Activity For Soot Combustion Research Articles

Real biofuel and fossil-fuel soot combustion activities in active and passive regeneration of diesel/gasoline particulate filters under different O2/NOx concentrations.

In this work, we aim to investigate and compare the combustion reactivities of real biofuel soot and fossil-fuel soot in the active and passive regeneration conditions of DPF and GPF through temperature-programmed oxidation (TPO). Higher reactivity of biofuel soot is achieved even under GPF conditions with extremely low oxygen concentration (~ 1%), which provides a great potential for low-temperature regeneration of GPF. Such a result is mainly attributed to the low graphitization and less surface C = C groups of biofuel soot. Unfortunately, the presence of high-content ashes (~ 47%) and P impurity in real biofuel soot hinder its combustion reactivity. TPO evidences that the O2/NOX-lacking conditions in GPF are key factors to impact the combustion of soot, especially fossil-fuel soot. This work provides some useful information for understanding real biofuel and fossil-fuel soot combustion in GPF and DPF regeneration and further improvement in filter regeneration process.

Co,Ce nanoparticles supported on stacked wire mesh cartridges. Activity and stability in diesel soot combustion

In this work, Co3O4 nanoparticles were successfully synthesized by precipitating a precursor salt solution in the form of microdroplets generated by a nebulizer, as an efficient, fast and low-cost approach. After drying and calcination, synthesized particles were deposited on stacked wire mesh monoliths by immersing the structures in a suspension containing synthesized Co3O4 particles and commercial ceria nanoparticles as a binder. These structured catalysts were evaluated for the combustion of diesel soot which constitutes a crucial step in the regeneration of catalytic particulate filters (CDPFs). Thermal and mechanical stability of Co,Ce washcoated monoliths were investigated. For this, successive catalytic evaluations of the structured system, with intermediate treatments at 900 °C (accelerated aging), were carried out indicating a very good activity and stability of the catalysts developed. Adherence tests showed good adhesion of the catalytic layer to the metallic substrate. Fresh and aged catalysts were fully characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Laser Raman Spectroscopy (LRS) and Temperature-Programmed Reduction (TPR). It was found that the catalytic coating resulted composed of nanometric CeO2 and Co3O4 along with chromium, iron and manganese oxides coming from the migration of the metallic substrate, in the catalytic cartridge calcined at 600 °C. Despite after calcination at 900 °C spinels of Co, Fe, Cr and Mn were observed, these oxides did not significantly affected the catalytic activity. Although this aging treatment at 900 °C was severe and is not expected under real conditions, it highlights the potential application of the catalytic metallic cartridges here developed.

Magnesium borate whiskers/La2-XCeXZr2O7 catalysts preparation on cordierite honeycomb ceramic surfaces for soot catalytic oxidation͏

Magnesium borate whiskers were used to prepare a hierarchical microstructure on cordierite ceramic substrate through the precipitation-molten salt method. The La2-XCeXZr2O7 catalyst was then loaded onto the magnesium borate whiskers to form the hierarchical microstructure. The Ce-doped catalysts exhibited a significant improvement in the catalytic activity of soot combustion compared to the La2Zr2O7 catalyst. The study employed various techniques to characterize the structural morphology and phase composition, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform-infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The growth of Magnesium borate whiskers (Mg2B2O5) with diameters of 100–200 nm and lengths of 2–5 μm were grown and tightly bonded to the cordierite ceramic substrate to mimic the structure of human respiratory system cilia. This could improve the filtration efficiency of soot in car exhaust. BET analysis showed that the specific surface area of cordierite increased from 0.684 m2/g to 1.363 m2/g after whisker growth. The study confirmed that the whiskers were firmly attached to the cordierite ceramic substrate, as demonstrated by the binding strength experiments. The addition of Ce metal has been found to significantly enhance soot combustion due to the presence of more active oxygen species and superior mobility of lattice oxygen species with more oxygen vacancies. The catalyst's intrinsic redox property was characterized using X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR). The semi-quantitative thermogravimetric analysis (TG-DTG) and the temperature-programmed oxidation (TPO) of catalysts showed that Z-La1.9Ce0·1Zr2O7 exhibited the highest catalytic activity for soot combustion, with an ignition temperature of 268 °C, a peak temperature of 418 °C, and a temperature of 90 % soot conversion of 464 °C. Furthermore, cyclic stability experiments demonstrate that the Z-La1.9Ce0·1Zr2O7 catalyst exhibits excellent structural stability and consistent catalytic performance. This distinctive microstructure holds great potential for applications in the field of DPF.

Decoding the Reactivity Enhancement of Ln2Ce2O7 Compounds (Ln = Yb, Y, Tb, and Gd) for Soot Combustion: The Remarkable Contribution of Variable Valence A-Sites.

The impact of variable valence A-sites on the redox property and reactivity of Ln2Ce2O7 compounds in soot particulate combustion has been investigated. It was observed that Yb2Ce2O7, Y2Ce2O7, and Gd2Ce2O7 formed a rare earth C-type phase, while Tb2Ce2O7 formed a solid solution phase. Both Tb2Ce2O7 and Yb2Ce2O7 possess dual valence state A-sites, resulting in significantly more surface vacancies. Additionally, the advantageous solid solution phase structure of Tb2Ce2O7 leads to even more surface vacancies than Yb2Ce2O7, which is crucial to generate active oxygen sites. Moreover, the introduction of NO into the reaction feed enhances combustion activity by producing active surface monodentate nitrates. A catalyst with higher numbers of surface vacancies exhibits improved NO oxidation ability and better NO2 utilization efficiency. Consequently, the Tb2Ce2O7 compound demonstrates not only the best soot combustion activity, but also an optimal NOx-assistance effect. Therefore, it is concluded that variable valence A-site is the intrinsic factor to improve the reactivity of Ln2Ce2O7 catalysts.

Studying the Structure‐Reactivity Relationship of CuO/CeO2 for Catalytic Soot Particulate Combustion: On the Monolayer Dispersion Threshold Effect

AbstractTo elucidate structure‐reactivity relationship and prepare improved catalysts for soot combustion, a series of CuO/CeO2 with different loadings have been fabricated by the impregnation method. With XRD and XPS extrapolation methods, it is disclosed that CuO disperses finely on the CeO2 support to form a monolayer with a capacity around 1.06 mmol 100 m−2, which equals to 2.9 wt. % CuO loading. Below this capacity, CuO is in a sub‐monolayer state. However, above this capacity, CuO micro‐crystallites are formed, and co‐exist with the monolayer CuO. By increasing CuO loading, soot combustion activity of the catalysts increases as well until it reaches the monolayer dispersion capacity. Further increasing the CuO loading to 5 % decreases the activity slightly, and then remains constant. Therefore, an apparent monolayer dispersion threshold effect is observed for soot combustion on CuO/CeO2 catalysts. It is found that the amount of surface‐active O2− sites plays critical role for the catalytic activity. To obtain the most active CuO/CeO2 catalyst, a monolayer amount of CuO should be loaded on the supports.

Potassium and cobalt double-doped ferrierites as a new class of soot oxidation catalysts

Research efforts to develop an effective soot oxidation catalyst have intensified in recent years due to the increased awareness of the highly harmful effect of soot particles on the human health and the environment. Large-scale application of a developed catalyst calls for a cheap support material allowing for an effective dispersion and thus a decrease in the active phase loading. Zeolites, widely used in catalysis as active phase carriers, possess advantageous characteristics such as a uniform porous structure and large surface area. Furthermore, they are characterized by high availability, good price, and are environmentally friendly. Cobalt-based materials provide promising soot oxidation catalyst phases, and alkali doping can further enhance their activity. This study focuses on the optimization of the potassium loading in the potassium and cobalt double-doped ferrierites towards a new class of cheap and environmentally friendly soot combustion catalysts. The potassium doping of the ferrierite-supported cobalt spienel was optimized in the range of 0–14 wt%. The obtained materials were characterized in terms of their composition (XRF, XPS, XRD, Raman spectroscopy), morphology (SEM, TEM/EDX/FFT), and reducibility (H2-TPR), and tested in the process of soot oxidation in tight and loose contact modes. The strong promotional effect of potassium was discussed in terms of a significant modification of the catalyst electronic properties (work function studies) and supported by the potassium surface state studies by the alkali thermal desorption method (SR-TAD). It was found that the optimal potassium promoter dispersion leads to the lowest catalyst work function and its highest activity in soot combustion. The effect of nitric oxide was also investigated for selected catalysts. The opposite effect of NO on the activity of undoped and K-doped catalysts was discussed on the basis of in-depth spectroscopic studies. An enhanced formation of nitrate species was found on the surface of the K-containing catalyst which led to the stronger inhibiting effect of NO.

Surface tuning of 3DOM LaFe0.6Mg0.4O3 perovskite by acid etching to enhance catalytic performance for soot combustion

Acid etching is one of the most widely used methods for surface tuning of perovskite. In this paper, 3DOM LaFe0.6Mg0.4O3 was synthesized by a colloidal crystal template method, and was further etched by acetic acid at different times, which made the Mg element at the B-site of perovskite selectively dissolved. Through analysis of multiple characterization results, the introduction of B-site deficiency by acid etching could not only enhance oxygen vacancies, form the Fe4+/Fe3+ redox cycles on the surface of the catalyst, but also generate mesopores structure and increase the specific surface area. After acid treatment, the soot and NO oxidation performances were improved. Among all the as-prepared catalysts, 3DOM LaFe0.6Mg0.4O3 treated by acetic acid for 1 h (LFM-1) exhibited superior reducibility and better activity for soot combustion. The T50 of LFM-1 was 417 °C under 5 % O2/N2 and 500 ppm NO, and the activation energy and TOF were 66 kJ·mol−1 and 2.17 × 10-3 s−1, respectively. Herein, the strategy of introducing B-site deficient by acid treatment is an effective method to improve soot combustion activity, which might be applicable to other catalytic fields.

An isotopic study on oxygen uptake/exchange over ceria-praseodymia mixed oxides with pulse experiments using 18O2: Implications on soot combustion activities in the GDI (Gasoline Direct Injection) context

This research work focuses on a preliminary study of the behaviour of several ceria-praseodymia mixed oxides along with three model catalysts under isotopic oxygen pulses at different temperatures in an attempt to investigate their ability to interact with 18O2 (uptaking/releasing/exchanging) with their own lattice oxygen, under conditions which could simulate those existing in GDI exhaust gases. Furthermore, these ceria-praseodymia mixed oxides were studied to explore their responses towards soot combustion under two consecutive 18O2 pulses at 500 °C. It was observed that the capacity of oxygen activation and uptake is very dependent on the nature of the catalyst. Ce1−xPrxO2-δ catalysts present different responses in the O2 activation and uptake processes, as a function of temperature, praseodymium content and method of preparation. Moreover, some of these ceria-praseodymia formulations exhibited high soot combustion activity with a marked intervention of unlabelled active oxygen species during the inert period after the 18O2 pulse.

In situ growth of ZnO nanorods on monolithic diesel particulate filters and supporting potassium for catalytic soot combustion

Soot particulate is one of the most important pollutants emitted from diesel engines. A monolithic wall-flow diesel particulate filter (DPF) is a commercial technology for the removal of soot via filtration and subsequent combustion with/without catalysts. Herein, in situ grown ZnO nanorods on DPFs are applied to improve both soot and potassium (K)-based catalyst dispersion efficiency and thus enhancing the activity of DPF regeneration. The pretreatment and hydrothermal synthesis procedures for the homogenously covered ZnO nanorod arrays were specifically investigated on aluminum titanate (Al2TiO5) and silicon carbide (SiC) and compared with cordierite (Mg2Al4Si5O18). Potassium carbonate (K2CO3) is further supported on these monolithic substrates with in situ grown ZnO nanorods acting as catalytic active components for soot combustion. The coexistence of in situ grown ZnO nanorods and K active species on the three monoliths leads to much better soot combustion activity than those bare monoliths. The ZnO nanorods can not only trap soot to improve the contact efficiency between soot and catalysts, but also disperse the active K species. This demonstrates a promising strategy to develop highly active catalytic DPF for diesel soot removal.

Synergistic Effect of Pt and Dual Ni/Co Cations in Hydrotalcite-Derived Pt/Ni1.5Co0.5AlO Catalysts for Promoting Soot Combustion

In this article, the catalysts of hydrotalcite-derived Ni1.5Co0.5AlO nanosheet-supported highly dispersed Pt nanoparticles (Ptn/Ni1.5Co0.5AlO, where n% is the weigh percentage of the Pt element in the catalysts) were elaborately fabricated by the gas-bubble-assisted membrane--reduction method. The specific porous structure formed by the stack of hydrotalcite-derived Ni1.5Co0.5AlO nanosheets can increase the transfer mass efficiency of the reactants (O2, NO, and soot) and the strong Pt-Ni1.5Co0.5AlO interaction can weaken the Ni/Co-O bond for promoting the mobility of lattice oxygen and the formation of surface-oxygen vacancies. The Ptn/Ni1.5Co0.5AlO catalysts exhibited excellent catalytic activity and stability during diesel soot combustion under the loose contact mode between soot particles and catalysts. Among all the catalysts, the Pt2/Ni1.5Co0.5AlO catalyst showed the highest catalytic activities for soot combustion (T50 = 350 °C, TOF = 6.63 × 10-3 s-1). Based on the characterization results, the catalytic mechanism for soot combustion is proposed: the synergistic effect of Pt and dual Ni/Co cations in the Pt/Ni1.5Co0.5AlO catalysts can promote the vital step of catalyzing NO oxidation to NO2 in the NO-assisted soot oxidation mechanism. This insight into the synergistic effect of Pt and dual Ni/Co cations for soot combustion provides new strategies for reducing the amounts of noble metals in high-efficient catalysts.

Effect of yttrium and manganese addition on catalytic soot combustion activity and anti-high-temperature stability of CeO2 catalyst

In order to analyze the influence of the addition of yttrium and manganese on the soot combustion performance and high temperature stability of CeO2 catalyst, a series of Y/Mn-modified CeO2 catalysts were prepared. The effects of structural properties, textural properties, oxygen vacancies, Ce3+, surface adsorbed oxygen species, reduction properties and desorption properties of oxygen species on the activity were analyzed by various characterization methods. The results of the activity test show that the addition of manganese is beneficial to enhancement of the activity, while the addition of yttrium increases the amount of reactive oxygen species, but decreases the activity. After aging at 700 °C, the activity of the CeMn catalyst decreases most sharply, while the catalytic activity of the CeY catalyst can be maintained to a certain extent. Interestingly, the addition of yttrium and manganese at the same time can stabilize the activity. The fundamental reason is that yttrium and manganese move to the surface of the solid solution after aging, which increases the reduction performance of the catalyst, thus contributing to the increase of activity. Although the activity of CeYMn catalyst decreases after aging at 800 °C, it is still higher than that of other catalysts aged at 700 °C.

The promoting effect of Pt loaded with different redox supports on NO[sbnd]NO2 cycle-assisted soot combustion

Supports with different redox properties (Al2O3, Ce0.5Zr0.5O2-Al2O3, Ce0.5Zr0.5O2) and their corresponding Pt-based catalysts were prepared to investigate the effect of the suitability between Pt and different supports and the promotion of the NONO2 cycle on the catalytic activity of soot combustion. It is interesting that Pt-loaded nonredox support Al2O3 exhibited a poor catalytic activity for soot combustion in the absence of NO but an excellent catalytic activity in the presence of NO. However, unlike the Al2O3 support, Pt loaded Ce0.5Zr0.5O2-Al2O3 and Ce0.5Zr0.5O2 as redox supports showed an opposite result. N2 adsorption-desorption and XRD results indicated that Pt loading had no obvious effect on the texture properties of the supports. More zero-valent Pt (Pt0) on Pt/Al2O3 revealed by XRD, CO chemisorption and XPS was suggested as a major factor for promoting NO oxidizing cycles. Therefore, an amount of NO2 molecules produced on Pt0 is key to accelerate soot combustion under loose contact. The weak interaction between Pt and Al2O3 kept more Pt in the lower valence state. The Pt from Pt/Ce0.5Zr0.5O2-Al2O3 and Pt/Ce0.5Zr0.5O2 reduced the number of NONO2 cycles and further limited the assistance of NO2 in soot combustion due to a high-valence state of most of Pt. However, the preferable reducibility of the redox supports benefit soot combustion in O2/N2 because of the presence of active oxygen. This work would provide a new understanding for the further improvement of soot oxidation with the catalysts.

Highly Efficient Catalysts of AuPd Alloy Nanoparticles Supported on 3D Ordered Macroporous Al2O3 for Soot Combustion

AbstractThe catalysts of Au−Pd bimetallic nanoparticles with different Au/Pd ratios supported on 3DOM Al2O3 were synthesized by micropores‐diffused reduction (MDR) method. Compared with supported monometallic Au or Pd catalysts, supported bimetallic Au−Pd nanoparticle catalysts, especially Au2‐Pd2/3DOM Al2O3, show higher catalytic activity for soot combustion due to good synergetic effects between gold and palladium. Au/Pd ratio has a significant influence on the chemical states and size of bimetallic nanoparticles. The co‐presence of Au is favorable for the formation of metallic Pd instead of PdO. And the size of Au−Pd bimetallic nanoparticles gradually decreases with increasing Au/Pd ratio. The effect of water in the reaction atmosphere and SO2‐presulfurization of the catalyst on the activity is also studied. It is unexpected that Au2‐Pd2/3DOM Al2O3 catalysts with SO2‐presulfurization has higher catalytic activity than the fresh catalysts. The increased activity is related to the formed surface aluminum sulfate and enhanced acidity.

Engineering low Pd content catalysts for soot combustion through tuning the Pd-SnO2 interface interaction: Disclosing the critical role of dual Pd valence states for the activity

To manufacture efficient and cost-effective catalysts for soot combustion, SnO2 nano-rod (SnO2-Rod), nano-cube (SnO2-NP-Cube) and regular nanoparticles (SnO2-NP) have been designed as supports for Pd. The soot combustion activity ranks as 0.5 % Pd/SnO2-NP-Cube > 0.5 % Pd/SnO2-Rod > 0.5 % Pd/SnO2-NP. The active oxygen amount of the supports increases as SnO2-Rod < SnO2-NP < SnO2-NP-Cube, which affects significantly Pd valence state distributions. On SnO2-NP-Cube, Pd is highly oxidized with 30.3 % Pd4+ and 69.7 % Pd2+. On SnO2-NP, nearly 100 % Pd2+ is present. On SnO2-Rod, Pd is more reduced with 73.4 % Pd0 and 26.6 % Pd2+. The concerted action of surface active oxygen and dual Pd valence states determines the activity. In detail, the active oxygen sites devote directly to soot oxidation via a Mars-van-Krevelen mechanism with a redox-cycle. The presence of dual Pd valence states on 0.5 % SnO2-NP-Cube and 0.5 % Pd/SnO2-Rod can promote this redox-cycle, thereby improving the soot combustion activity evidently.

Alkali/alkaline-earth metal-modified MnOx supported on three-dimensionally ordered macroporous–mesoporous TixSi1-xO2 catalysts: Preparation and catalytic performance for soot combustion

The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot, which is an important component of atmospheric fine particle emissions. Herein, three-dimensionally ordered macroporous–mesoporous TixSi1-xO2 (3DOM-m TixSi1-xO2) and its supported MnOx catalysts doped with different alkali/alkaline-earth metals (AMnOx/3DOM-m Ti0.7Si0.3O2 (A: Li, Na, K, Ru, Cs, Mg, Ca, Sr, Ba)) were prepared by mesoporous template (P123)-assisted colloidal crystal template (CCT) and incipient wetness impregnation methods, respectively. Physicochemical characterizations of the catalysts were performed using scanning electron microscopy, X-ray diffraction, N2 adsorption–desorption, H2 temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed oxidation, and Raman spectroscopy techniques; then, we evaluated their catalytic performances for the removal of diesel soot particles. The results show that the 3DOM-m Ti0.7Si0.3O2 supports exhibited a well-defined 3DOM-m nanostructure, and AMnOx nanoparticles with 10–50 nm were evenly dispersed on the inner walls of the uniform macropores. In addition, the as-prepared catalysts exhibited good catalytic performance for soot combustion. Among the prepared catalysts, CsMnOx/3DOM-m Ti0.7Si0.3O2 had the highest catalytic activity for soot combustion, with T10, T50, and T90 (the temperatures corresponding to soot conversion rates of 10%, 50%, and 90%) values of 285, 355, and 393°C, respectively. The high catalytic activity of the CsMnOx/3DOM-m Ti0.7Si0.3O2 catalysts was attributed to their excellent low-temperature reducibility and homogeneous macroporous–mesoporous structure, as well as to the synergistic effects between Cs and Mn species and between CsMnOx and the Ti0.7Si0.3O2 support.

Inherent Reactivity of Praseodymium-Modified Ceria-Zirconia Catalysts for Oxidation of Soot

In this investigation, modified and pure ceria-zirconia catalysts were prepared by a surfactant-assisted hydrothermal method. Analytical techniques such as Powder X-ray diffraction (XRD), BET-BJH-surface area, Thermogravimetry/differential thermogravimetry (TG/DTG), Raman spectroscopy (RS), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and Temperature Programmed Reduction (TPR) were utilized to characterize the structures of the prepared catalysts. The formation of a cubic fluorite structure of ceria-zirconia was inferred from XRD analysis. The oxidation states of the metals present were studied using XPS. The objective of this work was to investigate the effect of cerium content and the influence of praseodymium in promoting the soot combustion activity of ceria-based catalysts. Our study showed that the order of activity depends on the amount of the cerium and modified metal. Modification of the ceria-zirconia catalysts with praseodymium enhanced the catalytic activity to a great extent. Notably, the reactivity of the soot combustion reaction was found to correlate with the improved redox properties and the synergistic effect of praseodymium and the ceria component.

Revealing the boosting role of NO for soot combustion over CeO2(111): A first-principles microkinetic modeling

Co-feeding NO can show an interesting boosting role in the soot combustion reaction, but the molecular-level mechanism remains unsettled and thus hinders the rational optimization of such an important catalytic system. Herein, a first-principles study integrating with microkinetic model is performed to quantitatively explore the catalytic mechanism of soot combustion on CeO2(111) in the presence of NO, aiming to unravel the origin of promotional effect of NO. The catalytic activities of different N-containing species evolved from NO oxidation, i.e. nitrite/nitrate trapped at O vacancy sites and the surface-bound nitrate, which are the generally supposed species for boosting soot combustion, are explicitly examined. The microkinetic result indicates that the soot combustion activity in the presence of NO at the typical temperature of 600 K is nearly two orders of magnitude higher than that in the absence of NO. Despite the improved reactivities relative to the pristine CeO2(111), we find that these oxidative species themselves are unexpectedly not the most crucial in facilitating soot combustion at the typical experimental condition; the in-situ generated O vacancies from the NO oxidation side-reaction largely enhance the adsorption of more reactive peroxide O22−, which indirectly contribute more to the overall soot combustion efficiency. Moreover, the effects of temperature and NO partial pressure on modulating the soot combustion are discussed with the optimal value provided. These insights deepen understanding of the NO effect on soot combustion and could facilitate the optimization of after-treat system in diesel exhaust emission.

The Effect of Synthesis Methods on Active Oxygen Species of MnOx-CuO in Soot Combustion

The activity of the catalyst is closely related to the synthesis method. Hereon, we prepared a series of XMn1Cu (X = 2, 4, 6, 8) catalysts by hydrolysis driven redox, co-precipitation and hydrothermal synthesis approaches, respectively. The effect of XMn1Cu synthesized by different strategies on soot combustion activity were compared. The results show that the catalysts fabricated by hydrolysis driven redox have excellent performance than the other two methods in soot removal, and the activity follows r-XMn1Cu > h-XMn1Cu > cop-XMn1Cu. The Mn/Cu = 4:1 is the optimal ratio of Cu-Mn composite oxide. Among the materials, the r-4Mn1Cu sample has the best catalytic activity due to the uniform distribution of Mn and Cu, high specific surface area, enhanced content of Mn4+, promoted concentration of lattice defects and oxygen vacancies, and T10, T50 and T90 are 303, 355 and 386 °C, respectively. The repeated experiments present that r-4Mn1Cu has high activity and stability in soot oxidation. Combined with experimental results and characterization, oxygen vacancies and reactive oxygen generation mechanism of XMn1Cu catalyst in soot combustion were further discussed.

Surface acid etching for efficient anchoring of potassium on 3DOM La0.8Sr0.2MnO3 catalyst: An integration strategy for boosting soot and NOx simultaneous elimination

The emission of soot and NOx is one of the most severe environmental issues, and the key factor is the development of catalysts in after-treatment systems. In this study, an innovative non-noble metal catalyst, named HKLSM, was fabricated by etching 3DOM La0.8Sr0.2MnO3 with citric acid and synchronously anchoring potassium salt, for soot and NOx simultaneous removal. The citric acid could not only slightly erode the 3DOM skeleton, thereby beneficial to the dispersion of potassium, but also react with high-valence state Mn to generate abundant coordination unsaturated Mn3+ sites, which could produce more active oxygen species. Moreover, HKLSM showed a higher NOx adsorption capability than the samples that were not subjected to acid etching. This adsorbed NOx could be stored as NO3− species, which could facilitate soot combustion. Among all the as-prepared catalysts, HKLSM demonstrated a competitive soot combustion activity with a T50 value of 368 °C, a TOF value of 3.24 × 10−4 s−1, a reaction rate of 1.87 × 10−7 molg−1s−1, a total NOx to N2 yield of 42.0% and favorable reusability and water-resistance. This integration strategy can rationalize an alternative protocol to soot and NOx simultaneous elimination or even other catalysis systems.

Copper‐Lanthanum Catalysts for NOx and Soot Removal

AbstractThe individual and simultaneous removal of NOx by Storage and Reduction with H2 (H2‐NSR) and combustion of soot have been studied for La and CuLa catalysts. The NOx storage capacity of pure lanthanum oxide is improved either by copper addition or by using a colloidal crystal hard template for the synthesis of a macroporous structure. Although the NOx storage capacity of the CuLa macroporous material is around ten times lower regarding conventional PtBa catalysts, the kinetics of the H2‐NSR cycles are fast enough to allow high NOx removal (until 90 % removal). Lanthanum oxide catalyst prepared with uncontrolled structure has no activity for soot combustion, but the activity increases for a macroporous counterpart prepared using the colloidal crystal template because the macroporous structure improves the soot‐catalyst contact and allows the nitrogen‐oxygen surface groups yielded upon NOx chemisorption to oxidize soot. The soot combustion activity of lanthanum catalysts is also enhanced upon copper loading, because copper improves the NO2‐assisted soot combustion mechanism and favors the chemisorption of NOx, enhancing soot oxidation by nitrogen‐oxygen surface species. Finally, it is demonstrated that the simultaneous removal of NOx by H2‐NSR and soot combustion can be carried out with a CuLa catalyst at 450 °C. The simultaneous removal does not affect the combustion of soot and only has a small effect in NOx removal.