Catalyst For NO Oxidation Research Articles

The promotion of rare earth on Pt-SiO2-Al2O3 catalyst for NO oxidation in diesel exhaust

The effective oxidation of NO is the key to the catalytic treatment of diesel vehicle exhaust. Improving the NO oxidation ability is mainly to optimize the chemical state of the active site (Pt), followed by increasing the number of active centers. Considering that the atoms with electronegativity weaker than Pt can provide electrons to change the chemical state of Pt, rare earth elements with weak electronegativity are selected as additives to obtain Pt/M-SiO2-Al2O3 (M = Sc, Y, La, Ce, Pr, Nd, Sm, Eu) catalysts by co-impregnation method. Among them, the Pt/La-SiO2-Al2O3 catalyst has the best NO oxidation performance, compared with the Pt-SiO2-Al2O3, the NO conversion rate increased by 28 %. Due to the special outer electron arrangement of La, its electronegativity is the smallest in rare earth, which makes its outer electrons easy to transfer to Pt atoms, and has the strongest electron interaction. Thus, the highest content of Pt0 was detected in CO diffuse reflectance infrared Fourier transform spectroscopy (CO-DRIFTS) and X-ray photoelectron spectroscopy (XPS). In addition, CO chemisorption and transmission electron microscopy (TEM) confirmed that the introduction of La in the catalyst can significantly improve the dispersion of precious metals. Notably, this simple approach of affecting electron interaction by introducing weakly electronegative elements provides a reference for the design of noble metal catalysts with different valence states to solve complex problems.

An effective cascade strategy over a Sn-enriched phosphate material: Upcycling a reductive adsorbent into an environmental catalyst

A calcium phosphate-based material enriched with Sn (8.3 at.%, as revealed by X-ray photoelectron spectroscopy) was successfully used in the reductive adsorption of Cr(VI) to Cr(III) for water remediation and, after use, repurposed into a catalyst for NO oxidation into NO2.The use of multiple characterization techniques (Mӧssbauer spectroscopy, synchrotron X-ray diffraction, TEM, and HAADF-STEM/EDS) provided information on Sn-speciation (Sn(II)/Sn(IV) = 1.2), structural composition, and morphological features. Cassiterite (rutile-type SnO2) and hydroromarchite (tin oxide-hydroxide Sn6O4(OH)4) crystalline phases characterized the material, along with the presence of an amorphous Ca3(PO4)2 phase.Notably, about 15 mgCr(VI)∙g−1 could be effectively reduced over a broad pH range (2–11), even in the simultaneous presence of various anions and cations, with concurrent adsorption of the resulting Cr(III), thanks to the adsorption properties of the phosphate phase. The kinetic constant of Cr(VI) removal was as high as 0.0058 g∙mg−1∙min−1 and increased in the presence of a pool of cations (0.0147 g∙mg−1∙min−1). The catalytic performances of the adsorbent after use in Cr(VI) reductive adsorption were studied in the 150–450 °C interval at 15,000–80,000 h−1 space velocity. About 90 % of NO conversion at 350 °C was observed.This study highlights the adaptability and efficiency of the developed material across different environmental remediation processes.

Nickel-cobalt-based catalysts for CO and NO oxidation; their activation

Nickel-cobalt-based catalysts for CO and NO oxidation; their activation

Highly Efficient Ce and Co Codoped OMS-2 Catalyst for NO Oxidation

Highly Efficient Ce and Co Codoped OMS-2 Catalyst for NO Oxidation

Highly disordered MnOx catalyst for NO oxidation at medium–low temperatures

Recently, the selective catalytic oxidation of NO (NO-SCO) has garnered significant surge of interest because of its pivotal role in many deNOx techniques. Particularly, NO-SCO at moderate to low temperatures ranging from 100 °C to 200 °C has garnered increasing attention, as in certain industries such as steel, cement and glass, the flue gas temperature typically falls within the range of 100 °C to 200 °C. Manganese oxides (MnOx) have emerged as promising NO-SCO catalysts, mainly due to their notable activity in NO-SCO, affordability, and environmental friendliness. However, their NO-SCO performance at medium–low temperatures of 100–200 °C is unsatisfactory. Given that introducing oxygen vacancies (OVs) into MnOx to increase the concentration of surface chemisorbed oxygen (Oads) could be a potential approach to enhance its NO-SCO performance, herein, two disordered MnOx catalysts enriched with abundant OVs were synthesized via simple thermal decomposition of manganese oxalate (MnOx-O) and manganese carbonate (MnOx-C) in air. Characterization results demonstrate that both MnOx-O and MnOx-C catalysts exhibited higher NO-SCO performance than the benchmark γ-MnO2 catalyst within the temperature range of 100–200 °C, and the disordered structure and the associated beneficial properties of MnOx-O and MnOx-C were believed to contribute to their excellent NO-SCO performance. This study provides a novel approach for synthesizing MnOx catalysts with high NO-SCO performance at medium–low temperatures of 100–200 °C.

Three-dimensional ordered macroporous LaFe1-xMnxO3 with high stability for efficient NO oxidation and sulfur resistance.

NOx is an air pollutant that affects human health. A series of perovskite catalysts with different ratios of lanthanum, iron, and manganese and a three-dimensional ordered microporous structure was prepared, and the strongest catalytic performance was obtained with the LaFe0.1Mn0.9O3 catalyst. LaFe0.1Mn0.9O3 possesses the greatest number of oxygen vacancies and reached 77% NO oxidation conversion at 250 °C, with the highest NO oxidation conversion of 99% at 318 °C. This work provides a promising non-precious metal catalyst for NO oxidation and soot combustion.

Alkali metal enhanced cerium manganese-based three-dimensional ordered macroporous catalyst for NO oxidation and soot combustion

Alkali metal can control the redox potential of the reaction system, modify the surface electronic structure, improve the stability of catalyst. Herein, we dop the alkali metal into cerium manganese-based...

Positive effects of the Sr doping on LaCoO3 perovskites for simultaneous catalytic oxidation performances of NO and Hg0

LaCoO3 perovskite, with a general formula of ABO3, have received significant attention as environmental functional catalysts for NO and Hg0 oxidation owing to their compositional adjustability and chemical stability. Structural modifications of the perovskite have been performed through the substitution of La atoms at the A-site with atoms of different ion radii to enhance the oxidation ability. In this study, herein, a series of La1–xSrxCoO3 (x = 0.1–0.5) perovskites were synthesized, resulting in a transition from the R–3C rhombohedral phase structure to the Pm-3m cubic phase. Sr doping was effective in improving the oxidation of NO and Hg0. The improved catalytic activity was attributable to the generation of more electronegative Co3+ and the higher content of surface-adsorbed oxygen species. Moreover, Sr doping enhanced the redox performance and reduced the reaction temperature. Notably, SrCO3 species were the main factors responsible for the reducing the activation of La1–xSrxCoO3 (x = 0.1–0.5) perovskites, which could be detected when the Sr doping content exceeded 0.4. This study provides a screening strategic idea for the designing highly active perovskite catalysts.

Theoretical study on NO oxidation using single metal atom catalysis embedded graphene with N4 vacancy

This work investigates the potential NO oxidation schemes using a graphene with N4 vacancy (GrN4) monolayer doped with transition metals (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) for single-atom catalysis (SAC). The GrN4 monolayer is proven capable of greatly suppressing the clustering tendency of TM atoms due to its strong binding ability. Moreover, the Ti-GrN4 systems exhibit considerable affinity towards both NO and O2, meeting a fundamental criterion for kick-starting the catalytic cycle. Three dissimilar mechanisms: Eley-Rideal (ER), Langmuir-Hinshelwood (LH), and trimolecular Eley-Rideal (TER) mechanisms were examined for the NO oxidation in Ti-GrN4 SAC. The calculated activation barriers indicate that the LH pathway is the preferred mechanism, in which the NO + O2 reaction can form the OONO intermediate, then generate and release NO2 molecules. Therefore, Ti-supported GrN4 has the potential to be a strong single-atom catalyst for NO oxidation at low temperatures.

Redox transformations of Ru catalyst during NO oxidation at industrial nitric acid production conditions

Oxidation of nitric oxide is one of the main steps in the Ostwald process for industrial nitric acid production. This work summarises the use of γ-Al2O3 supported Ru catalyst to study the oxidation of NO to NO2 at ambient and 4 bar pressure with a feed of 10% NO, 6% O2, 15% H2O, and rest Ar. The catalyst was synthesised using wet impregnation and characterised by BET, CO chemisorption, H2-TPR, XPS, XRD, in-situ XAS-XRD and DRIFTS. We report the activity and kinetics of supported ruthenium catalyst for NO oxidation under realistic nitric acid plant conditions. The catalyst exhibited a promising low-temperature activity of 72% at 340 °C in complete nitric acid condition and 37% at 420 °C in partial nitric acid condition. An apparent activation energy of 152 kJ/mol was observed and the overall rate was determined to be r =kf.KG.PNO2.PO2PNO2, where kf and KG represents forward rate and equilibrium rate constants respectively. The reaction was found to be second order with respect to NO, first order with respect to O2 and inversely dependent on NO2 partial pressure. The stability of the catalyst was also tested during 45 h of isothermal NO oxidation at ambient pressure. From in-situ XAS-XRD and DRIFTS experiments it was revealed that during isothermal NO oxidation the reaction oscillates as the ruthenium surface goes through redox cycles. A plausible reaction mechanism that fits with our experimental observations and the oxidative nature of ruthenium is proposed. This study demonstrates and explains the capacity of supported ruthenium catalysts to oxidise NO to NO2 in industrial nitric acid production conditions.

Insight into the difference in the adsorption behavior of NO/SO2/H2O by cobalt oxide

NO pollutants are one of the key environmental hazards. Co3O4 has been identified as a high-performance catalyst for NO oxidation. However, the adsorption behavior of NO/SO2/H2O co-existing gas has not been well understood. This computational work examined the difference in the adsorption behavior of NO/SO2/H2O over Co-site based on a combined study using molecular orbital analysis, crystal field theory, and density functional theory calculations. It is demonstrated that NO adsorption over Co-site is relatively weak concerning SO2 and H2O due to weak electron transfer·H2O adsorption is particularly strong due to interface bonding and hydrogen bonding.

Constructing γ-MnO2 with abundant oxygen vacancies by a chelating agent-assistant strategy to achieve high-efficient conversion of NO to NO2

To date, the exploitation of non-noble materials of high-efficiency and low-temperature conversion of NO to NO2 still existed as a challenging task due to high cost of current Pt-based commercial catalysts. Herein, we employed a chelating agent-assistant strategy to regulate the content of oxygen vacancy over γ-MnO2 catalysts, which were further used for NO oxidation. Benefiting from the structure-directing effect of tartaric acid, the resultant locus-shaped γ-MnO2 catalyst with abundant oxygen vacancies showed a remarkable low-temperature catalytic activity (T50 and T92 of 127 and 225 °C; respectively), which was superior to unmodified γ-MnO2 sample (T50 at 189 °C) and those recently reported good-performing NO oxidation catalysts. An array of characterization results revealed that an extended capping by means of chelating agents could effectively weaken the MnO bond strength and promote the formation of oxygen vacancy (OVs), thus tremendously increase the amount of surface-active oxygen species. Moreover, theoretical calculation demonstrated that an enriched OVs concentration could enhance the reactivity of surface lattice oxygen by reducing the formation energy of OVs, further accelerating reaction rate of the adsorption/activation of O2 molecules and thus bringing about an outstanding low-temperature catalytic activity. This study highlighted the potential of chelating agents in the design of high-efficient catalysts for environmental remediation and beyond.

Core-shell MnCeO catalysts for NO oxidation and mild temperature diesel soot combustion

Environmental contamination such as soot particles and NO x have aroused extensive attraction recently. However, the main challenge lies in the oxidation of soot at mild temperature with the assistance of NO x . Here, a series of core–shell MnCeO x catalysts were successfully synthesized by hydrothermal method and employed for low-temperature catalytic oxidation of soot in the presence of NO x . X-ray diffraction (XRD), inductively coupled plasma - optical emission spectrometry (ICP-OES), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), N 2 adsorption/desorption, H 2 -temperature programmed reduction (H 2 -TPR), O 2 -temperature programmed desorption (O 2 -TPD), X-ray photoelectron spectroscopy (XPS) and Raman were conducted for identifying the structure of prepared catalysts and investigating redox properties of the core–shell mixed oxide, which shows excellent performance for NO oxidation and the T 50 about 350 °C for soot oxidation. Besides, soot particle is oxided at 304 °C in presence of NO, while T 50 augments up to 340 °C in the absence of NO. In the NO x -assisted elimination cases of soot, NO 2 generated from NO in emission gas is generally reckoned as a facilitator which significantly reduces ignition temperature of soot particles. Possible catalytic mechanism over core–shell MnCeO x catalysts is also proposed in this paper. Core-shell MnCeO x catalysts with different Mn contents were successfully synthesized through hydrothermal method and they exhibit superior catalytic ability for soot oxidation. This work achieves NO x -assisted soot combustion at mild temperature and can be used as alternative option in catalytic processes of soot particles. • A series of MnCeO x catalysts were successfully synthesized by hydrothermal method and the core-shell structure is confirmed. • MnCeO x catalysts showed superior catalytic capability for low-temperature catalytic oxidation of soot in the presence of NO x and the lowest catalytic temperature was achieved at 304 °C. • Possible catalytic mechanism over core-shell MnCeO x catalysts was also proposed.

Understanding structure-performance relationships of CoOx/CeO2 catalysts for NO catalytic oxidation: Facet tailoring and bimetallic interface designing

Crystalline structure and bimetallic interaction of metal oxides are essential factors to determine the catalytic activity. Herein, three different CoOx/CeO2 catalysts, employing CeO2 nanorods (predominately exposed {110 facet), CeO2 nanopolyhedra ({111} facet) and CeO2 nanocubes ({100} facet) as the supports, are successfully prepared for investigating the effect of exposed crystal facets and bimetallic interface interaction on NO oxidation. In comparison with the {111} and {100} facets, the exposed crystal facet {110} exists the best superiority to anchor and stabilize Co species. Moreover, ultra-small CoOx clusters composed of strong Co-O coordination shells with minor Co-O-Ce interaction are formed and uniformly dispersed on the CeO2 nanorods. Structural characterizations reveal that the active exposed crystal facet {110} and the strong bimetallic interface interaction in CoOx/CeO2-nanorods (R-CC) result in more structural defect, endowing it with abundant oxygen vacancies, excellent reducibility and strong adsorption capacity. The DRIFTs spectra further indicate that the exposed crystal facet {110} has a significant promoting effect on the strength of nitrates compared with {111} and {100} facets. The bimetallic interface interaction not only significantly facilitates the formation of nitrate species at lower temperature, but also effectively suppresses the generation of sulfate and lower the sulphation rate. Therefore, R-CC catalyst exhibits the maximum NO oxidation activity with the conversion of 86.4 % at 300 °C and still sustains its high activity under cyclic condition or 50 ppm SO2. The provided crystalline structure and interaction-enhanced strategy sheds light on the design of high-activity NO oxidation catalysts.

Design of single-atom catalysts for NO oxidation using OH radicals

Volcano plot of NO oxidation using OH and O2 over TM-N4-C.

Experimental study on supported MnO2-based catalysts for NO oxidation

Experimental study on supported MnO2-based catalysts for NO oxidation

Co-Precipitated Mn0.15Ce0.85O2−δ Catalysts for NO Oxidation: Manganese Precursors and Mn-Ce Interactions

Two Mn0.15Ce0.85O2−δ mixed oxides were synthesized by a co-precipitation method using Mn(NO3)2 and KMnO4 as the manganese precursors, respectively. Structural analyses by X-ray powder diffraction and Raman spectroscopy reveal the formation of MnOx-CeO2 solid solutions. The Mn0.15Ce0.85O2−δ catalyst prepared from the high-valent manganese precursor exhibits higher activity for the catalytic oxidation of NO. The advantage of KMnO4 is related to the improved redox property of the catalyst as supported by H2 temperature-programmed reduction (TPR) and O2 temperature-programmed desorption (TPD). The Mn-Ce interactions create more Mn4+, Ce3+ and oxygen vacancies on the KMnO4-synthesized mixed oxides based on the Raman and X-ray photoelectron spectra (XPS).

Nitrogen atom coordination tuned transition metal catalysts for NO oxidation and reduction

Developing an efficient catalyst for NO oxidation and reduction at ambient temperature is a significant challenge. Recent studies have suggested that the N-coordinated transition metal (TM) single atom catalysts (SACs) have high catalytic activity and stability. Herein, we report the activation potential of a series of 3d TM atoms supported on N coordination-tuned graphene (GR) for NO oxidation and reduction. The results show that the N coordination pattern can greatly alter the catalytic reactivity of TM on the catalysts, and the TM atom on the catalysts with three-coordinated pyridinic nitrogen TM-N3@GR exhibit the strongest chemical activity. Among the TM-N3@GR catalysts, Ti–N3@GR is the most promising candidate. The rate constants and equilibrium constants were calculated to evaluate the kinetic and thermodynamic feasibility of the catalytic reaction, respectively. Our results demonstrate that the reduction of NO to N2 on Ti–N3@GR can occur at ambient temperature with a large exotherm of 6.99 eV, and the oxidation of NO to NO2 on Ti–N3@GR can easily proceed when the temperature reaches 360 K with a large equilibrium constant. Our studies are of great significance for understanding the performance of N coordination-tuned catalysts and designing Ti-based catalysts for NO oxidation and reduction.

Facile synthesis of Schistose-like Co-Mn oxides for low-temperature catalytic oxidation of NO with enhanced SO2/H2O tolerance

The schistose-like Mn-Co oxides were synthesized by thermal decomposition of inorganic salts as catalyst for NO oxidation. The morphological and surface structural properties can be efficiently regulated by controlling the ratio of Co/Mn. Schistose-layered structure with plentiful nanopores not only facilitates the exposure of active sites but also improves the diffusion and adsorption of NO. Abundant active oxygen species and highly content of Mn4+ formed on the surface of Co1Mn4 play a vital role in the catalytic oxidation of NO. Thus, Co1Mn4 catalyst achieves the highest conversion rate of 54.4 % at 120 °C and 91.3 % at 240 °C. Moreover, satisfactory long-time stability as well as outstanding tolerance to SO2 and H2O could be obtained for Co1Mn4 catalyst. Distinct distinctions on the variation of nitrate/nitrite species over Mn and Co1Mn4 are discovered by in-situ DRIFTS, which provided basis for elucidating the reaction mechanism. This work broadens the horizons for the design of bimetallic catalysts for low-temperature NO oxidation.

A first-principles based microkinetic study of ZnMn1.5TM0.5O4 (TM = 3d transition metal) for NO oxidation

A highly-efficient NO oxidation catalyst is urgently needed due to serious NO pollution. Herein, we perform first principles calculations and microkinetic analysis to investigate NO oxidation properties of pristine and 3d transition metal doped ZnMn2O4 that exhibits similar Mn-Mn dimer features to SmMn2O5. It is found that two different categories of NO oxidation mechanism with different O2 adsorption and dissociation behaviors occur on pristine and B-site doped ZnMn2O4. The microkinetic analysis shows that Cu, Fe, Zn, Ti, Cr and Ni doping can effectively promote the reaction rates of NO oxidation, with Cu and Fe doped ZnMn2O4 showing the best low-temperature NO oxidation performance. Sc, V, and Co doping are predicted not to be beneficial to performance enhancement. A general relation between NO oxidation reactivity and NO adsorption energies is proposed to quantitatively depict the key factors influencing NO oxidation performance. The relation provides a specific strategy for the optimization of NO oxidation that ZnMn1.5TM0.5O4 (TM = 3d transition metal) with first and second NO adsorption energies (Ead) in the ranges of −2.40 ∼ −2.00 eV and −1.50 ∼ −0.25 eV respectively have good NO oxidation performance, respectively. Our paper paves a feasible road for the applications of ZnMn1.5TM0.5O4 as the NO oxidation catalyst.