N2O Decomposition Research Articles

Highly active Mn-VO-Co sites by cobalt doping on cryptomethane for enhanced catalytic decomposition of N2O.

Direct catalytic decomposition has shown great promise in controlling the greenhouse gas N2O. Herein, we synthesize a series of cobalt-doped cryptomethane (OMS-2) catalysts for N2O catalytic decomposition by a mild one-step sol-gel method. The Co0.1-OMS-2 exhibits superior catalytic performance with 90% N2O conversion at 398 °C, which is attributed to the formation of the Mn-VO-Co structure served as active sites. The increased electron density on oxygen vacancies promotes the electron transfer between oxygen vacancies and N2O molecules, in turn facilitating the adsorption and activation of N2O. Moreover, Co doping reduces the formation energy of oxygen vacancies. However, excessive Co doping results in the decrease of highly active Mn-VO-Co sites and the formation of Co3O4, which makes Co0.3-OMS-2 exhibit poor catalytic activity. The DFT calculation illustrates that Langmuir-Hinshelwood is the primary reaction mechanism over Co0.1-OMS-2. This study broadens the materials applicable for the catalytic decomposition of N2O, offering an effective approach to modulate the electronic structure at oxygen vacancies.

Modulation of Co spin state at Co3O4 crystalline-amorphous interfaces for CO oxidation and N2O decomposition

Modulation of electronic spin states in cobalt-based catalysts is an effective strategy for molecule activations. Crystalline-amorphous interfaces often exhibit unique catalytic properties due to disruptions of long-range order and alterations in electronic structure. However, the mechanisms of molecule activation and spin states at interfaces remain elusive. Herein, we present a Co3O4 spinel-based catalyst featuring crystalline-amorphous interfaces. Characterization analyses confirm that tetrahedral Co2+ is selectively etched from bulk spinel, forming amorphous CoO islands on the surface. The resultant symmetry breaking in the coordination field induces a reconstruction of the Co3+3 d orbitals, leading to high-spin states. In CO oxidation, the interface serves as novel active sites with a lower energy barrier, facilitated by lattice oxygen activation. In N2O decomposition, the interface promotes reassociation of dissociated oxygen through quantum spin exchange interactions. This work provides a straightforward approach to modulating the spin state of interfaces and elucidates their role in molecule activations.

Enhanced Nitrous Oxide Decomposition on Zirconium-Supported Rhodium Catalysts by Iridium Augmentation.

The effective elimination of N2O from automobile exhaust at low temperatures poses significant challenges. Compared to other materials, supported RhOx catalysts exhibit high N2O decomposition activities, even in the presence of O2, CO2, and H2O. Metal additives can enhance the low-temperature N2O decomposition activities over supported RhOx catalysts; however, the enhancement mechanism and active sites require further investigation. In this study, we demonstrate the significant enhancement of the low-temperature N2O decomposition activity of a monoclinic ZrO2-supported Rh catalyst [Rh(1)/ZrO2] with Ir addition in the presence of N2O + O2 + CO2 + H2O. The promotional effect of Ir and the active sites on N2O decomposition in Rh(1)-Ir(1)/ZrO2 (Rh = 1 wt % and Ir = 1 wt %) were investigated by kinetic studies and in situ spectroscopic methods, including X-ray absorption spectroscopy, ambient-pressure X-ray photoelectron spectroscopy, and ultraviolet-visible spectroscopy. These results indicate that both surface Rh and Ir species in Rh(1)-Ir(1)/ZrO2 were active sites for N2O catalytic decomposition at low temperatures, and Ir augmentation promoted the desorption of gaseous O2, which are regarded as key steps in N2O decomposition.

A Density Functional Theory (DFT) Modeling Study of NO Reduction by CO over Graphene-Supported Single-Atom Ni Catalysts in the Presence of CO2, SO2, O2, and H2O.

The mechanisms of NO reduction by CO over nitrogen-doped graphene (N-graphene)-supported single-atom Ni catalysts in the presence of O2, H2O, CO2, and SO2 have been studied via density functional theory (DFT) modeling. The catalyst is represented by a single Ni atom bonded to four N atoms on N-graphene. Several alternative reaction pathways, including adsorption of NO on the Ni site, direct reduction of NO by CO, decomposition of NO to N2O followed by reduction of N2O to N2, formation of active oxygen radical O*, and reduction of O* by CO, were hypothesized and the energy barrier corresponding to each of the reaction steps was calculated using DFT. The most probable pathway was found to be that NO adsorbed on the Ni site decomposes via the Langmuir-Hinshelwood mechanism to form N2O and subsequently N2, leaving an active oxygen radical (O*) on the surface, which is then reduced by CO. The large adsorption energy of NO on the Ni site results in strong resistance to CO2, SO2, O2, and water vapor. The activation energy of N2O reduction to N2 was found to be larger than those of NO decomposition to N2O and active oxygen radical reduction by CO, illustrating that the step of N2O reduced to N2 is the rate-controlling step.

Unraveling the O2 resistance of promoters in BaO-Y2O3-based catalyst for NO decomposition

Unraveling the O2 resistance of promoters in BaO-Y2O3-based catalyst for NO decomposition

Recent advances in low-temperature nitrogen oxide reduction: effects of electric field application.

This article presents a review of catalytic processes used at low temperatures to reduce emissions of nitrogen oxides (NOx) and nitrous oxide (N2O), which are exceedingly important in terms of their environmental impacts on the Earth. With conventional purification technologies, it has been difficult to remove these compounds under low-temperature conditions. By applying a catalytic process in an electric field for the three reactions of three-way catalysts (TWC), NOx storage reduction catalysts (NSR), and direct decomposition of N2O, we have achieved high catalytic activity even at low temperatures. By promoting ion migration on the catalyst surface, we have filled in the gaps in conventional catalytic technology and have opened the way to more efficient conversion of NOx and N2O.

A review of chemical kinetic mechanisms and after-treatment of amino fuel combustion.

Ammonia is a highly promising carbon-neutral fuel. The use of ammonia as a fuel for internal combustion engines can reduce fossil energy consumption and greenhouse gas emissions. However, the high ignition energy required for ammonia and the slow flame propagation rate result in low combustion efficiency when ammonia is used directly in internal combustion engines. The combination of ammonia with highly reactive fuels improves combustion quality and increases efficiency. However, the combustion of these combined fuels generates particulate matter, CO, hydrocarbon, and significant amounts of NOx. Therefore, pollutant emissions must be reduced through after-treatment technologies. In this paper, a series of combustion and post-treatment challenges faced by amino fuel combustion in internal combustion engines are extensively discussed and the combustion reaction mechanisms of different amino fuels are also analyzed. The paper then reviews five key technologies applicable to the reprocessing of amino fuels, including selective catalytic reduction, selective catalytic reduction filter technology, electrochemical methods for NOx removal, direct catalytic decomposition of N2O, and ammonia sliding catalysts. An in-depth discussion of the catalytic materials and reaction mechanisms involved in these technologies is also provided in this paper. Finally, the paper summarizes the main technical challenges that must be addressed for the future application of amino fuels in internal combustion engines. These discussions can serve as an essential reference for developing and applying critical technologies for combustion control and pollutant treatment of amino fuels.

Uniform and fully exposed Rh clusters on defect-rich CeO2 enable efficient catalytic N2O decomposition

Uniform and fully exposed Rh clusters on defect-rich CeO2 enable efficient catalytic N2O decomposition

Insights into the Roles of Different Iron Species on Zeolites for N2O Selective Catalytic Reduction by CO.

Iron zeolites are promising candidates for mitigating nitrous oxide (N2O), a potent greenhouse gas and contributor to stratospheric ozone destruction. However, the atomic-level mechanisms by which different iron species, including isolated sites, clusters, and particles, participate in N2O decomposition in the presence of CO still remain poorly understood, which hinders the application of the reaction in practical technology. Herein, through experiments and density functional theory (DFT) calculations, we identified that isolated iron sites were active for N2O activation to generate adsorbed O* species, which readily reacted with CO following the Eley-Rideal (E-R) mechanism. In contrast, Fe2O3 particles exhibited a different reaction pathway, directly reacting with CO to generate oxygen vacancies (Ov), which could efficiently dissociate N2O following the Mars-van Krevelen (MvK) mechanism. Moreover, the transformation of iron oxide clusters into undercoordinated FeOx species by CO was also revealed through various techniques, such as CO-temperature-programmed reduction (TPR), and ab initio molecular dynamics (AIMD) simulations. Our study provides deeper insights into the roles of different iron species in N2O-SCR by CO, and is anticipated to facilitate the understanding of multicomponent catalysis and the design of efficient iron-containing catalysts for practical applications.

Investigation of Nonmetal F‐doped Co3O4 as Catalyst for N2O Catalytic Decomposition

AbstractAn effective nonmetal F‐doped Co3O4 (F‐Co3O4) catalyst was prepared using co‐precipitation method, and its catalytic performance was investigated for N2O decomposition comparing with pure Co3O4 catalyst. The catalytic activity test indicates that F‐Co3O4 catalyst exhibits better activity with 100% N2O conversion at a reaction temperature of 380 °C, which is 80 °C lower than that of pure Co3O4. The characterization results show that F is successfully doped into the lattice of Co3O4 and replaces part of O sites, which enlarges the surface area, enhances the surface basicity, and leads to higher basic sites density on the surface of Co3O4. Moreover, F doping promotes the electron donation capacity of Co2+, weakening of Co─O bond and generation of more oxygen vacancies. The synergy of the above factors results in reduction of activation energy over F‐Co3O4 catalyst, thus F‐Co3O4 catalyst exhibits better catalytic performance than pure Co3O4 for N2O decomposition, even in the existence of O2 or H2O as impurity gas. Meanwhile, F‐Co3O4 catalyst also exhibits better stability than pure Co3O4. This work will provide practical reference for constructing efficient nonmetal‐doped Co3O4 catalysts for N2O decomposition.

Toxic gas molecules adsorbed on the original and metal-doped two-dimensional s-C3N4: A first-principles investigation

We theoretically investigate toxic gas molecules including CO, NO, NO2, SO2, and H2S adsorbed on the original s-C3N4 and Cu, V and Fe-doped s-C3N4. V- and Cu-doped s-C3N4 structures have the semiconductor-to-conductor transitions. All the gas molecules prefer to be adsorbed on the metal-doped s-C3N4 than the pristine one. In addition, it also reveals that both original and metal-doped s-C3N4 materials provide better adsorption performance than most reported CxNy ones. The ab initio molecular dynamics simulations illustrate that Cu-doped s-C3N4 obtain the capacity for the decomposition of H2S at 500 K. Similar decomposition of NO2, SO2 and H2S by Cu-doped s-C3N4, and NO2 and H2S by Fe-doped s-C3N4 could also be observed. The other molecules could desorb from metal-doped s-C3N4. In addition, the metal atoms selected for the metal-doped s-C3N4 are economically advantageous. Thus, the cheap-metal-doped s-C3N4 shows good gas adsorption and decomposition capacity, and these studies may provide insights for the applications of metal-doped s-C3N4.

Assessing the role of oxygen vacancies on N2O catalytic decomposition over CaMn1-xFexO3-δ perovskites

Catalytic decomposition of N2O using redox perovskites can efficiently mitigate industrial emissions of this molecule. Here, we have selected the CaMn1-xFexO3-δ (CMF) oxides as catalysts to explore the role of oxygen vacancies on N2O decomposition, because for these materials the thermodynamics of oxygen non-stoichiometry is known in detail Perovskites with two levels of Fe-doping, CMF73 (30 % at.) and CMF91 (10 % at.), were prepared and extensively characterized. Higher conversion is obtained over CMF73, which also presents good stability. In the presence of N2O, variation of temperature prompts this perovskite to quickly adjust the value of δ by reversible release/uptake of O2. In parallel, surface vacancies can participate in the breaking of the N-O bond, as a part of a regenerative catalytic cycle yielding N2 and O2. A simple kinetic model shows good correlation between the number of oxygen vacancies, estimated by δ, and the catalytic activity, explaining the better performance of CMF73.

Revealing Active Sites and Reaction Pathways in Direct Oxidation of Methane over Fe-Containing CHA Zeolites Affected by the Al Arrangement.

Fe-containing zeolites are effective catalysts in converting the greenhouse gases CH4 and N2O into valuable chemicals. However, the activities of Fe-containing zeolites in methane conversion and N2O decomposition are frequently conflated, and the activities of different Fe species are still controversial. Herein, Fe-containing aluminosilicate CHA zeolites with Fe species at different spatial distances affected by the arrangement of framework Al atoms were synthesized in a one-pot manner in the presence or absence of Na. The arrangement of framework Al atoms was identified by 27Al and 29Si MAS NMR spectra and thermogravimetry-differential thermal analysis (TG-DTA) curves. Ultraviolet (UV)-vis, X-ray absorption spectroscopy (XAS), and NO adsorption fourier transform infrared spectroscopy (FTIR) spectra were adopted to analyze Fe speciation. The higher proportion of Fe species in the 6 MR of Fe-CHA zeolites in the presence of Na was confirmed by the NO adsorption FTIR spectrum. The activities of proximal and distant Fe sites in reactions including direct oxidation of methane to methanol, methanol to hydrocarbon, and N2O decomposition were compared at different temperatures to provide the corresponding active sites and reaction pathways. The distant, isolated Fe and isolated proton were more active in the direct oxidation of methane to methanol and tandem conversion of methanol to hydrocarbon reactions than the proximal, isolated Fe and paired protons, respectively. Additionally, proximal, isolated Fe sites afforded higher activity in N2O decomposition. These findings guide the design of highly active catalysts in methane oxidation, methanol to hydrocarbon, and N2O decomposition reactions, addressing energy and environmental concerns.

The Behavior of Catalytic, Low-Temperature N2O Decomposition (LT-deN2O) in the Presence of Sulfur-Containing Compounds on Nitric Acid Plants

The Behavior of Catalytic, Low-Temperature N2O Decomposition (LT-deN2O) in the Presence of Sulfur-Containing Compounds on Nitric Acid Plants

NO Emission Characteristics of Pulverized Coal Combustion in O2/N2 and O2/H2O Atmospheres in a Drop-Tube Furnace.

Oxy-steam combustion is a new oxy-fuel combustion technology. This paper focuses on the NO emission characteristics during the combustion of SF (Shen Fu) coal in O2/N2 and O2/H2O mixtures. Experiments were performed in a drop-tube furnace. Combustion tests were carried out in O2/N2 and O2/H2O atmospheres for various O2 concentrations (21%, 30%, 40%, and 60%) at different temperatures (1173 K, 1273 K, and 1373 K). In addition, combustion experiments at different excess oxygen ratios (λ) were conducted in O2/N2 and O2/H2O atmospheres. The influences of the atmosphere, oxygen concentration, temperature, and excess oxygen ratio on NO emissions were analyzed. The results show that the NO concentrations of SF coal combustion in the 21% O2/79% H2O atmosphere were much lower than those in the 21% O2/79% N2 atmosphere at the three temperatures considered. This was because a large amount of NO was decomposed during the SF coal combustion in the O2/H2O atmospheres. The reasons for the decomposition of NO include the selective non-catalytic reaction (SNCR) mechanism and char's important role as a catalyst for the destruction of NO, either directly or by reacting with CO or H2. In oxy-steam combustion, the NO concentrations significantly increased with the increase in the oxygen concentration from 21 vol.% to 60 vol.% and the temperature from 1173 K to 1373 K. The excess oxygen ratio (λ) slightly impacted the NO emissions in the O2/H2O atmosphere.

Investigating combustion efficiency and NOx emission reduction in fluidized bed ammonia-coal co-firing

Ammonia, a carbon-free fuel, can significantly reduce CO2 emissions when co-fired with coal in power plants. Fluidized bed combustion, known for its excellent gas-solid mixing and low NOx emissions, is a promising method for ammonia-coal co-firing. However, challenges remain in optimizing ammonia injection and controlling nitrogen oxide emissions. This study investigates these aspects using a lab-scale fluidized bed reactor with flexible ammonia injection points. Key variables, such as ammonia co-firing ratios, injection location, temperature, and outlet oxygen concentration, are examined. The results show that with ammonia injection ratios up to 70 %, NO and N2O emissions slightly increase, while ammonia escape is maintained below 5 ppm. Air staging effectively controls NOx emissions, and higher temperatures promote N2O decomposition, but increase NOx levels. Ammonia injection does not raise unburned carbon content. Rate of production and sensitivity analyses highlight the role of OH radicals in ammonia conversion and identify the critical reactions affecting NO generation. This study highlights the feasibility of fluidized bed ammonia-coal co-firing technology.

Decomposition of N2O by Ruthenium Catalysts – RuO2 as Active Phase on Non‐Reducible Supports

AbstractRuthenium has been supported on specifically chosen non‐reducible supports (Al2O3, SiO2, Al2O3‐SiO2 mixed oxides, Mg/ZnAl2O4 spinel, and AlF3), and these catalysts have been tested in the decomposition of nitrous oxide, N2O, to identify the catalytically active phase of ruthenium. Pure, bulk ruthenium dioxide, RuO2, and isolated Ru surface complexes have been synthesized and investigated for comparison. The catalysts were characterized by X‐ray diffraction, H2 chemisorption, N2 physisorption, temperature‐programmed reduction, and desorption (TPR/TPD) and in situ infrared spectroscopy (IR). All aimed experiments strongly indicate that the decomposition of N2O occurs on ruthenium dioxide, RuO2, instead of metal particles. H2 pre‐reduction to Ru metal has inhibitory effects for all oxygen‐containing supports. The activity increases with the dispersion of ruthenium oxide. Bulk RuO2 showed the best catalytic performance.

Cement Clinker Modified by Photocatalyst—Selected Mechanical Properties and Photocatalytic Activity during NO and BTEX Decomposition

In this paper, a new way to obtain photoactive cements was presented. In this method amorphous TiO2 is added to a cooler during the cooling of the cement clinker (Górażdże company) during cement production. Amorphous TiO2 was taken from the installation for obtaining titanium dioxide using the sulphate method. During the study, amorphous TiO2 was added to the clinker at 300, 600, 700, and 800 °C. The properties of the obtained cement were tested during the bending and compressive strength. The initial and the end of setting time was also measured. The adhesion of the obtained materials to concrete block, ceramic brick, and plasterboard were also evaluated. The photocatalytic activity of the obtained materials was studied during NO and BTEX (benzene, toluene, ethylbenzene, p-, m-, o-xylenes decomposition) decomposition. Cement with 5 wt% TiO2 added to the clinker at 700 °C had the highest photocatalytic activity and the best mechanical properties.

On the Heterogeneity of Iron‐Oxo Species in Zeolites for the Oxidation of Methane to Methanol by Nitrous Oxide: A Theoretical Perspective

AbstractThe conversion of methane to methanol (MTM) represents a pivotal objective in the C1 chemical industry. Transition metals, such as iron, exchanged zeolites are one category of the most active catalysts for direct conversion of MTM. One important topic in understanding the mechanism of Fe‐zeolite catalyzed MTM is how the heterogeneity of catalytic (Fe) sites influences the system stability and reactivity. Employing DFT calculations and machine learning method, we herein studied the stability–reactivity relationship of a MTM catalytic cycle with N2O as the oxidant over Fe‐exchanged zeolites. The Fe heterogeneity was introduced by using CHA and FER zeolites and looking at a number of related Fe species (FeII, FeO, and FeOH). A strong correlation was observed between the stability of such Fe species, which is primarily determined by the formation energy of FeII, and such a stability trend remains consistent throughout the MTM catalytic cycle. The reactivity analysis then demonstrated that less stable Fe species may exhibit higher reactivities when situated in specific sites. Further machine learning analysis validated the significant relevance of activation barriers with reaction energies in the N2O decomposition step that is not sufficiently captured by the traditional one‐dimensional Brønsted–Evans–Polanyi (BEP) relationship.

Feasibility of using red mud as bed material for treating N2O in fluidized bed combustion

Red mud, a type of industrial waste, currently can’t be utilized effectively, and there are no efficient methods for controlling N2O emissions in circulating fluidized bed (CFB) boilers. Based on characteristics of N2O and the components of the red mud, the red mud was used in this study as bed materials of fluidized bed to treat N2O produced by coal combustion. The decomposition effect of red mud on N2O under various operating conditions during the coal combustion process was quantified in a bubbling fluidized bed, and the decomposition of N2O and NO after the flue gas passed through the bed material was investigated. In a variety of operational conditions, the presence of red mud has been observed to exert a pronounced inhibitory effect on the formation of N2O, while concurrently exhibiting the capacity to diminish the nitrogen conversion rate of N2O to varying degrees. Comparative analysis of N2O and NO emissions from char and coal revealed different levels of reduction, with the combination of CO and red mud being the most effective method. Red mud demonstrated superior N2O removal capabilities, while CO was more effective for NO removal. The issue of increasing NO can be resolved by balancing the iron-aluminum ratio of red mud, allowing the flue gas to pass through the red mud in the CFB’s low-temperature zone, and focusing on N2O removal in the furnace.