N2O Decomposition Research Articles

Ti3+ sites on mesoporous titania enable selective photocatalytic decomposition of NO to N2 and O2 under visible light

Ti3+ sites on mesoporous titania enable selective photocatalytic decomposition of NO to N2 and O2 under visible light

Efficient photocatalytic decomposition of NO and mechanism insight enabled by NaBH4-reduced N(ligancy-3)-vacancy-rich-graphitic carbon nitride

Vacancy defect engineering is an effective means to improve the performance of g-C3N4 photooxidation for NO removal. In this paper, flake graphite-phase g-C3N4 is prepared by thermal polycondensation. Then g–C3N4–x (x = 0, 0.5, 1.0, 1.5, and 2.0) containing various amounts of vacancies of nitrogen atoms with (3 coordination number) ligancy 3 (N(ligancy-3)) was prepared by NaBH4 reduction at room temperature. The introduction of N vacancies in g-C3N4 narrowed the forbidden gap, enhanced optical absorbance, optimized photo exciton separation and migration, and functioned as traps to mitigate the recombination of photogenerated electron-hole pairs. As a result, g–C3N4–x shows a superior NO removal performance, especially g–C3N4–1.5, which exhibits a high NO removal rate of 66.7 %, excellent resistance to the by-product NO2, and excellent stability. The free-radical seizure experiments and electron paramagnetic resonance (EPR) studies proved the superiority of superoxide radicals, electrons and holes as the prominent free radicals in the photocatalytic NO removal process. In situ diffuse infrared Fourier transform spectroscopy (DRIFTS) confirmed that the cis-dimer (NO)2 produced from NO adsorption on the surface of g–C3N4–1.5 is an important intermediate. Additionally, NO2− is observed as an intermediate and a primary product, and NO3− is identified as the key product of NO photocatalytic oxidation. DFT calculations showed that the N(ligancy-3) vacancy introduces impurity energy levels in g-C3N4 and shortens the electron migration path. The adsorption calculation of NO demonstrated that g–C3N4–N(ligancy-3) exhibits good adsorption and conversion of NO. This study provides a practical defect engineering for the g-C3N4 to remediate environmental pollution.

The influence of the synthesis route and microwave activation on the CuFe2O4 spinel mixed oxide catalysts activity in N2O decomposition

In this study a comprehensive analysis of the influence of synthesis route of CuFe2O4 spinel mixed oxides on their catalytic performance in the N2O decomposition was carried out. A co-precipitation technique allowed one to obtain the CuFe2O4 spinel with a higher specific surface area and pore volume compared to the synthesis with the application of organic additives. This resulted in better catalytic performance of the CuFe2O4 samples prepared by co-precipitation. The microwave activation step with the duration of 1 min during the co-precipitation synthesis led to the formation of the CuFe2O4 spinel with a higher content of oxygen vacancies per 1 m2 in comparison with the sample obtained without the microwave activation. This fact caused a significantly higher specific activity of the CuFe2O4 spinel synthesized with the application of 1 min microwave activation. The increase of the microwave treatment time led to the fast growth of the contents of the CuO and α-Fe2O3 phases, which are less active in the N2O decomposition, resulting in the activity drop.

First principles energetic span analysis of the activity of transition metal catalysts for N2O decomposition: The reversal of descriptor roles in the presence of NO

The utilization of NH3 combustion faces a significant hurdle in mitigating N2O emissions, a potent greenhouse gas. Current deNOx technologies struggle to effectively decompose N2O, especially under practical conditions due to inhibitory effects from exhaust stream components like O2, NOx, and H2O. This study employs first principles investigations to analyze N2O decomposition activity on precious (Ru, Rh), non-precious (Cu, Ni), and hybrid (Ru/Cu, Rh/Cu, Ru/Ni, Rh/Ni) catalysts. Many new Brønsted-Evans-Polanyi relations are established, enabling mechanistic analysis via the Energetic Span Model. The analyses reveal opportunities for enhancing catalytic activity by exploiting weak correlations between intermediates’ free energies. The model captures the inhibitory effects of surface-adsorbed NO on the N2O decomposition activity, aligning well with experimental observations and catalytic trends. The strong binding energy of adsorbed N2/N2O and O adatom is found to be a key descriptor of activity. It is found to aid the catalytic activity in the presence of NO but becomes limiting in its absence.

The Oscillatory Behaviour of Cu-ZSM-5 Catalysts for N2O Decomposition: Investigation of Cu Species by Complementary Techniques.

Copper-exchanged ZSM-5 (Cu-ZSM-5) is a promising catalyst thanks to the Cu redox pair. A particular feature of this material consists in the presence of spontaneous isothermal oscillations which take place during N2O decomposition reaction, depending on the operating conditions. In the present work, a set of five Cu-ZSM-5 catalysts was synthesised by three procedures and three different copper precursor concentrations: i) wet impregnation, ii) single ion exchange, and iii) double ion exchange. Catalytic tests revealed that the ion-exchanged samples exhibit a low catalytic activity and no oscillatory behaviour, except for the twice-exchanged sample which achieves an average N2O conversion of 26 % at 400 °C. Conversely, the impregnated samples reach higher levels of N2O conversion (66 % for Cu5ZSM5_WI and 72 % for Cu10ZSM5_WI) and demonstrate a similar oscillating pattern. Further investigations disclosed that the most active catalysts, characterised by the presence of oscillatory behaviour, have more abundant and easily reducible copper species (ICP, EDX and H2-TPR) which interact better with the zeolitic support (FT-IR). Catalytic tests under a long time on stream (TOS) suggest that either self-organised patterns or deterministic chaos can be achieved during the reaction, depending on the operating conditions, such as temperature and contact time.

Supported LaCoO3 perovskite-like oxides for N2O decomposition: The key role of the support nature and LaCoO3 content

In this work a detailed comparison of the N2O decomposition catalytic performance of LaCoO3 perovskite-like mixed oxides supported over different commercial materials was conducted. Zirconia-, silica- and γ-alumina-based supports were studied. Zirconia-based supports turned out to be the most applicable because of the formation of the pure LaCoO3 perovskite phase on their surface. Among these supports, ZrO2-La revealed to possess the best activity owing to the highest Co2+/Co3+ (0.82) and Oads./OL (0.67) ratios on its surface. The raw of activities was as follows: LaCoO3(20 %)/ZrO2-La > LaCoO3(20 %)/ZrO2 > LaCoO3(20 %)/ZrO2-W. When the LaCoO3 content in LaCoO3/ZrO2-La was 20 wt%, the maximum of activity was observed – 94.78 mmol(N2O)/[g(cat.)·h] at 450 °C. This fact was in accordance with the highest Co2+/Co3+ (0.82) and Oads./OL (0.67) ratios at the 20 wt% LaCoO3 content. Coordinatively unsaturated Co2+, forming Lewis acid-base pairs, were proposed to be the active sites of the zirconia-based LaCoO3 catalysts in the N2O decomposition.

Effects of Zn loading on ZnxCo1−xCo2O4 spinel catalysts for low-temperature catalytic decomposition of N2O in the presence of inhibitors

The recent advancement of NH3-based fuel demands the development of catalysts that can decompose N2O at low temperatures and are stable against various inhibitors. Zn-doped cobalt spinel (ZnxCo1−xCo2O4) catalysts have demonstrated superior activity for N2O decomposition at low temperatures. However, their optimization and deactivation mechanisms with respect to Zn loading when inhibitors are present require further investigation. Herein, we reviewed the effects of Zn loading on catalysts at low temperatures without or with the presence of inhibitors (3 vol% O2, 6 vol% H2O, 200 ppm NO). The results showed that adding an appropriate amount of Zn into Co3O4 spinel catalysts improves their N2O decomposition activity. The Zn-induced enhancement of the catalysts’ redox properties, and reducibility was the underlying mechanism behind the activity promotion. The presence of structural defects created through the addition of Zn enhanced the catalyst’s resistance to O2. The deactivation by H2O and NO upon the addition of Zn could be correlated with the reduced availability of surface Co species and Co2+ as adsorption-active sites and the stronger bond of Co with –NO, respectively. This study underscores the importance of controlling the Zn loading as a bulk redox promoter in ZnxCo1−xCo2O4 spinel catalysts for practical applications.

Effect of ammonia energy ratio and load on combustion and emissions of an ammonia/diesel dual-fuel engine

Ammonia is receiving increasing attention as a zero-carbon fuel. However, it is difficult to use alone because of its high auto-ignition temperature. Therefore, in this paper, the effects of four ammonia energy ratios (15 %, 30 %, 45 %, and 60 %) on the combustion and emission characteristics of the engine at different loads were studied by using the ammonia/diesel dual-fuel strategy. The results indicated that the presence of ammonia lowered the combustion temperature at all loads, thereby lowering the cylinder temperature and cylinder pressure. In addition, the HRR first increased and then decreased as the ignition delay increased with the increase in ammonia energy ratio. In terms of emissions, at 100 % load, the CO2 and NO of the D40A60 were 65.5 % and 88.14 % lower than that of the D100. The decrease in CO2 was due to more carbon-based fuels being replaced by ammonia. The decrease in NO was due to the decomposition of NO by the thermal deNOx reaction resulting from the lower combustion temperature. The emissions of N2O produced by partial ammonia oxidation offset the greenhouse gas emission reduction effect caused by the reduction of carbon dioxide emissions. Further optimization of the engine combustion strategy is still needed in the future.

Excellent catalytic activity for NO decomposition on Rhn supported on grain-boundary terminations of the MgO (0 0 1) surface

In the present study, we first propose the grain-boundary termination of the MgO (001) surface (referred as GB@MgO(001)) as the substrate to support a series of Rhn clusters to trap and dissociate NO. Using van der Waals density functional theory calculations, we have studied the interaction between the Rhn (n = 1 ∼ 8) cluster and the MgOΣ5(210)GB@MgO(001) and the properties of the adsorption and dissociation of NO on Rhn/GB@MgO(001) systems. The Rhn clusters can tightly bond to the GB@MgO(001), with interfacial interactions comparable to those at the Rhn/MgO-nanotube interface. Stable quasi-two-dimensional Rhn clusters provide more active sites to NO. Moreover, NO dissociation is activated, with all the complete reaction paths occur below the reference state, indicating the possibility of the NO decomposition. An extremely small energy barrier of 0.037 eV was obtained for NO dissociating on the square-Rh4/GB@MgO(001) system. Molecular dynamic (MD) calculations reveal that NO can be completely decomposed at 527 K without obvious structure distortions of the complex. The adsorption of NO yields a change in the total magnetic moment of the Rhn/GB@MgO(001) system, but it has a minimal impact on the adsorption energy of NO. Our results also show that the optimal Rhn clusters that are good at trapping and dissociating NO are not the most stable structures, but rather clusters of relatively low dimension that are bound to the substrate with a moderate strength. As a result, the modification and tuning of the substrate structure can effectively enrich the structure of Rh cluster catalyst and improve its physical properties so that it can potentially play a greater role in other redox reactions, which motivates us to continue designing various types of GB@MgO(001) for different purposes.

New Method for Photoactive Cement Preparation-Selected Mechanical Properties and Photocatalytic Activity of New Materials.

In this study, a new method of obtaining photoactive cements is presented. The goal was to obtain photoactive cements using a method that could reduce the production costs. In the study, an intermediate product from the production of titanium dioxide using the sulfate method, taken from the installation before the calcination process, was used to obtain photoactive cements. Laboratory conditions corresponding to introducing this amorphous TiO2 into cement clinker during its cooling were simulated. The study shows that the temperature from 300 to 800 °C and the time of amorphous TiO2 contact with the cement clinker within 30 min is sufficient to obtain a photoactive cement. The highest photocatalytic activity was obtained for the material with 5 wt.% TiO2 content, and the method used did not cause a significant decrease in the bending and compressive strength of the new photoactive cements. The obtained materials were characterized by determining the crystal size of the TiO2, the sulfur content and the photocatalytic activity during NO decomposition under UV radiation. The bending and compressive strength were measured. The influence of the addition of photocatalysts on the beginning and end of the setting time was also investigated.

High-efficient N2O decomposition over dual-phase hydrogen/oxygen-transporting membrane reactors

Nitrous oxide (N2O) emissions sourced from agricultural and industrial activities have gained much attention because of their contribution to the global greenhouse effect and ozone layer depletion. Significant efforts have been devoted to developing the cost-effective and highly efficient technologies for N2O removal. The direct N2O decomposition is limited by the thermodynamic equilibrium at high temperatures. Recently, catalytic reduction of N2O with carbon-free hydrogen derived from in situ ammonia decomposition is considered as an ideal approach. Herein, thermal decomposition of N2O is investigated by employing a BaCe0.85Fe0.15O3-δ-BaCe0.15Fe0.85O3-δ (BCF8515-BCF1585) hydrogen-transporting membrane or a Ce0.85Sm0.15O1.925-Sm0.6Sr0.4FeO3-δ (SDC-SSF) oxygen-transporting membrane respectively. It is noted that the membrane catalysis of N2O decomposition by reacting with permeated hydrogen or via in-situ oxygen removal displayed significant advantages over the direct thermal decomposition of N2O under a fixed bed condition. Moreover, the N2O conversion as well as hydrogen/oxygen permeability of such membranes were greatly improved by the introduction of porous Ni–CeO2 or SDC-NCO layers due to the increased catalytic activities and hydrogen/oxygen surface exchange kinetics.

NO Dissociation on Platinum and Platinum-Rhodium Alloy: A Theoretical Investigation

In this computational study, the preferential adsorption and co-adsorption sites of various chemical species (N, O, and NO) on the Pt (111) and Rh3Pt (111) surfaces were identified. The preferential adsorption site for NO and co-adsorption sites for N and O on the Pt (111) surface are the hollow (fcc) sites; and these on the Rh3Pt (111) surface are the hollow (fcc1) site and hollow N(hcp2)-O(fcc1) sites, respectively. The activation energies of the NO dissociation reaction on the Pt (111) and Rh3Pt (111) catalytic surfaces are 2.35 and 2.02 eV, respectively. The lower activation energy of the NO decomposition on the Rh3Pt (111) surface is explained by the stronger back-donation from the 4d orbital of the Rh atoms to the 2π* anti-bonding orbital of the NO molecule. The activation energies of the N and O recombination reaction on the Pt (111) and Rh3Pt (111) catalytic surfaces are 1.51 and 2.30 eV, respectively. The study indicates that the Rh3Pt (111) surface not only facilitates the NO decomposition but also better prevents N and O from recombination. Copyright © 2024 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Application of Mesoporous/Hierarchical Zeolites as Catalysts for the Conversion of Nitrogen Pollutants: A Review

Mesoporous/hierarchical zeolites (HZs) are a relatively new group of materials, and interest in their application in catalysis is continuously growing. This paper presents recent achievements in the application of mesoporous zeolites in catalytic reactions of nitrogen pollutant conversion. The analysis presented includes processes such as selective catalytic reduction of NOx with ammonia (NH3-SCR, DeNOx), selective catalytic oxidation of ammonia (NH3-SCO, AMOx), and catalytic decomposition of N2O. Different zeolite topologies and methods of their modification focused on mesoporosity generation (e.g., desilication, dealumination, steaming, self-assembly techniques, and application of hard and soft templates) are reviewed and compared with respect to catalytic processes. Special attention is paid to the role of porous structure and acidity, as well as the form of deposited transition metals, in the catalytic activation of modified zeolites in the elimination of nitrogen pollutants from flue gases.

Cost modeling of photocatalytic decomposition of atmospheric methane and nitrous oxide

Abstract The photocatalytic decomposition of atmospheric methane (CH4) and nitrous oxide (N2O) could be valuable tools for mitigating climate change; however, to date, few photocatalyst deployment strategies have had their costs modeled. Here, we construct basic cost models of three photocatalytic CH4 and N2O decomposition systems: 1) a ground-based solar system with natural airflow over photocatalyst-painted rooftops, 2) a ground-based LED-lit system with fan-driven airflow, and 3) an aerosol-based solar system on solid particles dispersed in the atmosphere. Each model takes as inputs the photocatalyst’s apparent quantum yield (AQY; a measure of how efficiently photons drive a desired chemical reaction) and the local CH4 or N2O concentration. Each model calculates an overall rate of greenhouse gas drawdown and returns a levelized cost of greenhouse gas removal per equivalent ton of carbon dioxide (tCO2e). Based on prior studies of atmospheric carbon dioxide removal, we adopt $100/tCO2e as a target cost.

We estimate that painting rooftops with photocatalysts might meet the target cost for decomposition of >10ppm CH4 with catalyst AQYs >4%. If painting and cleaning costs were reduced by a factor of ~3 from our scenario, removal of ambient CH4 could meet the cost target with AQYs >1% and removal of ambient N2O could do so with AQYs >0.1%. 
Fan-driven systems with LED illumination appear to be very challenging, achieving removal costs <$100/tCO2e only for AQYs of >10% for CH4 and >1% for N2O. Dispersing photocatalytic aerosols in the troposphere could be cost-effective with AQYs of >0.4% for ambient CH4 or >0.04% for ambient N2O. However, the mass of aerosols required is large and their side effects and social acceptability are uncertain. We note that, for any system, AQYs on the order of 1% will likely be extremely challenging to achieve with such dilute reagents.

High-Efficiency Electrocatalytic Reduction of N2O with Single-Atom Cu Supported on Nitrogen-Doped Carbon.

Nitrous oxide (N2O) is a potent greenhouse gas with a high global warming potential, emphasizing the critical need to develop efficient elimination methods. Electrocatalytic N2O reduction reaction (N2ORR) stands out as a promising approach, offering room temperature conversion of N2O to N2 without the production of NOx byproducts. In this study, we present the synthesis of a copper-based single-atom catalyst featuring atomic Cu on nitrogen-doped carbon black (Cu1-NCB). Attributed to the highly dispersed single-atom Cu sites and the effective suppression of the hydrogen evolution reaction, Cu1-NCB demonstrated an optimal N2 faradaic efficiency (82.1%) and yield rate (3.53 mmol h-1 mgmetal-1) at -0.2 and -0.5 V vs RHE, respectively, outperforming previously reported N2ORR electrocatalysts. Further, a gas diffusion electrode cell was employed to improve mass transfer and achieved a 28.6% conversion rate of 30% N2O with only a 14 s residence time, demonstrating the potential for practical application. Density functional theory calculations identified Cu-N4 as the crucial active site for N2ORR, highlighting the significance of the unsaturated coordination and metal-support electronic structure. O-terminal adsorption of N2O was favored, and the dissociative adsorption (*ON2 → *O + N2) was the rate-determining step. These findings reveal the broad prospects of N2O decomposition via electrocatalysis.

Tuning the A‐site Element in LaCo0.8Fe0.2O3 Perovskite‐based Catalyst for High Temperature N2O Decomposition in Nitric Acid Plant

AbstractThe effect of La‐deficiency and Ce/Sr‐substitution in the benchmark LaCo0.8Fe0.2O3 has been investigated for the decomposition of N2O between 500 and 900 °C. Real inlet gas composition and space velocity reveal that La‐deficiency and Ce/Sr‐substitution can improve the thermal stability of catalyst, while La1‐xSrxCo0.8Fe0.2O3 with x≥0.1 was highlighted as a promising formula due to the strongest resistance to deactivation and suppressed undesired NOx decomposition at high space velocity. This phenomenon is mainly ascribed to the incorporation of Sr2+ into the perovskite lattice during the reaction consequently stabilizing the Co3+ species and creating the oxygen vacancies in La1‐xSrxCoO3‐δ. On the contrary, the loss of activity on Ce‐substituted LaCo0.8Fe0.2O3 has been preferentially related to the cobalt exsolution to extra framework of perovskite making the catalytic cycle with Co3+ unfavorable. All these bulk and surface changes are accompanied with opposite evolution of apparent activation energy and pre‐exponential factor which can be discussed based on a redox mechanism.

High-temperature resistant BaO-Y2O3 catalysts with different morphologies for NO decomposition and mechanism study

The high-temperature reaction is a common phenomenon in combustion society, and its catalytic response remain a tremendous challenge hampered by the activity and resistance of the catalyst to high temperatures exceeding 1000 ℃. Three distinct forms of BaO-Y2O3 catalysts—nanosphere, nanorod, and rod—were created using a hydrothermal method and high-temperature annealing to enable direct decomposition of NO. To gather reaction-relevant structural and property information for BaO-Y2O3, we combined reactor activity measurements, chemisorption and DFT studies to elucidate NO high-temperature decomposition process and pinpoint the critical role of oxygen vacancy. We have systematically clarified the increasing favorability of NO decomposition on the nano-catalysts (nanospheres and nanorods) at high temperatures is through stable lattice structure, large specific surface areas, high porosity, and active Ba–O–Y bond. Due to the attraction of electrons gathering in vacancies to NO molecules, oxygen vacancies created in situ at high temperatures, as validated by O2-TPD and density functional theory (DFT) calculations, are advantageous for NO adsorption and decomposition. Moreover, N2 formation pathway over Ba-Y2O3(111) structure is revealed by DFT calculations that NO molecules are apt to be caught by active sites, the region of Ba–O–Y, resulting in the production of N2O2 intermediate and its subsequent bond breaking to N2O as well as N2. In situ DRIFTS experiment further confirms the reaction mechanism via the detected adsorbed species, and clarify the significance of NO2− to O2 formation. In a nutshell, the synthetic combustion catalysts are effective in high-temperature environments that contribute to de-NOx combustion, and the insights into the adsorption configurations of reactant and intermediates unlock fundamental understanding for emissions gas chemistry.

Facile Synthesis of N-doped Co3O4 Catalyst for Catalytic Decomposition of N2O under Simulated Real Tail Gases

Facile Synthesis of N-doped Co3O4 Catalyst for Catalytic Decomposition of N2O under Simulated Real Tail Gases

Conceptual design of a fixed bed N2O decomposition reactor with a heat pipe heat exchanger

Abstract This paper introduces a novel process for decomposing N2O through interstage cooling utilizing a heat pipe heat exchanger. The reactor design involves segmenting the fixed bed reactor into multiple layers and integrating heat pipe heat exchangers between these layers to efficiently dissipate the high heat generated by the upper fixed bed reactor. This innovative approach facilitates the direct decomposition of N2O feedgas with high concentrations, obviating the need for gas dilution. The study conducted in this paper employed Fluent and ASPEN PLUS to investigate N2O decomposition with interstage cooling using heat pipe heat exchangers, as well as decomposition after dilution. A comparison between the two methods was made based on catalyst dosage, temperature uniformity, and reactor energy consumption. The results demonstrate that the proposed method for N2O decomposition via interstage cooling with a heat pipe heat exchanger is a viable option, offering the desired temperature control and enhanced efficiency. Furthermore, this reactor design effectively reduces both catalyst usage and energy consumption, providing substantial advantages over traditional approaches.

A DFT study on Cu-ZSM-5 as a catalyst for NO decomposition: Possible activity of a Cu(I) pair located at the T3 tetrahedral sites

The decomposition of NO catalysed by Cu+ pairs coordinated at the Al-substituted T3 sites of the 10-membered rings of Cu-ZSM-5 was studied by means of DFT/ONIOM calculations. Three mechanisms for NO decomposition were defined on the active site, all based on the formation and further decomposition of an hyponitrite anion, which gives the N2O molecule and a [Cu‒O‒Cu]2+ bridge, where both copper ions are oxidized. N2O can react with the oxidized active site according to two different spin-allowed mechanisms which give immediately the products, N2 + O2. Otherwise, N2O reacts with a new reduced site according to a spin-forbidden mechanism which gives N2 and a second [Cu‒O‒Cu]2+ bridge. When the latter mechanism occurs, reduced sites are restored by further reaction of [Cu‒O‒Cu]2+ with NO and desorption of NO2, which is finally decomposed on a second [Cu‒O‒Cu]2+ site, giving O2 + NO. Turnover frequencies (TOFs) calculated by means of the Energetic Span model showed that one of the spin-allowed mechanisms should be relatively fast, whereas the spin-forbidden one is expected to be extremely slow. Computational results were discussed with reference to experimental data available in the literature.