Performance For Soot Combustion Research Articles

Facile preparation of alkali metal‐modified hollow nanotubular manganese‐based oxide catalysts and their excellent catalytic soot combustion performance

AbstractThe soot emitted during the operation of diesel engine exhaust seriously threatens the human health and environment, so treating diesel engine exhaust is critical. At present, the most effective method for eliminating soot particles is post‐treatment technology. Preparation of economically viable and highly active soot combustion catalysts is a pivotal element of post‐treatment technology. In this study, different single‐metal oxide catalysts with fibrous structures and alkali metal‐modified hollow nanotubular Mn‐based oxide catalysts were synthesized using centrifugal spinning method. Activity evaluation results showed that the manganese oxide catalyst has the best catalytic activity among the prepared single‐metal oxide catalysts. Further research on alkali metal modification showed that doping alkali metals is beneficial for improving the oxidation state of manganese and generating a large number of reactive oxygen species. Combined with the structural effect brought by the hollow nanotube structure, the alkali metal‐modified Mn‐based oxide catalysts exhibit superior catalytic performance. Among them, the Cs‐modified Mn‐based oxide catalyst exhibits the best catalytic performance because of its rich active oxygen species, excellent NO oxidation ability, abundant Mn4+ ions (Mn4+/Mnn+ = 64.78%), and good redox ability. The T10, T50, T90, and CO2 selectivity of the Cs‐modified Mn‐based oxide catalyst were 267°C, 324°C, 360°C, and 97.8%, respectively.

New method for the preparation of hierarchical nanotube K0.3xMnxCe1-xOδ catalysts and their excellent catalytic performance for soot combustion

A series of nanofibrous K-Mn-Ce composite oxide catalysts were prepared via a centrifugal spinning method for the first time, and their physicochemical properties were studied. The prepared K0.3xMnxCe1-xOδ metal oxide catalyst, which is a composite of CeO2 and cryptopotassium manganese-type K2-xMn8O16, exhibits a hierarchical nanotube structure with uniform nanoneedles on its surface. During the process of soot oxidation, CeO2 utilizes its unique oxygen storage and release capacity to supply oxygen species. Simultaneously, the excellent redox properties of K2-xMn8O16 effectively promote valence cycling of the active components and produce more active oxygen species. This synergistic effect effectively enhances the intrinsic activity of the catalysts. Among the prepared catalysts, K0.15Mn0.5Ce0.5Oδ exhibits the highest catalytic performance, with 10% (T10), 50% (T50), and 90% (T90) soot conversion temperatures of 267 °C, 309 °C, and 338 °C, respectively, and shows good stability and water and sulfur resistance. Based on their simple preparation, low cost, and good catalytic performance, K0.3xMnxCe1-xOδ composite metal oxide catalysts have good potential in catalytic soot combustion applications.

Boosting catalytic combustion of diesel soot particles over potassium-promoted CoMn-Co3O4 dual spinel structure catalyst

Catalytic oxidation is an effective method to remove soot particles from diesel exhaust, and the key aspect of this technology is to develop highly effective catalysts. In this work, a potassium-promoted dual spinel structure was prepared for soot elimination with the self-sacrificing template strategy. The highest activity was presented by the CoMn-0.2 H-10%K catalyst under a loose contact mode, with the temperature of soot conversion reaching 90% and turnover frequency value of 365 °C and 3.76×10−3 s−1, respectively. The catalyst was found to have a high content of oxygen vacancy and a superior ability for lattice oxygen migration, which led to elevated performance for soot combustion. The formation of K-OMS-2 at the interface between the CoMn spinel and the Co3O4 spinel was one of the reasons for the elevated lattice oxygen migration at low temperatures. This work provides an effective way to prepare transition metal catalysts for soot combustion.

Research Advances in Rare Earth Oxide‐Based Catalysts for Soot Combustion

AbstractEnvironmental issues exert a significant influence on the human life. Soot particles have attracted attention as a major source of pollution. Significant progress has been made in the research of efficient soot combustion catalysts. The distinctive bonding properties on the 4 f orbitals of rare earth elements exhibit excellent catalytic performance for soot combustion. This comprehensive review explores recent advancements in the design of catalysts based on rare earth oxides, with a specific focus on various catalytic materials (La‐based, Ce‐based, Pr‐based and other rare earth elements), synthesis methods, catalyst morphology, catalytic performance and the intricate mechanisms governing their performance in catalytic soot combustion. The activity and selectivity of different rare earth catalysts in various reaction atmospheres are also summarized in the article. Finally, the challenges associated with rare earth oxide‐based catalysts and their potential for future development in the soot combustion are highlighted. This review establishes a fundamental basis for the further design of catalytic materials that exhibit enhanced efficiency and stability.

Low temperature oxidation of diesel soot particles over one-dimensional 2 × 3 tunnel-structured Na2Mn5O10 catalysts

Tunnel-structured manganese oxides have drawn widespread research attention due to their excellent oxidation properties for the soot oxidation reaction. In this study, a series of romanechite Na2Mn5O10 catalysts with a 2 × 3 tunnel structure were synthesized via a facile hydrothermal method. The as-synthesized catalysts were investigated using X-ray diffraction, scanning and transmission electron microscopy, H2 and soot temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed oxidation, X-ray photoelectron spectroscopy, and other measurements. Among all the catalysts, the Na1MnyOδ-120 catalyst exhibited the best catalytic performance for soot combustion, with T10, T50, and T90 values of 281 ℃, 317 ℃, and 343 ℃, respectively, which were considerably reduced to 271 ℃, 310 ℃, and 335 ℃ in the existence of 10% H2O. The results of multiple characterization methods indicated that the Na2Mn5O10 catalysts exhibit good reducibility, strong oxygen adsorption and activation capacity, and NO to NO2 oxidation ability. Moreover, the active sites (Mn and oxygen vacancies) and reaction mechanism (Langmuir–Hinshelwood) were also revealed by in-situ DRIFT and density functional theory calculations results. This study details a new strategy for the design and synthesis of efficient soot oxidation catalysts with practical application prospects.

The Preparation of Mn-Modified CeO2 Nanosphere Catalysts and Their Catalytic Performance for Soot Combustion

With the increasing stringency of environmental protection regulations, reducing the severe pollution caused by soot particles from diesel vehicle exhaust has become a widespread concern. Catalytic purification technology is currently an efficient method for eliminating soot particles, which needs to develop high-activity catalysts. This work uses a two-step hydrothermal method to synthesize MnOx/CeO2 nanosphere catalysts, which have synergistic effects between manganese and cerium, and have high reactive oxygen species. Among them, the MnCe-1:4 catalyst represents the optimal catalytic activity, and the values of T10, T50, and T90 are 289, 340, and 373 °C, respectively. On account of their simple synthetic procedure and low cost, the prepared MnOx/CeO2 nanosphere catalysts have good prospects for practical applications.

The influence of partial substitution of Ce with K in CeMO3 (M = Mn, Fe, Co, Ni, Cu) perovskite catalysts on soot combustion performance

A series of Ce1−xKxMO3 (M = Mn, Fe, Co, Ni, Cu, and x = 0, 0.1, 0.2, 0.3, 0.4) perovskite catalysts were synthesized by citrate sol-gel method, in which A-site element Ce was partially substituted with K. The results showed that the catalytic performance could be significantly improved by partially substituting of Ce with K in CeCoO3 catalyst for soot combustion. Ce0.8K0.2CoO3 perovskite catalyst exhibited a superior catalytic activity, and its corresponding T10, T50, T90 and SmCO2 were 326, 383, 426 °C and 98.6%, respectively. The characterization results indicated that K+ had been successfully incorporated in the perovskite crystal structure. Partially substituting of Ce with K resulted in an increase in specific surface area. It also resulted in the formation of Co4+ in the perovskite catalysts together with abundant presence of oxygen vacancies on the surface. Moreover, it was of great significance to facilitate the activation of lattice oxygen species. In situ DRIFTS result showed that NO2 produced by thermal decomposition of monodentate nitrate species played a key role in soot combustion process.

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.

Effect of oxygen vacancy and highly dispersed MnOx on soot combustion in cerium manganese catalyst

Cerium manganese bimetallic catalysts have become the focus of current research because of their excellent catalytic performance for soot combustion. Two series of cerium manganese catalysts (Na-free catalysts and Na-containing catalysts) were prepared by coprecipitation method and characterized using XRD, N2 adsorption–desorption, SEM, Raman, XPS, H2-TPR, O2-TPD, Soot-TPR-MS and in situ IR. The effects of abundant oxygen vacancies and surface highly dispersed MnOx on soot catalytic combustion of cerium manganese catalysts prepared by different precipitants were analyzed. The activity test results show that the active oxygen species released by a large number of oxygen vacancies in the cerium manganese catalyst are more favorable to the soot catalytic combustion than MnOx which is highly dispersed on the surface of the catalyst and has good redox performance at low temperature. Because the catalytic effect of MnOx on the surface of Na-free catalysts is more dependent on the contact condition between the catalyst and the soot, this phenomenon can be observed more easily under the loose contact condition than under the tight contact condition. The activity cycle test results show that these two series of catalysts show good stability and repeated use will hardly cause any deactivation of the 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.

Ultralight and spongy La–Mn-based perovskite catalysts modified by alkali metals and Ce: facile synthesis and excellent catalytic performance for soot combustion

Soot particles released from diesel engines have been considered as one of the main sources of air pollution, and the elimination of soot particles has become a crucial issue for air purification.

K-modified MnOδ catalysts with tunnel structure and layered structure: Facile preparation and catalytic performance for soot combustion

K-modified MnOδ catalysts with tunnel structure and layered structure: Facile preparation and catalytic performance for soot combustion

Exposed crystal facet tuning of CeO2 for boosting catalytic soot combustion: The effect of La dopant

The exposed crystal facets are crucial to heterogeneous catalysis. Herein, the facet controlled Ce1−xLaxOδ (0 ≤ x ≤ 0.30) nanocomposites have been constructed elaborately via a hydrothermal route and used for soot abatement. The catalysts were characterized by XRD, TEM, Raman, FT-IR, XPS, H2-TPR, and so forth. With the increasing content of La3+, part of CeO2 crystals transformed from nanocubes to nanorods, inducing distinct effects on the catalytic activity. When the concentration of La3+ was lower than 10 %, the exposed facet in the catalyst was (200). After La3+ were further introduced, the facet degraded to (111). La3+ at low concentration would enhance activity by facilitating lattice oxygen delivery and inducing abundant surface oxygen species, especially O-, which were vital to surface sensitive soot oxidation. Nevertheless, excessive La3+ ions would inhibit CO2 desorption due to the generation of La2O2CO3, a strong alkali as a result of phase separation. Among all the catalysts, Ce0.95La0.05Oδ showed the best catalytic performances for soot combustion, with T50 of 375 °C.

Facile preparation and efficient MnxCoy porous nanosheets for the sustainable catalytic process of soot

The pursuit of high-performance is worth considerable effort in catalysis for energy efficiency and environmental sustainability. To develop redox catalysts with superior performance for soot combustion, a series of MnxCoy oxides were synthesized using MgO template substitution. This method greatly improves the preparation and catalytic efficiency and is more in line with the current theme of green catalysts and sustainable development. The resulting Mn1Co2.3 has a strong activation capability of gaseous oxygen due to a high concentration of Co3+ and Mn3+. The Mn doping enhanced the intrinsic activity by prompting oxygen vacancy formation and gaseous oxygen adsorption. The nanosheet morphology with abundant mesoporous significantly increased the solid–solid contact efficiency and improved the adsorption capability of gaseous reactants. The novel design of Mn1Co2.3 oxide enhanced its catalytic performance through a synergistic effect of Mn doping and the porous nanosheet morphology, showing significant potential for the preparation of high-performance soot combustion catalysts.

Synergistic effect of binary Co and Ni cations in hydrotalcite-derived Co2-xNixAlO catalysts for promoting soot combustion

Surface coordination unsaturation cation in hydrotalcite-derived CoAl oxides is crucial to improve catalytic performance during soot combustion. Herein, the hydrotalcites-derived Co2-xNixAlO catalysts were prepared by the co-precipitation method. The characteristic nanosheet structure of hydrotalcite-derived CoAl oxides can promote mass transfer efficiency of the reactants. The cobalt elements partially replaced by nickel elements in hydrotalcite-derived CoAl oxides can induce the formation of coordination unsaturated cations and surface anion defects (oxygen vacancies) for increasing surface area and active site. The synergistic effect of binary Co and Ni ions in hydrotalcites-derived Co2-xNixAlO catalysts can boost adsorption-activation properties for O2 and NO. Hydrotalcites-derived Co2-xNixAlO catalysts exhibit excellent catalytic performances for soot combustion, and their catalytic activity strongly depends on the synergistic effect of binary Co and Ni cations. Among the catalysts, Co1.5Ni0.5AlO catalyst has the highest catalytic activity (T50 = 333 °C, TOF = 1.01 × 10−2 s−1). Based on the characterization results, the catalytic mechanism for soot combustion is proposed: the synergistic effect of binary Co and Ni cations in Co2-xNixAlO catalysts can boost the key step of NO oxidation to NO2. The in-depth understanding on the synergistic effect of Co and Ni cations is meaningful for the development of the ternary hydrotalcite-derived catalysts for soot combustion.

Preparation of Cordierite Monolith Catalysts with the Coating of K-Modified Spinel MnCo2O4 Oxide and Their Catalytic Performances for Soot Combustion

Diesel engines are important for heavy-duty vehicles. However, particulate matter (PM) released from diesel exhaust should be eliminated. Nowadays, catalytic diesel particulate filters (CDPF) are recognized as a promising technology. In this work, a series of monolith Mn1−nKnCo2O4 catalysts were prepared by the simple citric acid method. The as-prepared catalysts displayed good catalytic performance for soot combustion and the Mn0.7K0.3Co2O4 catalyst gave the best catalytic performance among all the prepared samples. The T10 and Tm of Mn0.7K0.3Co2O4-HC catalyst for soot combustion are 310 and 439 °C, respectively. The physical and chemical properties of catalysts were characterized by means of SEM, XPS, H2-TPR, Raman and other techniques. The characterization results indicate that K substitution is favorable for the formation of oxygen vacancies, enhancing the mobility of active oxygen species, and improving the redox properties and so on. In-situ Raman results prove that the strength of Co-O bonds in the catalysts became weak during the reaction at high temperatures. In addition, SEM and ultrasonic test results show that the peeling rate of the coat-layer is less than 5%. The as-prepared catalysts can be taken as one kind of candidate catalyst for promising application in soot combustion because of its facile synthesis, low cost and high catalytic activity.

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.

Boosting diesel soot catalytic combustion via enhancement of solid(catalyst)-solid(soot) contact by tailoring micrometer scaled sheet-type agglomerations of CeO2-ZrO2 catalyst

Solid(catalyst)-solid(soot) contact is a crucial factor in diesel soot catalytic combustion, and rationally optimizing solid(catalyst)-solid(soot) contact is a promising yet challenging pathway for improving catalytic diesel soot combustion performance. Here, we report a micrometer scaled sheet-type CeO2-ZrO2 soot oxidation catalyst. The nitrogen adsorption-desorption result indicates that soot particulates are barely able to enter into the inner pore of the catalyst (average pore size < 20 nm) due to the large size of filamentous soot agglomeration (reaching up to 1 μm). Thus the catalyst-soot contact mainly depends on the catalyst external surface and morphology. Electron microscope images confirm the presence of microsheet agglomerations of the prepared CeO2-ZrO2 catalyst, which is an advantage for enhancing the adherence of soot filaments on catalyst. Compared to common CeO2-ZrO2 particle catalyst, the CeO2-ZrO2 microsheet shows a remarkably higher macrolevel soot combustion performance. Interestingly, the single catalytic site activity (intrinsic activity) of CeO2-ZrO2 microsheet is not enhanced by the micro-structure. Thus the enhanced soot combustion efficiency could be ascribed to the improving of catalyst-soot contact. And therefore, this work suggests that constructing structured catalyst at micrometer level is an efficient way to improve the solid(catalyst)-solid(soot) contact efficiency and thereby boost the diesel soot combustion performance.

Facile preparation of amorphous CenMnOx catalysts and their good catalytic performance for soot combustion

Diesel engines are widely used because of their low fuel consumption, high fuel efficiency, high reliability, and safety. However, the soot particles contained in diesel engine exhaust have become one of the main sources of urban haze, and their elimination has great significance for environmental protection and economics. In the present study, a series of CenMnOx catalysts with different Ce contents and calcination temperatures were successfully synthetized via a simple hydrothermal process, and the physicochemical characteristics of the as-prepared catalysts were investigated. That CenMnOx composite oxides were amorphous, contradicting previous reports that manganese and cerium usually form MnxCe1-xOδ with crystalline structures. Due to Ce doping, the amorphous Ce1MnOx catalysts have higher specific surface area, greater porosity, and better ability to activate oxygen species than pure MnOx catalysts. The amorphous catalysts also exhibit good stability, sulfur and water resistance for catalytic combustion of soot particles. Among the prepared catalysts, Ce1MnOx calcinated at 450 °C has the best catalytic activity, the values of T10, T50 and T90 were 258 °C, 327 °C and 370 °C, respectively. Based on their simple preparation, low cost, and good catalytic performance, the amorphous CenMnOx catalysts show promise for application in soot combustion.

Effect of surface manganese oxide species on soot catalytic combustion of Ce–Mn–O catalyst

Constructing cerium and manganese bimetallic catalysts with excellent catalytic performance for soot combustion is the research frontier at present. In order to find out the key factors for catalytic soot combustion of Ce–Mn–O catalysts, a series of Ce–Mn–O catalysts with different Ce/Mn proportions were prepared by co-precipitation method. The activity test results show that it increases first and then decreases with the increase of Mn content. The best catalytic activity is obtained for Ce0.64Mn0.36 catalyst, which shows a maximum rate temperature (Tm) at 306 °C for CO2 production in TPO curve. Compared with non-catalytic soot combustion, the Tm decreases by more than 270 °C. Systematical characterization results suggest that when the adsorbed surface oxygen, lattice oxygen, specific surface area and total reduction amount of the catalysts reach a certain value, the key factors leading to the difference of catalytic activity become the readily reducible and highly dispersed surface manganese oxide species and contact performance of the external surface. The surface manganese oxide species is beneficial to improving the low-temperature reducibility of catalysts and the porous surface is conducive to the contact between catalyst and soot. Furthermore, for the soot combustion reaction containing only O2, the promoting effect of Mn4+ is not obvious.