evaluation at the temperature range of 500–900°C. The modifiers efficiency was compared and the activity of hematite catalysts at 800̊C was found to increase in the following order: Cr<Ce<Zr<La<Al<Cu.

Insights into the Reactivity of La1−x Sr x MnO3 (x = 0 ÷ 0.7) in High Temperature N2O Decomposition

In this paper a wide range of La1−x Sr x MnO3 (x = 0–0.7) perovskites was synthesized by Pechini route, characterized by XRD (including high temperature measurements), XPS, differential dissolution phase analysis, TPR H2, oxygen exchange and tested in N2O decomposition at 900 °C. At low degree of Sr substitution for La (x ≤ 0.3), high catalytic activity was found for perovskites with hexagonal structure (x = 0.1–0.2) and can be related to fast oxygen mobility caused by the lattice disordering during polymorphic phase transition from the hexagonal to cubic structure. For multiphase samples (x > 0.3) increase of activity and oxygen mobility can be attributed to the formation of the layer-structured perovskite–LaSrMnO4 on the surface. Catalytic activity of La–Sr–Mn–O samples in high-temperature N2O decomposition is discussed with emphasis on its relation to oxygen mobility, surface composition and microstructure of the catalyst particles.