Direct Decomposition Of NO Research Articles

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.

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.

Distinct structure-activity relationship and reaction mechanism over BaCoO3/CeO2 catalysts for NO direct decomposition

The dependency on morphology is crucial for achieving highly efficient direct decomposition of NO. Herein, a BaCoO3/CeO2 catalyst is synthesized using CeO2 small particles (p), spheres (s) and rods (r) as supports. The NO conversion to N2 (NTN2) at 800 °C follows the order BaCoO3/CeO2-r (78.8 %) > BaCoO3/CeO2-s (75.9 %) > BaCoO3/CeO2-p (56.9 %) > BaCoO3 (8.6 %) at a space velocity 1 g s/cm3. BaCoO3/CeO2-r exhibts high tolerance to O2 and stability with conversion decreasing from 78.8 % to 74.6 %, 60.0 % and 50.0 % at 800 °C with 1, 5 and 10 vol% O2, respectively. The high redox activity, higher active oxygen mobility and NO adsorption capability ensures its superior performance, while the high surface area (31.29 m2/g) and uniform distribution of active sites on the surface further promote the activity. The mechanism of NO direct decomposition is elucidated by in situ Diffuse reflectance infrared Fourier transform spectroscopy, 18O2 isotopic transient exchange experiments and density functional theory (DFT) calculation.

Support effect and reaction pathway for NO direct decomposition over CuMn/A (A=ZSM-5, Beta, SSZ-13) catalysts

The CuMn/ZSM-5 (CM/Z), CuMn/Beta (CM/B), and CuMn/SSZ-13 (CM/S) catalyst samples were prepared via an excess impregnation method to investigate the metal-support effect. The results show that the activity at 550 °C for NO direct decomposition follows the order of CM/Z (53.4%) > CM/B (49.2%) > CM/S (7.9%). The good activity and stability of CM/Z are attributed to a strong support effect including forming more active copper sites of the (Cu2+-O2--Cu2+)2+ and (Cu+-□-Cu+)2+ dimers, which have higher redox activity, capacity of oxygen mobility, and NO sorption capability. The competitive adsorption between NO and O2 on the oxygen vacancy of dimers over CM/Z results in the activity decrease from 53.4% to 40.3% at 550 °C after adding 1 vol% O2. The reaction mechanism over CM/Z was discussed based on the in situ DRIFT and isotopic (18O2) experiments. Two NO adsorbs firstly on (Cu+-□-Cu+)2+ to form N2O, and N2O is activated to produce N2, followed by the NO adsorption on (Cu2+-O2--Cu2+)2+ to form nitrite and nitrate species and decomposition to NO and O2.

Efficient Direct Decomposition of NO over La0.8A0.2NiO3 (A=K, Ba, Y) Catalysts under Microwave Irradiation

Efficient Direct Decomposition of NO over La0.8A0.2NiO3 (A=K, Ba, Y) Catalysts under Microwave Irradiation

Density Functional Theory Study of Mechanism of Reduction of N2O by CO over Fe-ZSM-5 Zeolites

Nitrous oxide (N2O) is an industrial waste gas (e.g., from the production of adipic acid), which damages the ozone layer and causes the greenhouse effect. Density functional theory calculations were employed to investigate the mechanism of direct catalytic decomposition of N2O and selective catalytic reduction (SCR) of N2O by CO over Fe-ZSM-5 zeolites. Two stable Fe-active sites with six-membered ring structures on Fe-ZSM-5 were considered. The calculations indicate that the decomposition of N2O is affected by the coordination environment around Fe and can occur through two reaction pathways. However, there is invariably a more considerable energy hurdle for the initiation of the second stage of N2O decomposition. When CO participated in the reaction, it showed good reactivity and stability, the reaction energy barriers of the rate-limiting step were reduced by roughly 20.57 kcal/mol compared to the direct catalytic decomposition of N2O. CO exhibited a superior electron-donating ability and orbital hybridization performance during the reaction, which enhanced the cyclicity of the N2O reduction catalytic process. Our calculations confirmed the significant role of CO in N2O reduction over Fe-ZSM-5 observed in previous studies. This study provides a valuable theoretical reference for exploring CO-SCR methods for N2O reduction over Fe-based zeolite catalysts.

Low-temperature direct decomposition of NO over Rh/NC-MnFe catalyst: activity, stability and mechanism

As the ideal NO removal technology, the biggest challenge associated with the direct catalytic decomposition of NO is the development of highly active deNOx catalysts at low temperatures.

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.

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.

In-situ polymerization intercalation of montmorillonite to achieve Co3O4 barrier dispersion for direct catalytic decomposition of N2O

Herein, the Co-MMT (Co3O4-montmorillonite) catalysts were prepared by coordination-deposition (Co(0.015)-MMT-2(CD)) and deposition-precipitation method (Co(0.015)-MMT-2 (DP)) for the N2O direct decomposition, respectively. The structure, texture, and surface properties of the catalysts are characterized by XRD, TEM, FT-IR, Raman, XPS, and so on. The results show that compared with Co(0.015)-MMT-2(DP), Co(0.015)-MMT-2(CD) achieves barrier dispersion of active phase (Co3O4) by using the layer structure of montmorillonite and has a smaller Co3O4 crystal size, richer oxygen vacancy and higher content of Co2+Oh. In addition, the results of DFT calculation and kinetic calculation indicate that Co2+Oh possesses higher reaction activity than Co2+Td and Co3+Oh, and the TOF value of Co(0.015)-MMT-2(CD) at 400 ℃ is 3 times higher than that of Co(0.015)-MMT-2(DP). Therefore, the Co(0.015)-MMT-2(CD) catalyst shows excellent catalytic activity and tolerance to impurity gases (H2O, NO, and O2), and it can maintain 100% conversion at least 50 h for the direct catalytic decomposition of N2O.

Advances in Catalytic Decomposition of N2O by Noble Metal Catalysts

Nitrous oxide (N2O) is an environmental pollutant that has a significant greenhouse effect and contributes to the depletion of the ozone layer. To address the issues caused by N2O, direct catalytic decomposition of N2O to N2 and O2 has been demonstrated as one of the most efficient methods for its removal. Various metals, particularly noble metals, including Rh, Ru, Pd, Pt, Au, and Ir, have been widely used and investigated as catalysts to facilitate this transformation. Therefore, this review aims to provide an overview of the advances in noble metal-based catalysts studied in recent years. The comprehensive discussion includes the influence of multiple factors, such as catalyst supports, preparation methods, additives, and impurity gases (such as O2, H2O, SO2, NO, and CO2) on the performance of versatile catalysts. Furthermore, this review offers insights into the future trends of catalyst systems for the direct catalytic decomposition of N2O.

Catalytic decomposition of NO using molten gallium: an experimental and computational study

Molten gallium (Ga) catalyzes the direct decomposition of NO. In a bubble column reactor, NO decomposition was conducted by injecting NO-containing bubbles into molten Ga at elevated temperatures (> 400 °C), and > 90% conversion was achieved in only ∼ 0.2 s of residence time at 550 °C. Computational analysis showed that despite the weak binding energy of NO to Ga surface (34.4 kJ/mol), thermodynamically favored NO* dissociation on Ga (−138.3 kJ/mol) facilitated decomposition. Although Ga surfaces can be poisoned by O* generated by the dissociation of NO*, introducing reduction gas promoted OH* formation (−51.1 kJ/mol) on the surface and subsequent H2O desorption, and consequently reactivated the Ga surface. NO decomposition and catalyst regeneration using reducing gas was repeated over 15 cycles in a single droplet reactor, and NO conversion was stably maintained. Experimental and computational results support the potential use of molten Ga as a catalyst for the direct decomposition of NO.

How hydroxyapatite governs surface Cu(II) and Fe(III) structuring: Effects in the N2O decomposition under highly oxidant atmosphere

In this work, we present copper- or iron-loaded hydroxyapatite samples as active catalysts in the direct N2O decomposition reaction. Hydroxyapatite, functionalized with increasing amount of Cu(II) or Fe(III) species (from 3 to 9 wt%), were characterized by XRPD, DR UV-Vis, XPS, CO-adsorption followed by FT-IR, TEM-EDS, and tested in the N2O decomposition. Stability tests (550 °C, 72 h), reusability, resistance to sulfur (50 ppm) and to alkali (ca. 1 wt% of K or Ba) completed the study of the catalyst performances. Copper catalysts showed superior performances than iron counterparts. The structural evolution of the metal species with loading plays a critical role in the catalytic behavior. In the case of Fe-catalysts, a gradual Fe-coverage of HAP surface resulted in an increasing trend in the activity. Conversely, for Cu-catalysts high activity and selectivity were associated with a moderate structuration of Cu(II) in the form of nanoparticles with size of around 1.6 nm.

Non-thermal Plasma Synergizes High-Alkalinity Hydroxyapatite Supported RhFe Bimetallic Catalyst for Direct Catalytic Decomposition of N2O at Low Temperature

Non-thermal Plasma Synergizes High-Alkalinity Hydroxyapatite Supported RhFe Bimetallic Catalyst for Direct Catalytic Decomposition of N2O at Low Temperature

Effect of Zinc on the Structure and Activity of the Cobalt Oxide Catalysts for NO Decomposition

Co4−iZniMnAlOx mixed oxides (i = 0, 0.5 and 1) were prepared by coprecipitation, subsequently modified with potassium (2 or 4 wt.% K), and investigated for direct catalytic NO decomposition, one of the most attractive and challenging NOx abatement processes. The catalysts were characterised by atomic absorption spectroscopy, powder X-ray diffraction, Raman and infrared spectroscopy, temperature-programmed reduction by hydrogen, the temperature-programmed desorption of CO2 and NO, X-ray photoelectron spectroscopy, scanning electron microscopy, the work function, and N2 physisorption. The partial substitution of cobalt increased the specific surface area, decreased the pore sizes, influenced the surface composition, and obtained acid-base properties as a result of the higher availability of medium and strong basic sites. No visible changes in the morphology, crystallite size, and work function were observed upon the cobalt substitution. The conversion of NO increased after the Co substitution, however, the increase in the amount of zinc did not affect the catalytic activity, whereas a higher amount of potassium caused a decrease in the NO conversion. The results obtained, which were predominantly the acid-base characteristics of the catalyst, are in direct correlation with the proposed NO decomposition reaction mechanisms with NOx− as the main reaction intermediates.

Enhanced SO2 Resistance of Cs-Modified Fe-HZSM-5 for NO Decomposition

Direct decomposition of NO into N2 and O2 is an ideal technology for NOx removal. Catalyst deactivation by sulfur poisoning is the major obstacle for practical application. This paper focuses on strengthening the SO2 resistance of metal-exchanged HZSM-5 catalysts, by investigating the metals, promoters, preparation methods, metal-to-promoter molar ratios, Si/Al ratios and metal loadings. The results show that in the presence of SO2 (500 ppm), Fe is the best compared with Co, Ni and Cu. Cs, Ba and K modification enhanced the low-temperature activity of the Fe-HZSM-5 catalyst for NO decomposition, which can be further improved by increasing the exchanged-solution concentration and Fe/Cs molar ratio or decreasing the Si/Al molar ratio. Interestingly, Cs-doped Fe-HZSM-5 exhibited a high NO conversion and low NO2 selectivity but a high SO2 conversion within 10 h of continuous operation. This indicates that Cs-Fe-HZSM-5 has a relatively high SO2 resistance. Combining the characterization results, including N2 physisorption, XRD, ICP, XRF, UV–Vis, XPS, NO/SO2-TPD, H2-TPR and HAADF-STEM, SO42− was found to be the major sulfur species deposited on the catalyst’s surface. Cs doping inhibited the SO2 adsorption on Fe-HZSM-5, enhanced the Fe dispersion and increased the isolated Fe and Fe-O-Fe species. These findings could be the primary reasons for the high activity and SO2 resistance of Cs-Fe-HZSM-5.

Al-Decorated C2N Monolayer as a Potential Catalyst for NO Reduction with CO Molecules: A DFT Investigation.

Developing efficient and economical catalysts for NO reduction is of great interest. Herein, the catalytic reduction of NO molecules on an Al-decorated C2N monolayer (Al-C2N) is systematically investigated using density functional theory (DFT) calculations. Our results reveal that the Al-C2N catalyst is highly selective for NO, more so than CO, according to the values of the adsorption energy and charge transfer. The NO reduction reaction more preferably undergoes the (NO)2 dimer reduction process instead of the NO direct decomposition process. For the (NO)2 dimer reduction process, two NO molecules initially co-adsorb to form (NO)2 dimers, followed by decomposition into N2O and Oads species. On this basis, five kinds of (NO)2 dimer structures that initiate four reaction paths are explored on the Al-C2N surface. Particularly, the cis-(NO)2 dimer structures (Dcis-N and Dcis-O) are crucial intermediates for NO reduction, where the max energy barrier along the energetically most favorable pathway (path II) is as low as 3.6 kcal/mol. The remaining Oads species on Al-C2N are then easily reduced with CO molecules, being beneficial for a new catalytic cycle. These results, combined with its low-cost nature, render Al-C2N a promising catalyst for NO reduction under mild conditions.

Direct decomposition of NO over 8MR in high silica Cu-LTA zeolite: A DFT study on reaction mechanisms, thermodynamics and kinetics

NO is a principal air pollutant that has received increasing attention due to its harmful impact on the environment and human health. Direct catalytic decomposition of NO to N2 is a process that carries promising potential with further development of metal-exchanged zeolitic catalysts, while the challenge lies with the thermal durability of the catalysts. Several reports have cited Cu-loaded high silica to aluminium ratio (SAR) Linde Type A (LTA) zeolites to be effective deNOx catalysts with their high catalytic activity and hydrothermal stability, but the detailed mechanisms by which it acts are still poorly understood. In this study, both the Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) processes were discussed to elucidate a feasible reaction pathway that allows NO to be directly converted to N2O over the loaded-Cu in the eight-member ring (8MR) of the high silica LTA. The results have indicated that the L-H process is the most favourable pathway for the given temperature window (298.15–900 K). In addition, as the oxidation intermediate Cu-O hindered the desired NO conversion, multiple gaseous components (NO, CO, N2) that frequently existed in the catalytic process were considered for residual O (Ores) removal. NO and CO were both determined to be more favourable than N2 as reductants for the Ores removal, in consideration of their kinetic and thermodynamic characters. As a result, the high silica Cu-LTA showed catalytic feasibility in direct NO conversion from mechanistic insights.

Highly efficient NO direct decomposition over BaMnO3-CeO2 composite catalysts

Developing high-performance catalyst is of paramount importance for NO direct decomposition. Here, composite catalysts BaMnO3-CeO2 were designed and prepared by the one-pot method, which show high catalytic activity, oxygen resistance and durability. The NO conversion to N2 of 85.9% at 800 °C is achieved over 5%BaMnO3-CeO2. It exhibits 66.5% activity in the presence of 10 vol% O2 and runs stable for more than 200 h in 5 vol% O2 at 800 °C. The high performance is originated from the strong interaction between BaMnO3 and CeO2 components, where CeO2 can effectively inhibit the sintering of BaMnO3 particles, enhance the redox activity, mobility of lattice oxygen and NO sorption. The proposed catalytic mechanism based on diffuse reflectance infrared Fourier transform spectroscopy and kinetic study reveals that the formation of N2O* intermediate species is the rate determining step. BaMnO3-CeO2 composite can be a promising catalyst candidate for NO direct decomposition.

Carbonaceous materials are not suitable catalysts for direct NO decomposition in exhaust aftertreatment

New approaches for direct NO decomposition catalysis are urgently needed, but using carbonaceous supports appears not to be the way to go.