N2O Decomposition Research Articles

The effect of inert gases (Xe, Ar, Ne, He) on decomposition reactions of N2O, CH4 and CO2 at high pressures

In a pulsed compression reactor (PCR) experiments were done with N2O (4%mol), CH4 (1%mol) and CO2 (2%mol) diluted in the inert gases Xe, Ar, Ne and He. The mixtures were compressed up to 250 bar, reaching temperatures of up to 4000 K. At equal temperature, pressure and volume, significant differences (up to 20%) were measured in the conversion of the three species in different noble gases. The measurements with N2O decomposition showed that the reaction is the fastest in the most heavy noble gas tested. The conversion decreased as the molar mass of the noble gas decreased. Likewise, methane pyrolysis was measured to be the fastest in xenon and slowed down in accordance with the mass of the inert molecule. A reverse trend was measured for the decomposition of CO2 to CO and O⋅, which is explained by the dominant role of the reverse reaction. As a result, the CO2 data is also explained by conversion rates that are higher in heavier gases. This paper provides a first attempt to understand the observed influence of the molar mass of the inert bathing gas on the reaction rate in the high pressure domain. A theory is proposed based on a Newtonian description of reactant activation by the inert bathing gas.

Multiple cobalt species on HZSM-5 cooperative catalyzing N2O decomposition

As a strong greenhouse gas with a wide lifespan, nitrous oxide (N2O) reduction emissions are imperative. Transition metal oxides, especially cobalt oxides, possess superior N2O catalytic decomposition properties. A series of cobalt-incorporated HZSM-5 (Co/HZ) catalysts were synthesized by citric acid-complexion impregnation and were systematically investigated by N2O decomposition and characterizations. Co content and calcination temperature influenced cobalt species distribution and active site amount. Multiple cobalt species were found and cooperatively catalyzed N2O decomposition. Co2+ ions in cobalt species are regarded as active sites in N2O decomposition and the 10Co/HZ-800 catalyst showed better N2O catalytic decomposition performance, O2, and NO tolerance. The 10Co/HZ-800 catalyst was subjected to in situ diffuse reflectance infrared Fourier-transform spectroscopy (in situ DRIFTS) for surveying N2O adsorption patterns on the surface under different temperatures and atmospheres.

Broadband ultrafast-laser-absorption measurements of NO[formula omitted] absorption cross-sections from 430 to 500 nm at high temperatures behind shock waves

This work presents broadband spectrally resolved measurements of the absorption cross-section of NO2 from approximately 430 to 500 or 580 nm, depending on temperature, with a spectral resolution of approximately 0.06 nm. An ultrafast-laser-absorption-spectroscopy (ULAS) diagnostic was developed and used to provide broadband (up to approximately 900 cm−1 per laser shot) cross-section measurements with sub-nanosecond time resolution. Cross-section measurements were acquired from 430 to 580 nm in a heated gas cell at temperatures of 296 K and 670 K and a pressure of 1.5 bar. Cross-section measurements were also acquired behind reflected shock waves at temperatures near 970 K, 1150 K, and 1450 K at pressures near 1.5 bar. A quantum-cascade-laser-absorption diagnostic for NO was used to measure NO mole fraction at 500 kHz and determine the extent of NO2 decomposition in shock-tube experiments. The measured cross-sections typically exhibit good agreement with prior measurements available at select wavelengths and conditions as well as with recently developed theoretical predictions at most wavelengths and temperatures studied. A detailed description of the experimental and data processing procedures that enabled the ULAS measurements despite pronounced variations in laser pulse energy and the absence of non-resonant wavelengths within the pulse bandwidth are also presented.

Co-existence of atomically dispersed Ru and Ce3+ sites is responsible for excellent low temperature N2O reduction activity of Ru/CeO2

Nitrous oxide N2O reduction is a big challenge due to high global warming potential of N2O. (∼300 times higher compared with CO2). The best known catalysts, such as Rh/ceria, require relatively high temperatures for N2O decomposition. Herein, we report that Ru/ceria catalysts with low Ru loading of ∼0.25 wt% efficiently catalyze low temperature N2O reduction by CO starting at 100 ℃ (full N2O conversion below 200 ℃) under industrially relevant flow rates and gas concentrations. This remarkable performance stems from maintaining isolated Ru cations even on reduced ceria surface and, simultaneously, the propensity of Ru to affect ceria surface to form labile surface oxygen thereby creating large number of oxygen vacancies (Ce3+ cations) in the presence of CO. In contrast, for Rh/CeO2 catalysts with equivalent metal loading, the activity is much lower because atomically dispersed Rh sinters into metallic clusters at the onset reaction temperature (∼200 °C): these clusters are much less effective than isolated single Ru ions, with lower Ce3+ concentration maintained on reduced Rh/CeO2 catalyst. Our study highlights the benefits of gaining molecular-level insight into the dynamic nature of catalytically active sites under reaction conditions for preparing catalysts containing low loading of precious metals with unsurpassed low temperature activity.

Investigation of the decomposition mechanism of MTNP melt-cast explosive at different temperatures and pressures through ReaxFF/lg molecular dynamics simulations.

Thermal decomposition of 1-methyl-3,4,5-trinitropyrazole (MTNP), a melt-cast explosive, was investigated at different temperatures (2500, 2750, 3000, 3250, and 3500 K) and pressures (3000 K/0.5 GPa, 3000 K/1 GPa) using the ReaxFF/lg force field. The study aimed to analyze the changes in reactant quantities, initial reaction pathways, and final product yields. The results demonstrated that complete decomposition of MTNP molecules occurred within a timeframe of 200 ps, with shorter decomposition times observed as the temperature increased. The high-temperature thermal decomposition of MTNP was found to follow two primary reaction pathways. Reaction 1 involved denitration, while reaction 2 proceeded with nitro group isomerization. DFT calculations indicated that nitro group isomerization was the most favorable reaction. During the initial stages, higher quantities of NO2, NO, and N2 were observed compared to other species. This can be attributed to the relatively higher nitrogen and oxygen content in the MTNP structure. Among the five reaction temperatures, it was observed that the quantities of small molecules followed the order of NO2 > NO > N2 > CO. Moreover, with increasing temperature, the quantities of all four small molecules increased, indicating that higher temperatures promoted the progression of the reactions. However, as the pressure increased, there was a trend of initially increasing and then decreasing to zero for the quantities of NO2 and NO. This suggests that high temperature accelerated the high-temperature thermal decomposition of NO2 and NO, leading to a significant increase in the content of N2. A 3 × 5 × 5 supercell model of MTNP was constructed in Materials Studio, consisting of 75 unit cells and 300 MTNP molecules. The model was then subjected to a 20 ps geometric optimization using the Polak-Ribiere version of the conjugate gradient (CG) algorithm in the large-scale atomic/molecular massively parallel simulator (LAMMPS) under the isothermal-isobaric (NPT) ensemble at 1 atm pressure and 300 K temperature. Following the optimization, molecular dynamics simulations were performed on the model at five temperatures (2500, 2750, 3000, 3200, and 3500 K) under 1 atm using the NPT ensemble for a total duration of 1 ns. During the simulations, atomic trajectories, as well as information on atomic and molecular species, were output every 500 steps. Subsequently, a custom script was utilized to analyze the thermal decomposition pathways and products. A time step of 0.1 fs was employed for the calculations, and periodic boundary conditions were applied to eliminate boundary effects.

An Experimental and Density Functional Theory Simulation Study of NO Reduction Mechanisms over Fe0 Supported on Graphene with and without CO.

NO reduction over highly dispersed zerovalent iron (Fe0) supported on graphene (G), with and without the presence of CO in the reacting stream, was systematically studied using a fixed-bed reactor, and the reaction mechanism was examined with the aid of in situ Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. The in situ FTIR results showed that NO adsorbed on the Fe0 site is reduced to form active surface oxygen species (O*), which is then reduced by carbon in graphene to form CO2. The presence of CO in the reacting stream helps to reduce the oxidized Fe(O) sites to regenerate Fe0 sites, making NO reduction easier. It was revealed that NO and CO2 are easily adsorbed on the active surface oxygen species (O*) to form nitrate and carbonate, inhibiting their reduction by CO and deactivating the catalyst. The DFT calculations results suggest that the role of Fe is to reduce the energy barrier of the NO adsorption and decomposition, which controls the formation of active surface oxygen species and N2. The combined FTIR and DFT results offer new insights into the possible mechanism of catalytic NO reduction over graphene loaded with Fe, with and without CO.

Cascade NH3 Oxidation and N2O Decomposition via Bifunctional Co and Cu Catalysts.

The selective catalytic oxidation of NH3 (NH3-SCO) to N2 is an important reaction for the treatment of diesel engine exhaust. Co3O4 has the highest activity among non-noble metals but suffers from N2O release. Such N2O emissions have recently been regulated due to having a 300× higher greenhouse gas effect than CO2. Here, we design CuO-supported Co3O4 as a cascade catalyst for the selective oxidation of NH3 to N2. The NH3-SCO reaction on CuO-Co3O4 follows a de-N2O pathway. Co3O4 activates gaseous oxygen to form N2O. The high redox property of the CuO-Co3O4 interface promotes the breaking of the N-O bond in N2O to form N2. The addition of CuO-Co3O4 to the Pt-Al2O3 catalyst reduces the full NH3 conversion temperature by 50 K and improves the N2 selectivity by 20%. These findings provide a promising strategy for reducing N2O emissions and will contribute to the rational design and development of non-noble metal catalysts.

Fe-MOR and Fe-FER as catalysts for abatement of N2O with CH4: in situ UV–vis DRS and operando FTIR study

The catalytic reduction of N2O with CH4 in absence or in presence of O2 (CRN2O or SCRN2O) and H2O (hydrothermal conditions) was studied on Fe-MOR and Fe-FER catalysts with similar Al distribution and iron-loading. In N2O decomposition and SCRN2O Fe-FER catalysts were more active than Fe-MOR, whereas in CRN2O the catalysts exhibited similar activity. In situ FTIR and UV–vis spectroscopies of thermally activated catalysts revealed that Fe(II) species are better stabilized in FER than in MOR topology. In the presence of CH4, Fe(III)-oxo species were reduced to Fe(II) in both zeolites and became active sites for the CRN2O process. In SCRN2O the presence of O2 decreased the activity of Fe-MOR due to a partial re-oxidation of the active sites. The addition of H2O to the feed caused a poor and reversible deactivation. Operando FTIR experiments provided insights into the reaction pathways and suggested formaldehyde and formate surface species as intermediates.

Retracted: Clinical Significance and Correlation Decomposition of Cord Blood NO, Activin A Levels, and MCA/UA with Fetal Distress.

[This retracts the article DOI: 10.1155/2022/2693776.].

On the optimal Cs/Co ratio responsible for the N2O decomposition activity of the foam supported cobalt oxide catalysts

Structured foam catalysts for N2O decomposition containing Co and Cs were prepared via conventional and organic-assisted impregnation method (acetic acid, citric acid, glycerol, glycine, urea). Organic-assisted impregnation caused higher abundance of smaller particles and different faceting. Glycerol usage leads to increase of specific rate constant for N2O decomposition, urea leads to its decrease. The optimal amount of Cs in Co3O4deposited on the foam was 2–3 times higher than in the bulk Co3O4-Cs due to the dispersion of part of the Cs species over the bare support. The use of glycerol caused a better surface coverage by spinel phase, thus leaving less space for spreading the cesium on the support instead of on the spinel phase. The positive effect of glycerol on the performance of the catalysts with optimized cesium content was attributed to refaceting of the spinal nanocrystals, and greater resistance of the (100) planes to gaseous NO/H2O contaminates.

Identifying and clearing individual oxygen impurities on graphene through the use of NO2 as a radical scavenger

We present a novel method to detect and eliminate oxygen adatoms on a graphene basal plane, which can be observed as individual single-electron transfer (SET) events through graphene Hall measurements. The central idea, supported by first-principles calculations, is to use NO2 as a radical scavenger, effectively targeting and removing oxygen impurities on graphene. The reaction between NO2 and the oxygen adatom produces a negatively charged NO3− species and creates a hole carrier in graphene. Subsequently, NO3− reacts with NO2 to form N2O5, accompanied by an electron back-donation to graphene. The thermal decomposition of N2O5 produces neutral NO3, which can accept an electron from graphene and return to the NO3− state. Under conditions of low oxygen impurity levels and NO2 partial pressures, these SET reactions induce intermittent, step-like changes in the graphene's Hall resistivity ρxy at room temperature. Notably, the simulated ρxy patterns during NO2 adsorption closely resemble previously observed patterns [Schedin et al., Nat. Mater. 6 (2007) 652–655], suggesting a connection to the proposed SET reactions for unintentionally introduced oxygen impurities. Furthermore, we find that NO2 also reacts with hydroxyl and peroxide groups on the graphene basal plane, removing them by forming HNO3 and N2O5, respectively. Our findings offer a promising approach to remove oxygen-containing functional groups from graphene, paving the way for obtaining high-quality graphene from reduced graphene oxide.

Photocatalysis: A Possible Vital Contributor to the Evolution of the Prebiotic Atmosphere and the Warming of the Early Earth

The evolution of the early atmosphere was driven by changes in its chemical composition, which involved the formation of some critical gases. In this study, we demonstrate that nitrous oxide (N2O) can be produced from Miller’s early atmosphere (a mixture of CH4, NH3, H2, and H2O) by way of photocatalysis. Both NH3 and H2O were indispensable for the production of N2O by photocatalysis. Different conditions related to seawater and reaction temperature are also explored. N2O has a strong greenhouse gas effect, which is more able to warm the Earth than other gases and offers a reasonable explanation for the faint young Sun paradox on the early Earth. Moreover, the decomposition of N2O into N2 and O2 can be boosted by soft irradiation, providing a possible and important origin of atmospheric O2 and N2. The occurrence of O2 propelled the evolution of the atmosphere from being fundamentally reducing to oxidizing. This work describes a possible vital contribution of photocatalysis to the evolution of the early atmosphere.

Direct NO decomposition over Rh-supported catalysts for exhaust emission control

Direct nitrogen oxide decomposition (DND) is a promising alternative to the selective catalytic reduction (SCR) of nitrogen oxides for emissions control, as it eliminates the need to inject reductants such as urea/ammonia. The present study investigates the implementation of Rh-supported metal oxides for the DND reaction. Rh supported on each of PrOX, TiO2, Al2O3, and CeO2 were characterized, and we found that initially the catalytic activity on Rh/PrOX and Rh/TiO2 was very high, though it deactivated over time due to strong poisoning by adsorbed oxygen. This deactivation by oxygen poisoning was verified through in-situ DRIFTS, XPS, NEXAFS, O2-TPD measurements and density functional theory (DFT) calculations, respectively. This catalytic deactivation was positively regenerated by reductive treatments with CO or H2. This study discovers the mechanism of DND deactivation and regeneration over Rh-supported metal oxides, which will provide significant insight into further development of DND.

Bipropellant Enabled Solid Oxide Fuel Cell Stack Power Supply: Energy Agility for Space Vehicles

Spacecraft often have instances where they are required to operate for long periods of time with significant power requirements and no access to solar power. While a battery system could be designed to meet these occasional, and possibly unexpected requirements, creating a power supply to meet these infrequent demands results in having a battery system that is excessively large, massive, and inefficient. A Solid Oxide Fuel Cell (SOFC) system capable of running on the same fuel and oxidizer as the onboard thruster of a bipropellant thruster equipped spacecraft can eliminate much of the added mass and volume needed to enable batteries to meet extreme power demands and create more operational flexibility on how the chemical energy in stowed bipropellants are used. If the spacecraft needs thrust, the bipropellant can be ignited to provide thrust. If the spacecraft needs electric power, the spacecraft can consume bipropellant to generate auxiliary power. In this work, the proven bipropellant pair ammonia (NH3) and nitrous oxide (N2O) are shown to be a viable fuel and oxidant for hydrogen (H2) consuming air breathing SOFCs, as spontaneous NH3 decomposition will generate H2 and spontaneous N2O decomposition will generate O2. A scale up to a 5-cell SOFC stack fed NH3 and N2O produced power up to ~89W. Higher power can be achieved by scaling up the number of cells in a stack to achieve required power demands. The results of this study demonstrate the potential and feasibility of integrating SOFCs with a bipropellant thruster to creating a dual functioning spacecraft system that can satisfy operational power requirements and on-orbit maneuverability.This material is based on research sponsored by Air Force Research Laboratory under agreement number FA9453-21-C-0060. The views expressed are those of the authors and do not reflect the official guidance or position of the United States Government, the Department of Defense or of the United States Air Force. Approved for public release; distribution is unlimited. Public Affairs release approval #AFRL20230023. Figure 1

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.

Direct decomposition of N2O over Co3O4/ZrSn1−xFexO4−δ catalysts

This study focuses on the development and characterization of precious-metal-free Co3O4/ZrSn[Formula: see text][Formula: see text]Fe[Formula: see text]O[Formula: see text][Formula: see text] catalysts for the purpose of direct N2O decomposition. The oxygen supply from ZrSn[Formula: see text][Formula: see text]Fe[Formula: see text]O[Formula: see text][Formula: see text] facilitated N2O decomposition. Among the prepared catalysts, the 19 wt.% Co3O4/ZrSn[Formula: see text]Fe[Formula: see text]O[Formula: see text][Formula: see text] catalyst exhibited the highest catalytic activity. Furthermore, N2O was completely decomposed at a relatively low temperature of 500∘C.

Modelling of NO Reduction on CeO2-Supported Pt and Pd Nanoclusters

ABSTRACT The reduction mechanism of NO to N2 on CeO2-supported Pt and Pd nanoclusters (Pt/CeO2 and Pd/CeO2) is analyzed using density functional theory. Different NO decomposition and N2 formation pathways are evaluated, and the thermodynamically preferable paths are identified. The energy barrier of NO decomposition on Pt/CeO2 indicates that the rate of reaction via metallic cluster sites and the ceria oxygen vacancies are comparable. In contrast, the cluster metallic sites of the Pd/CeO2 induce a lower energy barrier of NO decomposition relative to the oxygen CeO2 vacancy sites. The N2 formation on the Pt/CeO2 preferentially occurs via the N–N association, whereas the N2O deoxidation is energetically preferred on the Pd/CeO2.

Re-Examination of the N2O + O Reaction.

The reaction of N2O with O is a key step in consumption of nitrous oxide in thermal processes. It has two product channels, NO + NO (R2) and N2 + O2 (R3). The rate constant for R2 has been measured both in the forward and the reverse direction at elevated temperature and is well established. However, the rate constant for the N2 + O2 channel (R3) has been difficult to quantify and has significant error limits. The direct reaction on the triplet surface has a barrier of around 40 kcal mol-1, and it is too slow for the N2 + O2 channel to have any practical significance. Recently, Pham and Lin (2022) suggested an alternative low activation energy reaction path that involves intersystem crossing and reaction on the singlet surface. In the present work, we re-examined a wide range of experiments relevant for the N2O + O reaction through kinetic modeling, paying attention to the impact of artifacts such as impurities and surface reactions. Experimental results from shock tubes and batch reactors on the final NO yield in N2O decomposition, covering temperatures of 973-2200 K and pressures of 0.013-11.5 atm, support k3 ∼ 0, consistent with the high activation energy for reaction on the triplet surface and a low probability of ISC.

Density functional theory study of N2O decomposition catalyzed by Pd4−/0/+ clusters

Density functional theory study of N2O decomposition catalyzed by Pd4−/0/+ clusters

Wall heat loss effect on the emission characteristics of ammonia swirling flames in a model gas turbine combustor

Ammonia (NH3) combustion is regarded as one of the most promising solutions to realize zero CO2 emission. However, its low reactivity, low heat release result in a strong thermal effect (wall heat loss effect) which significantly affects flame macro structure and NOx emission characteristics. In this study, an air film cooling on the swirling combustion chamber was designed to investigate the wall heat loss effect on NOx emission. The flame structure and NO production were measured with the OH-/NO-PLIF techniques. The NOx emission was analyzed by the Gasmet DX4000 Fourier Transform Infrared (FTIR) gas analyzer. Large eddy simulation was also conducted with detailed chemistry to extend the understanding of the experimental findings. For the current combustion chamber, a larger convection heat loss was obtained when increasing the cooling air flow rate. NO emission shows a decreasing trend with heat loss which is mainly caused by the chemical reactions at near all region. This can be verified by the relatively farther NO profile from the combustor wall. By analyzing the LES results at near all region, the combustion efficiency is decreased due the lower temperature. As a result, NO production from HNO and NH pathway is suppressed due to the local OH decreasing in near-wall region. The larger unburned NH3 in the exhausted gas may also consumes NO by the NO reduction reactions. In comparison, N2O, around 300 times global warming potential than that of CO2, significantly increases as the heat loss increases. This is mainly because that the production of N2O from NO is promoted and N2O decomposition is suppressed within the thermal boundary. This study suggests that N2O might become a more serious emission component in NH3 fueled gas turbines. Furthermore, the heat loss effect on the NOx production should be fully considered when designing the gas turbine combustion chamber with strong wall cooling.