NO Oxidation Rate Research Articles

Synthesis of La1-xSrxCoO3-δ and its catalytic oxidation of NO and its reaction path

The oxidation rate of NO to NO2 is a critical parameter in the removal of NOx within selective catalytic reduction (SCR) systems. LaCoO3-δ is a kind of potential catalyst to enhance the oxidation of NO to NO2, it may offers an economic and stable alternative to noble metal catalysts, particularly at elevated temperatures. This study aimed to enhance the catalytic efficiency of LaCoO3-δ through strontium (Sr) doping. La1-xSrxCoO3-δ (with varying x values of 0.1, 0.2, 0.3, 0.4) was synthesized using a sol-gel method. La1-xSrxCoO3-δ exhibited superior NO oxidation catalytic activity compared to LaCoO3-δ, with the most notable enhancement observed at x = 0.3 (84 % conversion). This improvement can be attributed to the substitution of La3+ with Sr2+, which induces lattice distortion and charge imbalance, thereby creating more oxygen vacancies that enhance the catalytic oxidation capability of La1-xSrxCoO3-δ. However, it's important to note that an excessive amount of Sr can result in the formation of SrCO3 deposits on the surface of La1-xSrxCoO3-δ, thereby diminishing its catalytic oxidation performance. The catalytic oxidation reaction behavior adhered most closely to the O2-adsorbed E-R model, the surface defects in La1-xSrxCoO3-δ playing a pivotal role in the catalytic reaction.

Plasma catalysis: separating plasma and surface contributions for an Ar/N2/O2 atmospheric discharge interacting with a Pt catalyst

Atmospheric pressure non-equilibrium plasmas can form nitrogen oxide (NO x ) compounds directly from nitrogen and oxygen without a catalyst, and at lower catalyst temperatures than would be possible without plasma. In this work, the oxidation of plasma-produced NO from an Ar/N2/O2 non-equilibrium atmospheric-pressure plasma-jet (APPJ) over a platinum-on-alumina powder catalyst was investigated with in-situ infrared spectroscopy. Products downstream of the catalyst bed were analyzed along with catalyst surface species. The catalyst was exposed to plasma at both constant temperature and a cyclic temperature ramp in order to study long-lasting and transient surface changes. Primary incident reactive species to the catalyst were assessed to be NO and O3. Pt-Al2O3 at 350 °C increased oxidation of NO relative to Al2O3 or an empty chamber. The surface state of Pt-Al2O3 evolves during plasma-effluent exposure and requires upwards of 20 min exposure for stabilization compared to Al2O3. Once stable surface conditions are achieved, thermal cycling reveals a repeatable hysteresis pattern in downstream products. At low temperature, oxygen and NO x accumulate on the catalyst surface and react at elevated temperatures to form NO2. Increasing plasma power and O2:N2 ratio increases the hysteresis of the heating relative to the cooling curves in the pattern of NO2 formation. The limitation on NO oxidation at high temperatures was assessed to be Pt-O which is depleted as the catalyst is heated. Once stored species have been depleted, NO oxidation rates are determined by incoming reactants. Two overlapping NO oxidation patterns are identified, one determined by surface reactants formed at low temperature, and the other by reactants arriving at the surface at high temperature. The plasma is responsible for providing the reactants to the catalyst surface, while the catalyst enables reaction at high temperature or storage at low temperature for subsequent reaction.

Undercovering the role of physicochemical properties of amides in two-phase absorbent systems for ship exhaust pollutant removals

The use of two-phase absorbents containing amides to treat ship pollutants is a new research solution that can achieve high NO oxidation rates and NO2 absorption rates. This paper studies the physicochemical properties of five different amides and their relationship with the desulfurization and denitrification processes. It was found that nitrous acid molecules undergo an isomerization rearrangement in the amide and combine in a more stable form during the NOx absorption process. The polarity and viscosity of the amide are more critical than the min ESP value in removing pollutants. The high polarity and low viscosity of DBA (N,N-Dibutylacetamide) provide dual advantages, facilitating the interaction between the organic and aqueous phases, as well as enhancing the mass transfer process and the combination of an inorganic acid. The system containing DBA achieved removal efficiencies of 99.6% for SO2, 86.33% for NO, and 86.3% for NOx in 10 min. Overall, this study provides valuable insights into the use of organic-containing two-phase absorbents to reducing ship exhaust pollution.

Schottky construction of bimetallic Au-Cu alloy@TiO2 hollow nanoboxes embedded optical switch for enhancing photocatalytic and selective adsorption activities via one-pot deposition-precipitation strategy

One-pot soft integration strategy based on wet chemistry via a simple in situ deposition-precipitation approach has been developed to fabricate series of bimetallic Au-Cu alloy@TiO2 hollow nanoboxes (THB) embedded optical switch. The bimetallic Au-Cu alloys were embedded into the nanodevice through Schottky junctions. This embedded optical switch could exhibit excellent photocatalytic performance. Under simulated sunlight irradiation, Au-Cu4:3 @THB nanodevice exhibited the photodegradation rate of RhB was of 99.4 % in 150 min, which was 3.0 times higher than that of THB. The oxidation rate of NO reached 27.0 %, 2.3 times that of THB. The enhanced photocatalytic activity could mainly be attributed to Au-Cu alloy SPR effects; the photoreactivity of the nanodevice was greatly improved after modification with bimetallic Au-Cu. Under dark conditions, the RhB adsorption rate of bimetallic Au-Cu4:3 @THB nanodevice reached 98.6 %, which was 6.1 times higher than that of THB. As the adsorption effect test of mixed dyes (MB/MO and RhB/MO), after 5 h of adsorption, the adsorption capacity of cationic dyes was 3.1 times that of anionic dyes, it was concluded that the bimetallic Au-Cu4:3 @THB optical switch had an excellent selective adsorption effect. This was due to the large surface area and mesoporous structure of the adsorbent, good electron transport structure, and the formation of a galvanic cell after adding dyes. This research provides a promising catalytic material with optical switch for environmental restoration and protection. It has broad application prospects in photocatalytic degradation, photocatalytic oxidation and adsorption of organic pollutants.

Preparation of TiO2/graphene oxide and their photocatalytic properties at room temperature

TiO2/GO with different graphene oxide (GO) composite ratios were prepared by hydrothermal method and characterized by SEM, TEM, XRD, UV-vis, XPS, Raman and photocurrent. The results show that both TiO2 and GO/TiO2 crystal are anatase type. Part of GO is reduced to the reduced graphene oxide (RGO), properties of which are closer to that of graphene, when GO is prepared by hydrothermal reaction with butyl titanate. And such transformation is conducive to photoelectron transfer. Compared with pure TiO2, the composite TiO2/GO catalyst has a smaller grain size and a higher ratio of adsorbed oxygen/lattice oxygen, which is beneficial to the oxidation of NO. Moreover, lower band gap enhances the abilities of absorbing visible light and the photoelectron response over TiO2/GO catalyst. Therefore, the catalyst exhibits more excellent photocatalytic performance. The photocatalytic denitration performance of the composites was evaluated under visible light. When the GO composite ratio is 1.5%, the catalyst possesses the optimal photocatalytic denitration performance. When the ratio of ammonia to nitrogen is 1:1, the denitration efficiency can reach as high as 88.6%, which is 30% higher than that of self-made unmodified TiO2 and 40% higher than that of V-Ti-W catalyst. The anti-interference ability is significantly stronger than that of commercial V-Ti-W catalysts. It is concluded, from the mechanism analysis, that the oxidation rate of NO plays a key role in the process of photocatalytic denitration, and the presence of ammonia can accelerate the reduction of NO2.

Influence of air temperature on air composition in Moscow

Empirical relations between T and surface concentrations of CO2 and five minor air gases have been studied on a base of hourly data during 12 years. In wide range -6…+15 °C significant changes of minor gases are absent. Real tendencies are increase of O3 and, vice versa, fall of NO and NO2 with increasing T from +15.+17 to +38 °C. Both effects are a consequence of unstable stratification that enhances vertical mixing. In cool weather -7.-18 °C O3 falls whereas nitrogen oxides grow with decreasing T due to frequent inversions and slowing down the NO oxidation rate. At an even lower temperature up to -30 °C NO and NO2, vice versa, decrease with decreasing T – probably, due to strong cold advection of clean Arctic air. Unlike minor gases, CO2 decreases with increasing T up to 25 °C due to photosynthesis intensification from winter to summer. Seeming growth of CO at T>27 °C is fully explained by smoky haze during heat waves in 2010 and 2002. The CO2 growth in hot weather is also created by heat stress of trees. Thus, except only oxidation rate, any influence of T is indirect as a result of stratification, photosynthesis, smoky haze, advection, etc.

Enhanced adsorption of NO onto activated carbon by gas pre-magnetization

The NO removal efficiency was relatively low in the traditional activated carbon adsorption process. In this work, a gas pre-magnetization and activated carbon adsorption process was developed to enhance the adsorption of NO onto activated carbon. In this innovative and green process, the mixed gas was magnetized in the external magnetic field and then absorbed by activated carbon. The results indicated that the maximal removal rate of NO could be increased from 75.0% to 89.5%, and the NO adsorption capacity of commercial activated carbon in one hour elevated from 2.28 to 2.60 mg/g when the magnetic induction intensity of external magnetic field increased from 0 T to 2 T. The strengthening mechanism of the gas pre-magnetization was investigated. It was found that magnetic field could elevate the oxidation rate of NO by 11.4% and thus promote the physical adsorption of NO onto activated carbon. External magnetic field could increase the reaction activity of NO and promote the chemical reaction between NO and some functional groups (CO, CO and COOH) on the activated carbon and thus promote the chemisorption process of NO.

Numerical investigation on combustion and NOx formation characteristics under deep-staging conditions within a cyclone barrel

Numerical investigation on combustion and NOx distribution characteristics of coal within a cyclone barrel under deep-staging conditions was conducted. Char conversion model and NOx formation model with refined NO heterogeneous reduction mechanism and oxidation rate of HCN suitable for cyclone barrel were implemented and validated with experimental data. The maximum deviations between the predicted and experimental values of NO and CO concentrations are 12.1% and 18.6% respectively under various stoichiometric ratios. Based on the refined models, the NO distribution in cyclone barrel under deep-staging condition is obtained. In the cyclone barrel, the concentration of NOx is higher in the primary-air-controlled and near-wall zones, which hinders further NOx reduction. The appropriately delayed secondary air supply can avoid the centralized supply of O2 and form a reducing atmosphere region in the primary-air-controlled zone, which greatly reduces the initial formation of NOx. In addition, the central zone of the cyclone barrel is the core region for NOx reduction. The area of the central zone with a strong reducing atmosphere can be significantly enlarged by increasing the velocity of secondary air. The NOx formation in cyclone barrel drops by 26.5% under deep-staging condition when the secondary air velocity increases from 20 m/s to 50 m/s. Finally, the oxygen-enriched and deep-staging technology is applied to the cyclone barrel. An ultra-low NOx formation in cyclone barrel is achieved. When the O2 concentration of secondary air increases from 0.21 to 0.40, the NOx formation drops by 64.1% under deep-staging condition. Moreover, the elevated flue gas temperature with O2 enriched in cyclone barrel makes it more suitable for the safe operation of slag tapping cyclone barrel.

Effect of Gas Components and Particulate Matter on the Conversion of Nitric Oxide by Dielectric Barrier Discharge

The conversion of nitric oxide by dielectric barrier discharge (DBD) in different reaction gases (O2, H2O, Ar, and N2) was studied. In the N2/O2 system, N and O could react to form NO; consecutively, extra O would oxidize NO to form NO2. Increase of oxygen content would promote the generation of NO, and the highest concentration of NO2 could be obtained with different oxygen contents at specific energy inputs (SEIs) of 1200 or 1440 J/L. In the N2/O2/NO system, the oxidation and reduction of NO took place simultaneously to form NO2 and N2, and NO was mainly removed by reduction when the oxygen content was lower than 6 vol %. In comparison, in the Ar/O2/NO system, NO was mainly oxidized to NO2. However, when the oxygen content exceeded 12 vol %, the increase of the SEI between 960 and 1440 J/L will increase the temperature of the DBD reactor, resulting in the restrain of the NO oxidation rate. In the SO2/N2/O2/NO system, SO2 could be oxidized by O radicals in the discharge region, leading to the restrain of NOx generation. In the H2O/N2/O2/NO system, H2O could promote the oxidation of NO so that NO conversion could reach 100% at 18 vol % O2 content. In the system of particulate matter/N2/O2/NO, particles would change the parameters in the discharge region and promote the production of N and O radicals, leading to the concentrations of NO2 and NOx being higher than those in the N2/O2/NO system. When the oxygen content was lower than 6 vol %, the conversion of NO reached 100% at 960 J/L. N2O formed in all systems as a byproduct of NO conversion by DBD. With the increase of the SEI, part of N was oxidized, resulting in the increase of NOx in all the systems containing N2.

Simultaneous removal of SO2, NOx and Hg0 by O3 oxidation integrated with bio-charcoal adsorption

Simultaneous removal of SO2, NOx and Hg0 using O3 and corn stalk bio-charcoal (CR)/coconut shell activated carbon (CS) was compared in a fixed bed. The effects of temperature, adsorption time and ratio of O3/NO on the removal efficiency of NO, Hg0 and SO2 by CR/CS were studied, and the CR and CS was characterized and analyzed. The results indicated that the oxidation rate of NO and Hg0 increased with the increase of O3/NO ratio, while the oxidation rate of SO2 first increased and then decreased slightly. The increase of temperature inhibits the oxidation of NO but promotes the oxidation of Hg0 and SO2. At 140°C and O3/NO ratio was 1.4, the oxidation rate of NO, Hg0 and SO2 is 99%, 78.6% and 3.5%, respectively. As O3/NO ratio increased from 0.4 to 1.4, the removal efficiency of CR for NOx increased from 4.6% to 93%, and CS increases from 4.5% to 79%. CR and CS can reduce part of NO2 and increase NO concentration at the outlet. NOx adsorption performance on CR is relatively better, while those of Hg0 and SO2 on CS are relatively stronger. CS has stronger physical adsorption capacity than CR. The relative content of oxygen-containing functional groups C-O and C=O on the surface of CR is higher than that of CS, while its relative content of COOH and O=C-O is lower.

A modeling and experimental study on hydrothermal aging deactivation of NO oxidation activity on Pt-Pd catalyst

A state-of-the-art Pt-Pd catalyst was hydrothermally treated at different conditions to investigate hydrothermal stability of NO oxidation. NO oxidation reactor data was collected on catalysts that have been hydrothermally treated at temperatures ranging from 550 °C until 1100 °C. NO oxidation activity was observed to decrease with increase in aging duration at all the aging temperatures. A global kinetic model of NO oxidation was used to estimate the change in NO oxidation rate when subjected to different hydro-thermal aging conditions. Model estimated normalized rates at multiple hydro-thermal aging conditions were used to develop a hydro-thermal aging model of NO oxidation. A deactivation Model with Residual Activity (DMRA) was developed to capture the impact of hydrothermal aging temperature and duration on NO oxidation activity. A global kinetic model that accounts for change in PGM oxidation state during NO oxidation has also been presented.

The roles of Brønsted acidity in low-temperature catalytic oxidation of NO over acidic zeolites with H2O2

In this study, low-temperature catalytic NO oxidation with H2O2 over Na- and H-exchanged Y and ZSM-5 zeolites was investigated at 140 °C which is the average exhaust temperature of coal-fired power plant. Fast catalytic NO oxidation rates were observed over H-zeolites, and catalytic activity was proportional to the amount of Brønsted acid sites. HZSM-5 and HY zeolites show 65% and 95% NO removal efficiency, respectively, but the catalytic stability of HY was lower than HZM-5 due to partial dealumination during the reaction. In-situ DRIFTS analysis showed that NO+ species coordinated at framework sites played a direct role in the catalytic NO oxidation. Moreover, the possible reaction pathway was proposed to elucidate the mechanism of NO oxidation with H2O2 catalyzed over Brønsted acid sites. The effect of reaction temperature, H2O2 concentration, H2O2 flow and SO2 concentration on NO oxidation were investigated over H-zeolites. The experimental results indicated that the NO removal efficiency was increased with the increase of H2O2 concentration, but decreased with the increase of SO2 concentration. The NO removal efficiency first increased and then decreased with the increase of H2O2 flow and reaction temperature.

Electronic parameters in cobalt-based perovskite-type oxides as descriptors for chemocatalytic reactions

Perovskite-type transition metal (TM) oxides are effective catalysts in oxidation and decomposition reactions. Yet, the effect of compositional variation on catalytic efficacy is not well understood. The present analysis of electronic characteristics of B-site substituted LaCoO3 derivatives via in situ X-ray absorption spectroscopy (XAS) establishes correlations of electronic parameters with reaction rates: TM t2g and eg orbital occupancy yield volcano-type or non-linear correlations with NO oxidation, CO oxidation and N2O decomposition rates. Covalent O 2p-TM 3d interaction, in ultra-high vacuum, is a linear descriptor for reaction rates in NO oxidation and CO oxidation, and for N2O decomposition rates in O2 presence. Covalency crucially determines the ability of the catalytically active sites to interact with surface species during the kinetically relevant step of the reaction. The nature of the kinetically relevant step and of surface species involved lead to the vast effect of XAS measurement conditions on the validity of correlations.

Simultaneous desulfurization and denitrification from flue gas by catalytic ozonation combined with NH3/(NH4)2S2O8 absorption: Mechanisms and recovery of compound fertilizer

An integrated method of simultaneous desulfurization and denitrification from flue gas by catalytic ozonation combined with NH3/(NH4)2S2O8 absorption was developed for the first time. It consisted of two parts: (1) the catalytic ozonation of NO over FeOx/SAPO-34 to study the effects of the various influencing factors, and (2) the absorption–oxidation of NOx and SO2 induced by ozone combined with a NH3/(NH4)2S2O8 solution in a bubble column reactor. In Part 1, results showed that under the optimal condition of a molar ratio of 0.5 for O3/NO, a residence time of 3 s, a water vapor volume fraction of 4%, a NO initial concentration of 536 mg/m3, and a SO2 initial concentration of 343 mg/m3, the oxidation rate of NO was 55%. The characterizations of poisoned catalyst are briefly discussed. In Part 2, as the gas passed sequentially through the ozonizing reactor and the absorber (NH3/(NH4)2S2O8 solution of 0.8% ammonia and 0.2 mol/L (NH4)2S2O8), a NO conversion rate of approximately 92.6% and SO2 conversion rate of 100% were obtained. The pH of the NH3/(NH4)2S2O8 solution had a significant impact on the NO conversion. According to the analysis of the composition of products under different pHs, a mechanism of desulfurization and denitrification based on NH3/(NH4)2S2O8 solutions was proposed. The reaction product as a compound fertilizer contained up to 24.5% nitrogen.

Quantum Chemical Study on the Reaction Mechanism of NO Removal by Urea Combined with Hydrogen Peroxide

Using urea-H2O2 solution to remove NO by scrubbing is regarded as a relatively low-cost and promising denitrification method. For a good understanding and further improvement, the mechanism investigation on the NO removal by urea combined with H2O2 is essential. The denitrification mechanism is calculated and studied in detail by Quantum Chemistry in this paper. Results show that the most possible denitrification route is that oxidizing NO by H2O2 to produce HNO2 and then absorbing HNO2 by urea to produce N2, CO2 and H2O. The activation energy of NO oxidation by H2O2 (71.12 kJ/mol) is higher than that of HNO2 absorption by urea (60.17 kJ/mol). This indicates reaction H2O2 + 2NO → 2HNO2 is the rate-determining step and more difficult to carry out. The constraints of the NO removal are coming from NO oxidation rather than absorption in solution. Improving NO oxidation rate is the key to denitrification. The theoretical results in this paper provide theoretical basis and data reference for subsequent technological development.

Catalytic performance and reaction mechanism of NO oxidation over Co3O4 catalysts

Co3O4 nanorods and nanoparticles were prepared and differed in the overall particle sizes and shapes, while in both cases the catalytically active (110) lattice plane was mainly exposed. The forward rate of NO oxidation of Co3O4 nanorods, stated on catalyst weight, was higher than that of Co3O4 nanoparticles. However, the turnover frequency (TOF) numbers normalized by the surface Co3+ were almost the same, indicating that NO oxidation took place over the same active sites of surface Co3+ for both catalysts. Co3O4 nanorods had a larger number of exposed active sites than nanoparticles. The dissociation of surface O2*, formed by the quasi-equilibrated reaction of O2 molecules on vacant sites (*), assisted by gaseous NO to form NO2 and surface O*, was the rate-determining step in NO oxidation. In situ FTIR spectra confirmed that abundant bridged nitrates were formed on both Co3O4 nanorods and nanoparticles.

Global kinetic model of NO oxidation on Pd/γ-Al2O3 catalyst including PdO[formula omitted] formation and reduction by CO and C[formula omitted]H[formula omitted

Pd is often used in diesel oxidation catalysts (DOC) together with Pt to ensure thermal stability and durability. Besides CO and hydrocarbon oxidation, NO oxidation is important for the function of subsequent converters in the exhaust line, such as SCR and DPF. Though Pt sites exhibit a significantly higher NO oxidation rate, Pd also provide some catalytic activity for this reaction and therefore affect the overall NO2 yield in DOC. Palladium oxides (PdOx) formation decreases the NO oxidation activity like PtOx.We present a global kinetic model for Pd/γ-Al2O3 catalyst considering standard DOC reactions extended with the PdOx formation and its influence on the NO2 yield. The dynamics of transition between the metallic Pd and oxidized PdOx state is studied in repeated temperature ramps and isothermal deactivation experiments, revealing the individual impact of O2 and NO2. The model describes well a dual NO oxidation light-off behavior observed in the experiments.

Promotional effect of Ce doping in Cu4Al1Ox – LDO catalyst for low-T practical NH3-SCR: Steady-state and transient kinetics studies

There are very few catalysts reported so far to withstand poisoning by the co-presence of SO2, HCl and H2O in the flue gas stream for the NH3-SCR. The purpose of this work was to report for the first time, to the best of our knowledge, the development of a new catalyst, Ce2/Cu4Al1Ox-layered double oxide (LDO) with high low-temperature de-NOx activity and high poisoning resistance in the presence of H2O, HCl and SO2 in the feed gas stream. In particular, Ce2/Cu4Al1Ox-LDO catalyst in the presence of 5% H2O, 100 ppm HCl and 100 ppm SO2 in the NH3-SCR feed gas stream presented after 9 h of continuous reaction at 200 °C a relatively stable NOx conversion (ca. 57.2%), where all other three control catalysts tested, namely: Cu/Al2O3, Cu-Ce/Al2O3 and Cu4Al1Ox showed severe deactivation, where NOx conversion values of ∼0, 0 and 5.7%, respectively, were measured. It should be noted that the Ce2/Cu4Al1Ox catalyst achieved NOx conversion of 95.3% at 200 °C in the absence of HCl and SO2 in the feed gas stream. A suit of experimental techniques such as BET, XPS, ICS, in situ DRIFTS, pyridine- and NH3-FTIR, NH3-TPD, H2-TPR and transient NH3 chemisorption and NH3-SCR kinetics were employed to reveal possible reasons for the high activity and poisoning resistance exhibited by the Ce2/Cu4Al1Ox catalytic system. XRD and XPS analyses showed that Ce2/Cu4Al1Ox had highly dispersed Cu2+ and Ce3+ species, which likely promote the rate of NH3-SCR. Py-FTIR, NH3-TPD and H2-TPR results indicated that Ce2/Cu4Al1Ox has a larger concentration of surface acid sites and stronger redox properties. According to H2-TPR, ICS and in-situ DRIFTS analyses, the redox properties of Ce2/Cu4Al1Ox were significantly less affected by the presence of HCl and SO2 gases, and lower amounts of metal sulfate and metal chloride species were formed, thus proving its exhibited poisoning resistance. Transient kinetics experiments revealed that the larger site reactivity (k, s−1) and NO oxidation rate to NO2 and not the surface coverage of adsorbed NHx-s active intermediates dictates the higher rate of NH3-SCR over Ce2/Cu4Al1Ox compared to Cu/Al2O3 and Cu-Ce/Al2O3 non LDO- materials.

Strontium doping and impregnation onto alumina improve the NOx storage and reduction capacity of LaCoO3 perovskites

Here we report the effects of strontium doping of perovskites (La1-xSrxCoO3) on NOx storage and reduction (NSR) as well as the effects of supporting the perovskite onto an alumina support. The NSR capacity of La0.7Sr0.3CoO3 improved with strontium doping: this material displayed a good balance between NO oxidation capacity and adsorption sites accessibility. Increased accessibility was mainly due to the strontium oxide segregates. In addition, different loadings of La0.7Sr0.3CoO3 perovskite (10, 20, 30, 40 and 50%) were impregnated onto alumina in order to increase the exposed surface area of the perovskite. This had the effect of increasing the NSR capacity of the perovskite. The results of X-Ray diffraction, UV–vis–NIR spectroscopy, N2 adsorption-desorption, electron microscopy, and temperature programmed techniques, demonstrated that the cobalt ions preferably formed cobalt aluminate (CoAl2O4) in the case of low perovskite loadings (<20%). Meanwhile, a well-developed perovskite phase was observed with the higher loadings (>30%). The specific NO oxidation rate per gram of perovskite increased dramatically with the incorporation onto an alumina support. 30% LSCO/Al2O3 sample had an oxidation rate of 138 μmol min-1 (g LSCO)-1 at 350 °C, more than double the rate of the bulk La0.7Sr0.3CoO3 (49 μmol min−1 (g LSCO)−1). Likewise, the 30% LSCO/Al2O3 sample had a higher NOx storage capacity than its bulk counterpart at 400 °C: 306 vs. 115 μmol (g LSCO)−1. The higher oxidation capacity of the alumina-supported samples also facilitated the diffusion of the intermediate compounds from oxidation to adsorption sites. Impregnating alumina with perovskite could be used to improve the efficiency of perovskite mediated NOx removal in automobile applications. Furthermore, adding palladium onto optimum alumina-supported perovskite sample, i.e. 1.5% Pd-30% LSCO/Al2O3, resulted in a clear improvement in NOx storage and reduction capacity. This last sample demonstrated a nitrogen yield as high as 65%, an improvement over the model Pt-based NSR catalyst.

Structure–Activity Relationship Study of Mn/Fe Ratio Effects on Mn−Fe−Ce−Ox/γ-Al2O3 Nanocatalyst for NO Oxidation and Fast SCR Reaction

A series of Mn−Fe−Ce−Ox/γ-Al2O3 nanocatalysts were synthesized with different Mn/Fe ratios for the catalytic oxidation of NO into NO2 and the catalytic elimination of NOx via fast selective catalytic reduction (SCR) reaction. The effects of Mn/Fe ratio on the physicochemical properties of the samples were analyzed by means of various techniques including N2 adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H2-temperature-programmed reduction (TPR), NH3-temperature-programmed desorption (TPD) and NO-TPD, meanwhile, their catalytic performance was also evaluated and compared. Multiple characterizations revealed that the catalytic performance was highly dependent on the phase composition. The Mn15Fe15−Ce/Al sample with the Mn/Fe molar ratio of 1.0 presented the optimal structure characteristic among all tested samples, with the largest surface area, increased active components distributions, the reduced crystallinity and diminished particle sizes. In the meantime, the ratios of Mn4+/Mnn+, Fe2+/Fen+ and Ce3+/Cen+ in Mn15Fe15−Ce/Al samples were improved, which could enhance the redox capacity and increase the quantity of chemisorbed oxygen and oxygen vacancy, thus facilitating NO oxidation into NO2 and eventually promoting the fast SCR reaction. In accord with the structure results, the Mn15Fe15−Ce/Al sample exhibited the highest NO oxidation rate of 64.2% at 350 °C and the broadest temperature window of 75–350 °C with the NOx conversion &gt;90%. Based on the structure–activity relationship discussion, the catalytic mechanism over the Mn−Fe−Ce ternary components supported by γ-Al2O3 were proposed. Overall, it was believed that the optimization of Mn/Fe ratio in Mn−Fe−Ce/Al nanocatalyst was an extremely effective method to improve the structure–activity relationships for NO pre-oxidation and the fast SCR reaction.