Rate Of N2O Decomposition Research Articles

Preparation of Denitrification Materials with Nickel Slag for Nitric Oxide Decomposition in Cement Kilns.

NOx emission from the cement industry have received much attention. In order to reduce the NOx emission in cement kilns, nickel slag was used to prepare the non-ammonia denitrification material, and a denitrification mechanism was proposed in this study. The results showed that the denitrification material prepared at pH 7 exhibited the best denitrification performance. At low temperature, the highest denitrification performance was achieved between 200 and 300 °C with a NO decomposition rate of approximately 40%. Then, the NO decomposition rate increased as the temperature increased, reaching over 95% above 700 °C. The physicochemical characteristics showed that the material had the highest specific surface area and the highest relative Fe content, which benefited the denitrification performance. The divalent iron of the denitrification material was considered the active site for the reaction, and trivalent iron was not conducive to denitrification performance at a low temperature range. After the denitrification reaction, the Fe3+/Fe2+ increased from 0.89 to 1.31. The proposed denitrification mechanism was the redox process between divalent iron and trivalent iron. This study not only recycles industrial waste to reduce solid waste pollution but also efficiently removes nitrogen oxides from cement kilns without ammonia.

Effect of Silica-Alumina Ratio of Catalysts on NO Decomposition Rate in Cement Kiln Exhaust

In order to deal with the pollution of NO in cement kiln exhaust, the study of NO catalytic decomposition catalyst obtained much more attention. The effect of silica-alumina ratio on NO decomposition rate in cement kiln without other reductant was studied. The NO decomposition rate of catalysts with different silica-alumina ratio was determined by infrared spectrometer. And pore structures and the microstructure of the catalyst were characterized separately by BET surface area, nitrogen adsorption-desorption and XRD. The results show that silica-alumina ratio of catalyst was preferred to be 50 with the best NO decomposition rate when the temperature was below 300 °C. The catalyst with silica-alumina ratio of 60 has the higher catalytic activity when the temperature was higher than 300 °C, and the decomposition rate achieved 70% at 600 °C. XRD results shows the crystallinity of catalysts increased as the silica-alumina ratio increased. BET surface area and the cumulative pore volume of catalysts gradually increased, and the average pore diameter gradually reduced with the increase of silica-alumina ratio.

Preparation of Cu-Al/SiO2 Porous Material and Its Effect on NO Decomposition in a Cement Kiln

Nitrogen oxide (NOx) emissions have attracted much attention for increasing concern on the quality of the atmospheric environment. In view of NO decomposition in the cement production process, the preparation of Cu-Al/SiO2 porous material and its effect on NO decomposition were studied, and the denitrification mechanism was proposed in this paper. The NO decomposition performance of the Cu-Al/SiO2 porous material was tested via the experimental setup and infrared spectrometer and micro gas chromatography (GC). The result shows that the Cu-Al/SiO2 porous material with the template of cetyltrimethylammonium bromide (CTAB) had a better NO decomposition rate than materials with other templates when the temperature was above 500 °C, and NO decomposition rate could approach 100% at high temperatures above 750 °C. Structure analysis indicates that the prepared Cu-Al/SiO2 material structure was a mesoporous structure. The X-Ray Diffraction (XRD) and Ultraviolet–visible spectrophotometry (UV–Vis) results of the denitrification product show that the Cu-Al/SiO2 material mainly decomposed to Cu2O and Si2O, and the CuO decomposed to Cu2O and O2 at high temperature. The Cu(I)O was considered as the active phase. The redox process between Cu(II)O and Cu(I)O was thought to be the denitrification mechanism of the Cu-Al/SiO2 porous material.

Modular Testing of Dinitrogen Oxide (Nitrogen Hemioxide) Catalytic Decomposition Technology for Off-Gas Cleanup Systems for Brest Spent Nuclear Nitride Fuel Reprocessing

Dinitrogen oxide N2O (nitrogen hemioxide) is one of the harmful components of the off-gases during the reprocessing of spent nitride fuel. It enters the gas phase during the dissolution of nitride fuel in nitric acid and denitration of high-activity raffinate or the bottom solution from the evaporation of intermediate-level wastes. The preferred method of neutralizing it is high-temperature catalytic decomposition. Compositions based on γ-aluminum oxide coated with catalysts were found previously. One of the compositions was checked on a semi-industrial setup. The efficiency of N2O decomposition was studied as a function of temperature. It was established that almost complete decomposition occurs at 465–480°C. The specific rate of N2O decomposition at 425–480°C was found as a function of the initial concentration. It is shown that for constant initial concentration of N2O the specific decomposition rate is almost the same in the investigated temperature interval.

Balance between Reducibility and N2O Adsorption Capacity for the N2O Decomposition: CuxCoy Catalysts as an Example.

CuxCoy (CuO-Co3O4 mixed oxides) catalysts were prepared via co-precipitation for the N2O decomposition reaction. They exhibited a higher N2O decomposition activity than that of pure CuO and Co3O4 because of the balance of the redox property and N2O adsorption capacity. Co3O4 presented a large number of surface oxygen vacancies, increasing the N2O chemical adsorption as "□-Co-ON2" on the catalyst surface, whereas CuO was dispersed around Co3O4 and presented high reducibility on the interface of Co3O4-CuOx for the N-O break of N2O, healing oxygen vacancies by leaving one oxygen atom in the vacancy. Based on kinetic studies, the rate constant of N2O decomposition was related to the number of surface vacancy sites ([Mn+]) and the rate of N-O break (k3), whereas the rate-determining step is the N-O break. Therefore, the N2O decomposition rate is first order to the N2O concentration. Overall, both the density functional theory calculations and kinetic results indicate that the quantities of adsorption and activation sites derived from the interaction between Co and Cu (dual-function mechanism) were accounted for the excellent N2O decomposition performance of CuxCoy catalysts.

Influence of Catalysts with Different Templates on Direct Decomposition of NO in Cement Kiln Exhaust

The influence of catalysts with different templates on direct decomposition of NO in cement kiln exhaust was studied in this paper. The NO direct decomposition rate of porous catalyst materials with different templates was determined by infrared spectrometer. And pore structure and the microstructure of the catalysts were characterized by BET surface area, nitrogen adsorption-desorption. The results show that the catalytic performance of porous catalyst without any template is better than catalysts with other templates at low temperature. When the temperature reached 550 °C, NO decomposition rate of porous catalyst with CTAB could reach to more than 80%. And meanwhile, the catalysts with organic template reagent have higher BET surface area than those with inorganic template agent. With the increasing of the reaction time, the NO decomposition rate decreases. After reaction for 3 hours, the decomposition rate decreases from 80% to 40%.

Cobalt oxide catalysts supported on CeO2–TiO2 for ethanol oxidation and N2O decomposition

Cobalt oxide catalysts deposited on titania–ceria supports were examined in deep ethanol oxidation and N2O decomposition. Supports with various molar ratio of CeO2/TiO2 were prepared by the sol–gel method and cobalt components were introduced by impregnation and subsequent calcination. The supports and catalysts were examined by chemical analysis, X-ray diffraction, nitrogen physisorption, H2-TPR, and NH3-TPD. It was found out that the ethanol conversion at 200 °C is proportional to the CeO2/(CeO2 + TiO2) molar ratio in the supports, and temperature T 50 of ethanol oxidation is proportional to the amount of components reducible in the temperature range of 20–500 °C. A comparison of specific catalytic activities in both ethanol oxidation and N2O decomposition proved a lower rate of N2O decomposition than that of oxidation of ethanol (approximately 25 times). The findings confirmed the great importance of the supports surface areas on specific activity of cobalt catalysts in both reactions. The obtained results showed that ceria is the best support of cobalt oxides for both deep ethanol oxidation and N2O decomposition when reaction rates are related to unit amount of active component in the catalysts.

Theoretical modeling of NO electrochemical reduction on multifunctional layer electrode by alternating/direct current electrolysis

A one-dimensional symmetric model on NO electrochemical reduction in solid oxide electrolysis cell(SOEC) considering gas transport, electronic conduction, ionic conduction, and electrochemical process based on multifunctional layer electrode is developed. The simulation results agree well with the experimental results both in the direct current(DC) and alternative current(AC) electrolysis. The distributions of the NO concentration in the electrode are predicted in both DC and AC electrolysis. The effects of temperature, voltage, and O2 concentration were investigated on NO alternative current electrolysis and direct current electrolysis processes. The modeling results show that the optimal frequency of 0.3Hz is corresponded to the maximum NO decomposition rate in different temperatures and voltages. The NO decomposition increases with increasing temperature and decreasing O2 concentration in most cases. At 450°C, the NO decomposition presents first increased and then decreased trend with different voltages at the frequency of 0.3Hz. This is similar to the effects of O2 concentration at 450°C and 475°C at the same frequency.

Catalytic performance of different types of iron zeolites in N2O decomposition

A series of Fe/zeolites (ZSM-35, ZSM-5, beta, and mordenite) samples with Fe/Al molar ratios of 0.33 were prepared using a solid-state ion-exchange method. A combination of ultraviolet-visible diffuse reflectance, in-situ Fourier-transform infrared, and in-situ visible Raman spectroscopic techniques, with a transient response method, was used to investigate the influence of the zeolite framework on the catalytic properties of the Fe/zeolites in N2O decomposition. The results show that the catalytic activity of the Fe/zeolites-HT (HT denotes high-temperature treatment) samples is in the order Fe/ZSM-35-HT > Fe/beta-HT > Fe/ZSM-5-HT > Fe/mordenite-HT. There is a linear relationship between the rate of N2O decomposition and the concentration of binuclear iron sites. This indicates that binuclear iron sites are the active sites for N2O decomposition. A correlation between the formation of binuclear iron sites and Fe ion distribution among the cationic sites is proposed. Two Fe(II) cations located in two adjacent six-membered rings in a 10-membered ring channel (α sites) or in two neighboring six-membered rings in an eight-membered ring channel (β sites) of Fe/ZSM-35 are favorable for the formation of active binuclear iron sites. Similar structure can also be formed in two adjacent six-membered rings in polymorphs A and B of beta zeolite or in the six-membered rings at the intersection of the straight and sinusoidal channels of the ZSM-5 framework. For the Fe/mordenite-HT sample, most of the iron species are present as isolated iron cations, so it has the lowest activity in N2O decomposition.

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.

Comparative study on the direct decomposition of nitrous oxide over M (Fe, Co, Cu)–BEA zeolites

Catalytic activities of M (Fe, Cu, Co)–beta (BEA) zeolites for N2O direct decomposition were systematically investigated by employing both experimental and theoretical [density functional theory (DFT)] approaches. The activities of M–BEA determined by intrinsic kinetic evaluations are in good agreement with the DFT calculations and the microkinetic analyses, revealing that the distinguishing activities of M–BEA were mainly attributed to their distinct energy barriers for the O2 desorption (Part 3). During the DFT calculations, a unique intermediate (IM) was generated only over Co–BEA, which was verified by the activity evaluation and N2O-TPD experiments, showing that the formation of IM reduced N2O decomposition rate of Co–BEA. The negative effect of the IM was thereafter investigated by the microkinetic analyses through which it was known that the second forward reaction rate constant of Co–BEA was lower than its reverse reaction rate constant, resulting in a final decline of the N2O decomposition rate.

Role of active oxygen and NOx species in N2O decomposition over Fe-ferrierite

Direct evidence for the formation of surface Fe–NOx species over iron ferrierites during decomposition of N2O was found with a combination of temperature-programmed desorption of adsorbed surface species and infrared and Mössbauer spectroscopies. Surface NOx species were produced via the conversion of a transiently formed Fe(III)–O by exposing iron ferrierites (Si/Al=8.7, Fe/Al=0.07–0.1) to N2O. The transformation of Fe(III)–O into Fe–NOx was time- and temperature- dependent. Below 280°C, predominantly Fe(III)–O species were formed; these species are known to be highly active in oxidations at low temperatures. A transformation of Fe(III)–O into Fe–NOx species occurred when the reaction temperature was increased or when the reaction time was increased at low temperatures. This resulted in the disappearance of the oxidation activity of iron ferrierite. In contrast, the formation of Fe–NOx species enhanced the rate of N2O decomposition. Once formed, NOx species were stable during the subsequent N2O decomposition.

A study on effect of Rh precursor and La addition on N2O decomposition over Rh catalyst

The decomposition of N2O in the presence of oxygen was studied on Rh/CeO2 and Rh/La2O3–CeO2 catalysts prepared by wet impregnation method. The conversion of N2O decomposition increased as the Rh loading increased, and the Rh-chloride catalyst showed a poor activity than the Rh-nitrate catalyst. XPS and IC/ICP analysis confirmed that the Rh-chloride catalyst's low activity caused since Rh-chloride catalyst had the some RhCl3 species. N2O decomposition rate over Rh/La2O3–CeO2 catalysts decreased as the La loading increased due to the SMSI effect between Rh and CeO2. H2 TPR confirmed that the activity and reducibility of the catalyst were closely related.

Effect of temperature and concentration on treating NO in simulated diesel exhaust via SOFCs with Cu-added (LaSr)MnO 3 cathode

A solid oxide fuel cell unit is constructed with Ni–YSZ as the anode, YSZ as the electrolyte, and Cu-added La 0.8Sr 0.2MnO 3–Ce 0.9Gd 0.1O 1.95 as the cathode. Cu addition is done by impregnation and doping, respectively. It is found that zero NO x emissions can be achieved no matter how large the inlet NO concentration is in the simulated diesel exhaust. The major driving force for NO x conversion is not the electrical power. Cu addition by impregnation results in larger rate of NO decomposition than that by doping. At 600 °C, both NO and NO x conversions increase with increasing O 2 concentration from 6 to 14%. Lower temperature is beneficial for the NO x conversion. Both very low and very high NO concentrations are beneficial for the NO and NO x conversions.

Mechanism and micro-kinetics of direct N2O decomposition over BaFeAl11O19 hexaaluminate and comparison with Fe-MFI zeolites

Mechanistic and kinetic aspects of direct N2O decomposition over BaFeAl11O19 hexaaluminate were investigated in the Temporal Analysis of Products (TAP) reactor and compared with those previously determined for Fe-MFI zeolites. The catalysts were chosen due to their de-N2O operation in significantly different temperature regimes. Several micro-kinetic models were evaluated for describing the transient responses of N2O, N2, and O2 obtained in N2O pulse experiments at 823–973K. Thorough discrimination between these models enabled us to conclude that the preferred models of N2O decomposition over BaFeAl11O19 and Fe-MFI zeolites differ in the reaction pathways leading to O2 and N2. Gas-phase N2 and O2 are simultaneously formed over BaFeAl11O19 upon interaction of gas-phase N2O with a bi-atomic surface oxygen (*–O2) species. Contrarily, the formation of O2 over Fe-MFI occurs via a sequence of three elementary heterogeneous steps and limits the overall rate of N2O decomposition. Despite the easy O2 formation, BaFeAl11O19 is less active for N2O decomposition below 973K than the Fe-MFI zeolites due to the low coverage by *–O2. According to our quantitative micro-kinetic analysis, this species is formed when gas-phase N2O reacts with a mono-atomic oxygen (*–O) species. This reaction pathway is strongly influenced by the degree of isolation of iron species. The higher the degree of iron isolation in the catalyst, the lower the de-N2O activity.

Direct Decomposition of NO into N2 and O2 on SrFe0.7Mg0.3O3 Perovskite Oxide

Abstract NO direct decomposition on doped SrFeO3 perovskite oxide was investigated. The ability of SrFeO3 for direct decomposition of NO is strongly affected by the dopant in Fe sites. Among the examined dopants and compositions, the highest yield of N2 was achieved on SrFe0.7Mg0.3O3. When SrFe0.7Mg0.3O3 was loaded with Pt, the N2 yield further improved, and the light-off temperature fell by 100 K. On this catalyst, the yields of N2 and O2 were 56 and 35%, respectively, at 1123 K. On the Pt-loaded SrFe0.7Mg0.3O3 catalyst, the NO decomposition rate increased with increase in the NO partial pressure with PNO1.31. The presence of oxygen slightly decreased the N2 yield with PO2−0.12. Therefore, the effect of oxygen poisoning on NO decomposition upon Pt-loaded SrFe0.7Mg0.3O3 is small. From the result of O2-TPD, Pt loading possibly weakens the adsorption strength of surface oxygen and enhances NO adsorption. In summary, this study shows that the substitution of Fe with lower valence cation in SrFeO3 and also loading a small amount of Pt are highly effective for increasing the NO decomposition activity.

Direct decomposition of NO into N2 and O2 on BaMnO3-based perovskite oxides

Effects of dopant in BaMnO3 perovskite oxide on the NO direct decomposition activity were investigated. NO direct decomposition activity was greatly elevated by doping La and Mg for Ba and Mn site in BaMnO3, respectively. The highest N2 yield was achieved on Ba0.8La0.2Mn0.8Mg0.2O3. The NO decomposition rate increased with increasing NO partial pressure with PNO1.19. Coexistence of oxygen lowered the N2 yield with PO2−0.18; however, N2 yield of 40% was sustained even under coexisting of 5% O2 at 1123K. Adsorption state of oxygen was also studied with temperature programmed desorption (TPD) method and the desorption temperature of oxygen was lowered by doping Mg for Mn site in BaMnO3.

Catalytic reduction of N2O by H2 over well-characterized Pt surfaces

A 0.65% Pt/SiO2 catalyst has been prepared using an ion exchange technique and extensively characterized prior to being used for continuous catalytic N2O reduction by H2 at very low temperatures, such as 363 K. The supported Pt with a high dispersion of 92% gave no presence of O atoms remaining on an H-covered Pts, based on in situ DRIFTS spectra of CO adsorbed on Pts after either N2O decomposition at 363 K or subsequent exposure to H2 for more than 1 h; thus the residual uptake gravimetrically observed even after the hydrogen titration on an O-covered surface is associated with H2O produced by introducing H2 at 363 K onto the oxidized Pts. Dissociative N2O adsorption at 363 K on Pts was not inhibited by the H2O(ad) on the silica surface but not on Pts, as acquired by IR peaks at 3,437 and 1,641 cm−1, in very consistent with the same hydrogen coverage, established via H2-N2O titration on a reduced Pts, as that revealed upon the titration reaction with a fully wet surface on which all bands and their position in IR spectra for CO are very similar to that obtained after H2 titration on a reduced Pts. Based on the characterization using chemisorption and in situ DRIFTS and TPD measurements, the complete loss in the rate of N2O decomposition at 363 K after a certain on-stream hour, depending significantly on N2O concentrations used, is due to self-poisoning by the strong chemisorption of O atoms on Pts, while the presence of H2 as a reductant could readily catalyze continuous N2O reduction at 363 K that is a greatly lower temperature than that reported earlier in the literature.

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.

Kinetics and mechanism of NO decomposition over La 0.4Sr 0.6Mn 0.8Ni 0.2O 3 perovskite-type oxides

Perovskite-type oxide La 0.4Sr .6Mn 0.8Ni 0.2O 3 showed high activity for NO decomposition and thus was taken as the catalyst for investigation. Based on the ‘recycle’ mechanism of NO decomposition (NO 2 acts as an intermediate of O 2 formation) we reported recently, the kinetics of NO decomposition over La 0.4Sr .6Mn 0.8Ni 0.2O 3 was investigated. The NO decomposition rate was practically first-order for NO in the range 0.5–2.0 vol.% NO/He, while the reaction order varied from −0.24 to −0.08 for O 2 (0–6 vol.% O 2/He), depending on the temperature. The kinetics deduced from the ‘recycle’ mechanism accords well with that observed in practice by introducing the item K −6 ( K −7) 1/2 P NO ( P O 2 ) 1/2, which reflects the reciprocity of O 2 and NO in the reaction and is introduced in the kinetics for the first time. The rates and NO 2 dissociation equilibrium constants calculated from the practical reaction certified that NO 2 dissociation is indeed an important step of NO decomposition, and hence suggested that the ‘recycle’ mechanism is believable.