NO Decomposition Activity Research Articles

Diverse effects of ferromagnetic-paramagnetic phase transition on the activity and selectivity of ferromagnetic catalysts

Tuning the catalyst’s activity and selectivity is usually achieved by modifying the electronic structure through strategies such as alloying, doping, strain, and ligand modification, but inevitably accompanied by geometric structure changes of catalysts. It is challenging to modify a catalyst’s electronic structure without changing its geometric structure. Recent studies found that the second-order ferromagnetic to paramagnetic (FM-PM) phase transition could promote catalytic performance without altering the geometric structures of active sites, which was also known as the magneto-catalytic effect (MCE). However, the understanding of the MCE is still incomplete. Herein, we conducted systematic density functional theory (DFT) calculations to clarify the complex reaction mechanisms for conversions of nitrogen-containing small molecules on both FM and PM Ni (111) surfaces. Our microkinetic modeling (MKM) results demonstrate that FM-PM phase transition promotes the N2O decomposition activity of FM Ni catalyst but decreases its activity for NO decomposition while showing a negligible influence on the activity of ammonia decomposition. These results indicate the promotion, inhibition, and disappearance mechanisms of MCE on the catalytic activity, which further changes the selectivity of different products. We anticipate the MCE will work as an effective strategy for fine-tuning the activity and selectivity of ferromagnetic catalysts in heterogeneous catalysis, providing an extra basis for rational catalyst design.

Improved activity and significant O2 resistance of Cs doped Co3O4 catalyst for N2O decomposition

Csx-Co3O4 catalysts with excellent low temperature activity and oxygen resistance for N2O decomposition were prepared using a citric acid complexation method. The mechanism of Cs doping on Co3O4 was systematically investigated by characterization techniques such as XRD, Raman, N2 adsorption, HR-TEM, XPS, H2-TPR, O2-TPD, and combined with DFT calculation methods. The results indicated that the presence of Cs inhibited the growth of Co3O4 grains and increased the specific surface area. Cs doping significantly increased the number of exposed oxygen vacancies, which tended to form around CoO4 (Co2+) tetrahedral sites replaced by Cs, following the trend Evac(1 1 1) <Evac(1 1 0) <Evac(1 0 0). Furthermore, the interaction between Cs and Co enhanced the electron donating ability of Co, promoted the reduction of Co3+ to Co2+ and weakened the Co-O bond. Among all the samples, the one with a Cs/Co molar ratio of 0.1 exhibited the highest activity. At 275 °C, the Rs of Cs0.1-Co3O4 was 39.5 times that of pure Co3O4. More importantly, Cs0.1-Co3O4 exhibited excellent oxygen resistance, achieving a high N2O conversion rate of 94 % under conditions of 300 °C and 20 % O2.

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.

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.

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.

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.

Effects of Ni doping on structural, magnetic and catalytic properties of copper ferrite

The aim of this work was to obtain information about the influence of small quantities of Ni2+ ion on the structural and magnetic properties of the tetragonally distorted of Cu1−xNixFe2O4 series (with x = 0.00, 0.05, 0.1, and 0.15 respectively). The tested ferrite system was synthesized by combustion of citrate–nitrate precursors. The synchrotron X-ray diffraction measurements determined the phase transition temperatures (tetragonal → cubic) of all samples. The change of structures under the influence of temperature shows a phase transition in the range of 390 – 400 °C for x = 0.00, 330 – 370 °C for x = 0.05, 210 – 330 °C for x = 0.1 and 140 – 210 °C for x = 0.15, respectively. The initial phase transition temperature decreases linearly with the decreasing c/a ratio of the crystallographic lattice parameters for the Cu1−xNixFe2O4 oxides. Hysteresis measurements were made to determine the saturation magnetization (MS) and coercive field (µ0Hc) of the samples. The values of magnetic moments at room temperature determined from magnetization measurements are very similar to those obtained from theoretical x-ray diffraction calculations. Magnetic moment values per formula unit are estimated to range from 1.16 μB to 1.5 μB. It was found that the catalytic activity of N2O decomposition of samples increases with increasing nickel content.

Boosting N2O Decomposition by Fabricating the Cs-O-Co Structure over Co3O4 with Single-Layer Atoms of Cs.

Developing effective catalysts for N2O decomposition at low temperatures is challenging. Herein, the Cs-O-Co structure, as the active species fabricated by single-layer atoms of Cs over pure Co3O4, originally exhibited great catalytic activity of N2O decomposition in simulated vehicle exhaust and flue gas from nitric acid plants. A similar catalytic performance was also observed for Na, K, and Rb alkali metals over Co3O4 catalysts for N2O decomposition, illustrating the prevalence of alkali-metal-promotion over Co3O4 in practical applications. The catalytic results indicated that the TOF of Co3O4 catalysts loaded by 4 wt% Cs was nearly 2 orders of magnitude higher than that of pure Co3O4 catalysts at 300 °C. Interestingly, the conversions of N2O decomposition over Co3O4 catalysts doped by the same Cs loadings were significantly inhibited. Characterization results indicated that the primary active Cs-O-Co structure was formed by highly orbital hybridization between the Cs 6s and the O 2p orbital over the supported Co3O4 catalysts, where Cs could donate electrons to Co3+ and produce much more Co2+. In contrast, the doped Co3O4 catalysts were dominated by Cs2O2 species; meanwhile, CsOH species was generated by adsorbed water vapor led to a significant decrease in catalytic activity. In situ DRIFTS, rigorous kinetics, and DFT results elaborated the reaction mechanism of N2O decomposition, where the direct decomposition of adsorbed N2O was the kinetically relevant step over supported catalysts in the absence of O2. Meanwhile, the assistance of adsorbed N2O decomposition by activated oxygen was observed as the kinetically relevant step in the presence of O2. The results may pave a promising path toward developing alkali-metal-promotion catalysts for efficient N2O decomposition.

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

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

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.

Enhancement of catalytic N2O decomposition by modulating oxygen vacancies over Cu/Ce1-XYX catalysts

We reformed Cu supported on Ce-Y via CeO2-Y2O3 solid solution to improve the activity in catalytic N2O decomposition. Catalysts with different Ce/Y molar ratios were used in all experiments and analytic techniques. Cu/Ce0.5Y0.5 achieved the highest activity. Up to Ce/Y molar ratio = 1, the activation energy required for N2O decomposition decreased but markedly increased when the Y2O3 lattice was the support by an excess of Y loading. The number of sites accessible to N2O and surface oxygen vacancies increased with Y species loading. However, the activity of Cu/Ce0.1Y0.9, Y2O3-based catalysts, decreased due to the difficulty of releasing O2 from its strong affinity with O2. Proper incorporation of Ce-Y enhanced the N2O decomposition activity by modulating the number of oxygen vacancies while maintaining the CeO2 lattice.

Regulating local coordination environment of rhodium single atoms in Rh/CeO2 catalysts for N2O decomposition

Rh single atom catalysts (SACs) have been insensitively investigated recently due to the maximum utilization efficiency of Rh, one of the most expensive precious metals. Although great efforts have been made in the development and application of Rh SACs, there are few reports on the precise control of the local coordination environment of Rh single sites on CeO2 and their catalytic performance for N2O decomposition. Herein, Rh/CeO2 catalysts with different Rh–O coordination numbers (CNs) were successfully prepared using different CeO2 supports and a simple incipient wetness impregnation (IWI) method. It is observed that the Rh/CeO2 catalyst with slightly higher CN of Rh–O (Rh/CeO2-H) prepared from CeO2 shows much higher N2O decomposition activity than the catalyst with lower CN of Rh–O (Rh/CeO2-L) obtained from Ce(OH)x. The Rh species within Rh/CeO2-H are found to be more reactive than those within Rh/CeO2-L, which can better facilitate the O2 desorption once formed during N2O decomposition. In addition, more surface oxygen vacancies are present on Rh/CeO2-H than on Rh/CeO2-L, well explaining the superior N2O adsorption and activation capability on the former catalyst. It is concluded that more abundant oxygen vacancies and reactive Rh single atom sites with slightly higher CN of Rh–O and significantly higher reducibility altogether contribute to the superior N2O decomposition activity on the Rh/CeO2-H catalyst.

Efficient catalytic decomposition of N2O over Cd-doped NiO in the presence of O2

A series of Cd-doped NiO catalysts were prepared and tested in the N2O catalytic decomposition reaction. In comparison with NiO, it was found that the Cd0.04Ni catalyst showed higher N2O decomposition activity in the temperature range of 300–450 °C with or without O2, and lower activation energy (77.8 kJ mol−1). The incorporation of Cd into the NiO lattice was verified by X-ray diffraction (XRD) patterns and Raman spectra. This led to the distortion of the original NiO structure and weakened the Ni-O bond. X-ray photoelectron spectroscopy (XPS) results showed that compared with NiO and CdO, Cd0.04Ni possessed higher Ni2+ and Cd(n+1)+ contents, which might have been induced by the electron transfer behavior between CdO and NiO. A possible mechanism for active site regeneration and O2 desorption over Cd0.04Ni was proposed. The Cd0.04Ni catalyst also exhibited good resistance to NO and O2.

Analysis of N2O reduction by components of red mud in bubbling fluidized bed

Circulating fluidized bed (CFB) technology is developing rapidly, but there is no effective treatment measure for N2O emission. Based on the catalytic theory of metal oxides for N2O, the catalytic performance and apparent activation energy of red mud and its main components for N2O decomposition in gas mixture were measured in a bubbling fluidized bed. The decomposition rate and catalytic rate of different materials were compared. The properties of the materials were similar to those of red mud. The main oxides of red mud were proportioned, and the N2O decomposition experiment was carried out by changing their proportions. The decomposition effect of N2O by various materials in coal-fired process was tested. It is found that all kinds of additives can accelerate the decomposition of N2O with different degrees, but the effect on NO is not significant. When the initial amount of N2O is the same, the catalytic activity of red mud for N2O decomposition is higher than that of single oxide and mixed oxide with different proportions in red mud. The order of catalytic activity for N2O decomposition is: Red mud > CaO > Al2O3 > Fe2O3 > SiO2 > MgO ≈ TiO2. For ammonia injection process, all additives can promote the decomposition of N2O and NO. Compared with other materials, red mud has stronger N2O decomposition ability, lower recovery rate and better economic performance. Iron-containing components can accelerate N2O decomposition, but increase the emission of NO. As a bed material and additive, Al2O3 can achieve better balance between N2O and NO.

Enhancement of Cs on Co3O4 for N2O Catalytic Decomposition: N2O Activation and O2 Desorption

In this work, a series of cesium (Cs) modified metal oxide (Co3O4, CuO, Mn2O3, and NiO) catalysts were synthesized and investigated for N2O catalytic decomposition. More than 95% N2O conversion was obtained with the Cs-supported Co3O4 (Cs/Co) catalyst at 300 °C, but only a slight increase or even suppression was obtained with the other catalysts. The activation energy (Ea) varied significantly for Cs modified catalysts. It was found that both of N2O adsorption–dissociation (from N2O-TPD) and O2 desorption capacities (from O2-TPD) were highly correlated with the N2O decomposition activity. Highly optimized N2O activation and O2 desorption capacities contributed to the boosting performance of the Cs/Co catalyst. Moreover, the improved electron transfer property inferred from H2-temperature-programmed reduction and X-ray photoelectron spectroscopy was likely to facilitate the reaction processes and promote N2O catalytic decomposition performance.

Novel cobalt‐doped ZrSnO4 catalysts for direct nitrous oxide decomposition

AbstractNovel ZrSn1−xCoxO4−δ catalysts for the direct decomposition of nitrous oxide (N2O) were synthesized using a co‐precipitation method. Metastable ZrSnO4 with an α‐PbO2‐type structure was used as the mother solid because of its interstitial open spaces derived from its lattice distortion that may be effective for N2O adsorption. The doping of Co2+/3+ into the ZrSnO4 lattice improved the N2O decomposition activity, likely owing to the enhancement of the redox properties and the increase in the number of oxygen vacancies. Among the prepared catalysts, Zr1.17Sn0.73Co0.10O4−δ exhibited the highest activity decomposing N2O completely decomposed at 550°C. In addition, the Zr1.17Sn0.73Co0.10O4−δ catalyst showed high durability in the presence of CO2, O2, and H2O vapor.

Taming the Redox Property of A0.5Co2.5O4 (A = Mg, Ca, Sr, Ba) toward High Catalytic Activity for N2O Decomposition

Nitrous oxide (N2O) originating from the combustion of fossil fuels causes serious environmental issues. The design and construction of a catalyst with high performance for the removal of N2O remains challenging. Herein, a series of alkaline-earth metal-modified A0.5Co2.5O4 (A = Mg, Ca, Sr, Ba) catalysts were initiated by a hydrothermal protocol, and their catalytic activities for N2O decomposition were systematically investigated by experimental and density functional theory calculation. The results reveal that the doping of alkaline-earth metals significantly affects the morphology, structure, active oxygen species, oxygen vacancy, and redox property and thereafter the catalytic activity of A0.5Co2.5O4 for N2O catalytic decomposition. The introduction of alkaline-earth metals (A = Ca, Sr, Ba) considerably promoted the reduction of Co3+ to Co2+, thereby improving the electron-donating ability and oxygen vacancy number and thereafter weakening the Co–O bond. As a result, the catalytic activity of N2O decomposition distinctively enhanced. Among them, Ba0.5Co2.5O4 shows optimal N2O decomposition performance by virtue of its outstanding active oxygen species and excellent redox property. However, the doping of Mg suppresses the electron-donating ability of Mg0.5Co2.5O4 and thereafter the catalytic activity for N2O decomposition. Therefore, this work may shine light on the understanding of N2O decomposition over alkaline-earth metal-modified Co-based oxides.

Promotion effect of rare earth elements (Ce, Nd, Pr) on physicochemical properties of M-Al mixed oxides (M\u2009=\u2009Cu, Ni, Co) and their catalytic activity in N2O decomposition

A series of M-AlOx mixed oxides (M = Cu, Co, Ni) with the addition of high loadings of rare earth elements (REE, R = Ce, Nd, Pr; R0.5M0.8Al0.2, molar ratio) were investigated in N2O decomposition. The precursors were prepared by coprecipitation and subsequent calcination at 600 °C. The obtained mixed metal oxides were characterized by X-ray diffraction with Rietveld analysis, N2 sorption, and H2 temperature-programmed reduction. Depending on the nature of REE and the initial M-Al system, R cations could be separately segregated in oxide form or coordinated with the transition metal cations and form mixed structures. The addition of Ce3+ consistently led to nanocrystalline CeO2 mixed with the divalent oxides, whereas the addition of Nd3+ or Pr3+ resulted in the formation of their respective oxide phases as well as perovskites/Ruddlesden–Popper phases. The presence of REE modified the textural and redox properties of the calcined materials. The rare earth element-induced formation of low-temperature reducible MOx species that systematically improved the N2O decomposition on the modified catalysts compared to the pristine M-Al materials by the order of Co > Ni > Cu. The Ce0.5Co0.8Al0.2 catalyst revealed the highest activity and remained stable (approximately 90% of N2O conversion) for 50 h during time-on-stream in 1000 ppm N2O, 200 ppm NO, 20 000 ppm O2, 2500 ppm H2O/N2 balance at WHSV = 16 L g−1 h−1.

The correlation of NO chemisorption adsorption with its directly catalytic dissociation pathway on β-MnO2(1 1 0) and (1 0 1) surfaces

MnO2-based oxide catalysts have recently drawn so much attention owing to its good catalytic activity for NOx direct catalytic decomposition at low-temperature. As the reaction mechanism of NO direct catalytic decomposition on different MnO2 surfaces is not yet clear, it is important to understand the influence of different crystal surfaces of β-MnO2 on catalytic activity for NO decomposition. The correlation of NO chemisorption with its dissociation pathways on β-MnO2(110) and (101) surfaces are investigated based on density functional theory (DFT) with Vienna Ab-initio Simulation Package (VASP). The calculation results have shown that NO prefers to be adsorbed on β-MnO2(110) instead of β-MnO2(101) surface. The analysis results of density of states and differential charge density indicate that the interaction between NO and β-MnO2(110) surface is stronger and the adsorbed NO had more charge transfer with β-MnO2(110) surface. The effective activation energies of the possible NO dissociation pathways on the β-MnO2(110) and (101) surfaces are 2.57 and 3.07 eV, respectively. The lower energy barrier on β-MnO2(110) must be associated with the bridge adsorption of NO and more electrons transfer from NO to the surface, which is conducive to the breaking of N-O bond.