Catalytic Decomposition Of N2O Research Articles

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.

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

High-temperature treatment promotes N2O decomposition over Fe-impregnated Al-rich SSZ-13 zeolites

Fe/SSZ-13 catalysts were prepared via the impregnation method and calcined at different temperatures. The catalytic activity of Fe/SSZ-13 catalysts in the N2O catalytic decomposition reaction was greatly influenced by the calcination temperature. As the calcination temperature rose to 800 °C, the catalytic efficiency of N2O decomposition performance gradually improved. Nevertheless, if the temperature of calcination exceeded 800 °C, the efficiency diminished as a result of the disintegration of the molecular sieve framework. Various characterization methods were used to investigate the impact of calcination temperature on iron species. The results showed that the high-temperature treatment could promote the dispersion and reduction of Fe2O3 particles on the catalyst surface, which led to the generation of more active species (such as Fe3O4 and FeO) and provided more oxygen vacancies which favored the N-O breakage, thus improving the N2O decomposition activity.

Enhancement of N2O decomposition performance by co-doping of Ni and Y to Co3O4 catalyst

Co3O4, Y2O3-Co3O4 and NiO-Y2O3-Co3O4 samples were prepared by the simple co-precipitation method, and their N2O catalytic decomposition performance was evaluated. Experimental results disclose that the order of catalytic activity among the three catalysts is NiO-Y2O3-Co3O4 > Y2O3-Co3O4 >> Co3O4. N2O conversion over NiO-Y2O3-Co3O4 catalyst reached 100 % at 360 °C, which was 20 °C and 60 °C lower than those over Y2O3-Co3O4 and Co3O4, respectively. In addition, NiO-Y2O3-Co3O4 catalyst shows better water resistance compared with Co3O4 and Y2O3-Co3O4. Systems-based characterization techniques, it is confirm that Y and Ni were successfully doped into Co3O4, where Y was on the surface and Ni was mainly in the bulk phase. Due to the co-doping of Y and Ni, NiO-Y2O3-Co3O4 catalyst has smaller average particle size and reinforced surface alkalinity. Furthermore, the surface modification of Y enhances the electron-donating capacity of Co2+ and oxygen desorption ability, while bulk phase doping of Ni facilitates the reduction of Co3+ to Co2+ and weakens Co-O bond in Co3O4, which endow NiO-Y2O3-Co3O4 sample with lower Ea for N2O decomposition. Therefore, NiO-Y2O3-Co3O4 catalyst exhibits the best N2O catalytic decomposition performance.

Enhanced N2O decomposition on Rh/ZrO2 catalysts through the promotional effect of palladium

Supported rhodium oxide (RhOx) catalysts have emerged as highly promising for effectively catalytic decomposition of N2O, hence contributing to the mitigation of greenhouse gas emission and combating global warming. Supported RhOx catalysts outperform catalysts employing zeolites and composite metal oxides even under challenging conditions involving O2, H2O, and CO2. This study explores the augmentation of Rh/ZrO2 (RhOx supported on monoclinic ZrO2) catalyst efficiency through the addition of palladium (Pd) to yield RhPd/ZrO2. The augmented catalyst demonstrates notable improvements in N2O decomposition under both N2O-only and more realistic conditions (N2O + O2 + H2O + CO2). Various techniques, including high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption spectroscopy, were employed to investigate the structural characteristics of Rh and Pd species on ZrO2. Kinetic studies further delved into the promotional effect, revealing that the introduction of Pd enhanced the catalytic activity of RhOx catalysts by augmenting their thermal reduction capability. This enhancement proved beneficial in facilitating the efficient progression of the rate-determining step for N2O catalytic decomposition, namely the thermal reduction of the catalyst to produce gaseous O2, particularly at low temperatures. These results highlight the potential of Pd-mediated improvements in Rh/ZrO2 catalysts for sustainable and efficient N2O decomposition.

Boosting N2O Catalytic Decomposition by the Synergistic Effect of Multiple Elements in Cobalt-Based High-Entropy Oxides.

Nitrous oxide (N2O) has a detrimental impact on the greenhouse effect, and its efficient catalytic decomposition at low temperatures remains challenging. Herein, the cobalt-based high-entropy oxide with a spinel-type structure (Co-HEO) is successfully fabricated via a facile coprecipitation method for N2O catalytic decomposition. The obtained Co-HEO catalyst displays more remarkable catalytic performance and higher thermal stability compared with single and binary Co-based oxides, as the temperature of 90% N2O decomposition (T90) is 356 °C. A series of characterization results reveal that the synergistic effect of multiple elements enhances the reducibility and augments oxygen vacancy in the high-entropy system, thus boosting the activity of the Co-HEO catalyst. Moreover, density functional theory (DFT) calculations and the temperature-programmed surface reaction (TPSR) with isotope labeling demonstrate that N2O decomposition on the Co-HEO catalyst follows the Langmuir-Hinshelwood (L-H) mechanism with the promotion of abundant oxygen vacancies. This work provides a fundamental understanding of the synergistic catalytic effect in N2O decomposition and paves the way for the novel environmental catalytic applications of HEO.

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.

New insights into the effect of polyvinyl alcohol on Co3O4 spinel oxide catalyst for N2O decomposition

Polyvinyl alcohol (PVA)-assisted precipitation method offered surface modification Co3O4 spinel oxides which were applied to catalytic N2O decomposition. PVA was added in the preparation process and endowed catalysts with changes in surface metal ions valance state properties, i.e. Co2+ ions which served as active centers. Co3O4 adding PVA (Co3O4-P) showed superior performance for catalytic N2O decomposition with a high gas hourly space velocity of 400,000 h−1. Co2+ ion quantities were positively correlated to catalytic performance which was inseparable from PVA superhydrophobicity and reducibility during the preparation process. Moreover, density functional theory (DFT) calculation revealed N2O preferable adsorption on Co2+ sites whether near oxygen vacancies or not, which indirectly affirmed the reason Co3O4-P with superior catalytic N2O decomposition property. Our research gave more evidence to N2O decomposition active sites from atom-scale for Co3O4 spinel oxides and provided a novel pathway for high-performance catalyst preparation.

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.

Roles of Re and Cs Promoters and Organochlorine Moderators in the Synthesis of Ethylene Oxide on Ag‐based Catalysts

AbstractC2H4−O2 reactions form ethylene oxide (EO) on Ag nanoparticles dispersed on α‐Al2O3 and promoted with alkali and other elements, with Re and Cs most frequently used in practice. Traces of alkyl chlorides (e. g., C2H5Cl) and alkanes in much larger amounts are added to reactants to balance the rate of deposition and removal (and the coverage) of Cl adatoms (Cl*) on Ag surfaces. Such Cl adlayers retain Ag surface ensembles that form O2‐derived intermediates that favor EO synthesis, but typically decrease O2 activation rates. A series of Ag/α‐Al2O3 catalysts (with and without Re or Cs) are used here to examine the role of promoters and Cl moderators through an analysis of the effects of reaction conditions and C2H5Cl levels using convection‐reaction constructs and a mechanistic formalism that considers O2 (as chemisorbed O2*) as the reactant in EO synthesis through one electrophilic O‐atom, with the second O‐atom (O*) acting as a unselective nucleophile that must be scavenged by a sacrificial reductant (C2H4 or EO); such channels are precluded by any intervening O2 dissociation events (that form two O*). O2 consumption rates in C2H4−O2 reactions decrease 10‐fold upon exposing Ag/α‐Al2O3 to C2H5Cl, evincing persistent Cl* species that block active sites and require >104 C2H4 oxidation turnovers to be removed. Activation barriers do not change but relative rates of epoxidation versus combustion increase in the presence of this refractory Cl* adlayer, which reduces the number and shrinks the size of available site ensembles without altering their intrinsic reactivity for O2 activation to form O2* but attenuating rates of its subsequent dissociation. Refractory O* adlayers also form on Ag surfaces, as shown by the accumulation of persistent O* species upon exposing reduced Ag particles to N2O. Inter‐atom repulsive forces weaken O* binding and destabilize N2O decomposition transition states to eventually allow stable N2 and O2 evolution for catalytic N2O decomposition, which occurs at landing ensembles formed at interstices of refractory adlayers. Cl* forms denser adlayers than O*, as evidenced by a 10‐fold decrease not only to C2H4−O2 rates but also to N2O stoichiometric and catalytic rates and O* uptakes. The occasional evolution of O2, which forms larger landing ensembles that more readily form 2O* from O2, occurs with higher frequency from O* than mixed O*/Cl* adlayers, and this effect of Cl* to inhibit (O−O)* dissociation is demonstrated in CO probe reaction studies, which show that highly reactive bound dioxygen species are retained to a greater extent when adlayers comprise both Cl* and O*. Re and Cs do not influence the nature of such adlayers but increase and decrease, respectively, the number of acid sites and selectivity losses via EO combustion. Their respective domains may also block a modest fraction of Ag surfaces without consequences on intrinsic O2 activation rates or EO selectivities. The effects of Re beyond those reported here may emerge upon synthetic protocols that alter Re location and Ag−Re intimacy to enable channels which utilize both O‐atoms in epoxidation.

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.

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.

Waste eggshell to valuable Co3O4/eggshell material as an efficient catalyst for catalytic decomposition of N2O under simulated real tail gases

Co3O4 shows excellent catalytic activity for N2O decomposition, in which it is urgently needed to develop novel efficient catalysts/supports with cheap and environmentally-friendly properties. Herein, Co3O4 nanoparticles decorated eggshell catalysts (Co3O4/eggshell-GR, Co3O4/eggshell-IM, and Co3O4/eggshell-DP) were prepared using simple grinding, impregnation, and deposition-precipitation methods, where waste eggshells were used as an effective support and reaction-promoter. The results indicated that the preparation methods significantly influenced the catalytic activity of Co3O4/eggshell catalysts; the highest activity was obtained over the Co3O4/eggshell-DP. The activity of Co3O4/eggshell-DP was comparable to that of pure Co3O4. More importantly, its specific activity was about 7.3 times that of Co3O4 at 400 °C. The examined Co3O4/eggshell-DP also displayed outstanding stability and anti-poisoning property in NO, O2, and/or H2O-containing atmospheres. It was also verified that the excellent activity of Co3O4/eggshell-DP correlated with the unique structure of the eggshell and the close incorporation between CaCO3 and Co3O4. The Co3O4/eggshell-DP catalyst owned abundant Co3O4 nanoparticles, more Co3+ species, and excellent redox performance, promoting the conversion of N2O at a lower temperature. The presence of abundant surface basic sites and a larger amount of oxygen vacancies also facilitated the catalytic efficiency of Co3O4/eggshell-DP.

Insights into reaction pathway induced by d orbital occupancy on cobalt supported boron nitride for N2O catalytic decomposition

Nitrous oxide (N2O), as a typical greenhouse gas, is urgent to be eliminated to address the global climate issue. Developing low-temperature N2O decomposition catalysts is crucial for mitigating greenhouse gas emissions. Herein, we propose a Cobalt-supported boron nitride (Co-BN) catalyst with a low reaction energy barrier (1.37 eV) using density functional theory calculations. The coordination environment is critical to the reaction mechanism and energy barrier, where the CoN3 configuration (Co coordinated with three N atoms) triggers the Eley-Rideal (E-R) mechanism, but the CoB3 configuration (Co coordinated with three B atoms) engenders the Langmuir-Hinshelwood (L-H) mechanism. Fundamentally, the reaction mechanism is dominated by d orbital occupancy. Following the adsorption of *O intermediate, a fully filled d orbital is realized on *O-CoN3, which prevents N2O from bonding with Co, thus following the E-R mechanism through directly interacting with *O specie. Conversely, the partially unoccupied d orbital is identified on *O-CoB3, provinding the bonding site on Co for N2O molecule, thereby leading to the L-H mechanism. Our work provides a novel N2O decomposition catalyst theoretically, and the insights into the relationship between d orbital occupancy and the reaction mechanism, would pave a new avenue for the design of N2O decomposition catalysts.

Highly effective and energy-saving adsorption-microwave catalytic decomposition of NO with novel high-adsorption-capacity adsorbent in a two-stage fixed-bed reactor

It is a great challenge to achieve high efficiency and low energy consumption denitrification without adding reducing agent at low temperature. Herein, we developed MgCo2O4-BaCO3/AC carbon-based composites as novel and cheap adsorbents with high adsorption capacity to fill the first section of two-stage fixed-bed reactor to form adsorption bed, and MgCo2O4-40%BaCO3 as catalyst was filled in the second section as catalyst bed. Significantly, under the condition of excess O2, the adsorption capacity of 20%MC-0.5Ba/AC for NO was as high as 40.2 mg/g, and the conversion of adsorbed NO was as high as 99.7% under microwave irradiation at 250 °C. The denitrification efficiency of the two-stage fixed bed reactor was much higher than that of the one-stage fixed bed reactor. The energy efficiency of adsorption-decomposition method was 14 times higher than that of direct decomposition method. Interestingly, the activated carbon was not consumed during the whole reaction process, so no secondary pollution such as CO and CO2 was produced. More importantly, despite the presence of SO2, CO2 or H2O in the inlet gas, 20%MC-0.5Ba/AC still showed excellent adsorption capacity for NO, and the absorbed NO could be successfully decomposed, demonstrating excellent resistance to SO2, CO2 and H2O. This work presents a new route for denitrification technology with high efficiency, low energy consumption and no secondary pollution, and provides guidance for rational design of adsorbents with high adsorption capacity for NO.

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.

Influence of Co3O4-based catalysts on N2O catalytic decomposition and NO conversion.

This study investigated the effect of different Co3O4-based catalysts on the catalytic decomposition of nitrous oxide (N2O) and on nitric oxide (NO) conversion. The experiments were carried out using various reaction temperatures, alkaline solutions, pH, mixing conditions, aging times, space velocities, impregnation loads, and compounds. The results showed that Co3O4 catalysts prepared by precipitation methods have the highest catalytic activity and N2O conversion, even at low reaction temperatures, while the commercial nano and powder forms of Co3O4 (CS) have the lowest performance. The catalysts become inactive at temperatures below 400°C, and their activity is strongly influenced by the mixing temperature. Samples without stirring during the aging process have higher catalytic activity than those with stirring, even at low reaction temperatures (200-300°C). The catalytic activity of Co3O4 PM1 decreases with low W/F values and low reaction temperatures. Additionally, the catalyst's performance tends to increase with the reduction process. The study suggests that cobalt-oxide-based catalysts are effective in N2O catalytic decomposition and NO conversion. The findings may be useful in the design and optimization of catalytic systems for N2O and NO control. The results obtained provide important insights into the development of highly efficient, low-cost, and sustainable catalysts for environmental protection.

A novel fluidized-bed-electrode solid-oxide-fuel-cell reactor for N2O catalytic decomposition

Global warming potential (GWP) of N2O is 310 times that of CO2. However, conventional solid oxide fuel cell (SOFC) cathode catalytic N2O decomposition has been observed to have a low conversion rate, leading to uneven temperature distribution on the cathode surface. To address this issue, we proposed a novel gas–solid phase fluidized bed catalytic electrode for N2O decomposition in a SOFC system. The fluidized bed material was prepared using cerium oxide particles coated with lanthanum, strontium, and iron (CeO2-LSF). The N2O conversion rate was 99.78% at 720 °C. By assisting particle fluidization with argon, compared to the case of fixed bed electrode, the peak power density improved by a maximum of 39.86% at 670 °C. This improvement was due to mass transfer enhancement by particle fluidization, thereby reducing the concentration polarization of the SOFC. Furthermore, the maximum temperature difference inside the reactor decreased significantly from 92 °C to 42 °C when the cathode particles were fluidized. The reactor can achieve high-efficiency decomposition of N2O while simultaneously improving fuel cell power density and operational reliability.

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.

Unravelling the Effect of Alkali Metal Deposition on Co3O4 for Catalytic Decomposition of N2O

AbstractIn this paper, the effect of alkali metal deposition on the activity of x‐Co3O4 (x=Na, K, Rb, Cs) catalysts for the N2O catalytic decomposition was systematically explored by DFT calculation and various experimental characterization methods. The results demonstrated that the deposition of alkali metal Na improved the activity of the Na‐Co3O4 catalyst for N2O catalytic decomposition at low temperatures. By contrast, the deposition of other alkali metals (K, Rb and Cs) suppressed the catalytic decomposition of N2O perceptibly. Analysis of the results of XRD, FT‐IR, SEM, TEM, XPS, O2‐TPD and H2‐TPR characterization of x‐Co3O4 catalysts showed that the deposition of alkali metals did not affect the morphology and structure of the catalysts. However, it affected the chemical environment around the Co ion in the x‐Co3O4 catalyst, where the deposition of alkali metal Na not only facilitated the reduction of Co3+ to Co2+, but also promoted the surface decomposition step of N2O (i. e., the oxidation of Co2+ to Co3+ by giving electrons) at low temperatures, indicating that alkali metal Na improved the electron donating capability of the catalyst active center and enhanced the performance of the Na‐Co3O4 catalyst for the DCD of N2O at low temperatures. The deposition of other alkali metals did not show the same results as that of alkali metal Na, indicating that the promotion of different alkali metals was different and would directly affect the catalytic effect. At low temperatures, the catalytic activity of catalysts deposited with the alkali metal Na was greater than that of catalysts deposited with other alkali metals.