Soot Oxidation Activity Research Articles

Plasma treatment on flame soot: view from nanostructure and reactivity of soot

In recent years, the use of plasma for pollutant emission control has an expected potential. In this study, soot particles from flames were sampled from an ethylene inverse diffusion flame, which were placed in a self-designed dielectric barrier discharge plasma device for reaction treatment. The nanostructure and oxidation reactivity of soot particles after plasma treatment were evaluated by transmission electron microscopy, Raman spectroscopy, X-ray diffraction analysis and X-ray photoelectron spectroscopy. With 16 kV, 2.5 kHz as an example, with the treatment of plasma, the fringe length decreases (1.3% and 9.6%), and the fringe tortuosity increases (1.1% and 8.7%) in both high-maturity and low-maturity soot particles, which means that the oxidation activity of soot is enhanced after plasma discharge. Raman spectra, X-ray diffraction analysis spectra and X-ray photoelectron spectroscopy spectra have confirmed this phenomenon, especially the oxidation activity of soot particles under the action of plasma at high maturity is more obvious. It is worth noting that the enhancement of soot oxidation activity after plasma discharge has certain limitations, that is, the oxidation activity will not continue to increase after it is enhanced to a certain intensity, which may be related to the selection of Ar as the atmosphere gas.

The effect of supported metal Species on soot oxidation over PGM/CeO2-ZrO2

Abstract Herein is studied the soot oxidation over platinum group metal oxide/CeO2–ZrO2 (PGM/CZ) catalysts. The ability to capture gas-phase oxygen was in sequence of Ru/CZ > Rh/CZ > Ir/CZ > Pt/CZ > Pd/CZ. A soot oxidation test by TG-DTA showed that Ru/CZ, Rh/CZ, and Ir/CZ are highly active catalysts. It was found that there is a good correlation between the ability to capture gas-phase oxygen and soot oxidation activity. TEM observation revealed that soot oxidation mainly occurs at the interface between soot and CZ surfaces. The Ea values and soot oxidation test using labelled oxygen suggest that highly active catalysts oxidize soot by CZ lattice oxygen. For Ir/CZ, soot oxidation at 270 °C occurred due to the reduction by soot. Ru/CZ and Rh/CZ captured gas-phase oxygen spontaneously below 250 °C, resulting in soot oxidation at 270 °C. H2-TPR results suggest that the reactivity of lattice oxygen in the CZ surface, improved by PGM, is also related to soot oxidation activity. This suggests that the ability to capture gas-phase oxygen and the reactivity of lattice oxygen in the CZ surface determine the soot oxidation activity, and that Ru, Rh, and Ir have the effect of enhancing these properties.

Catalytic performance of Cs-V-based non-noble soot oxidation catalyst used for DPF and its enhancement by cerium addition

Non-noble metal catalysts have great potential for controlling soot emissions due to their effective oxidation properties and low cost. This study investigated the characteristics of Cs-V-based non-noble metal soot catalyst and Ce doping enhancement effect through comprehensive characterization of physicochemical properties, catalytic activity evaluation, and density functional theory (DFT) theoretical calculations. The results demonstrate that Ce doping improves the degree of surface particle aggregation and the spatial distribution morphology of Cs-V-based catalyst, with a 36.7 % increase in the specific surface area. Additionally, Ce doping enhances the probability of oxygen adsorption and dissociation activation on the Cs-V-based catalyst, accelerating the soot-oxidation process, improving the soot-oxidation activity, with a decrease in the characteristic temperature T10 (temperature at 10 % conversion rate of soot) from 349.7 ℃ to 281.1 ℃, and decreases the activation energy for soot-oxidation to 5.8 kJ/mol. DFT calculations reveal that Ce doping strengthens the pulling effect of interatomic chemical bonds, facilitating the removal of oxygen atoms and dissociated reactive oxygen (Oasd), resulting in an increase in the adsorption energy of C4 molecules and a shorter bond length between C4 molecules and the catalytic surface, facilitating the desorption of post-oxidation soot products.

Insight into the mechanism of solution organic fractions on soot oxidation activity enhancement

The particulate matter and soluble organic fraction emitted by diesel engine are hazardous to environment and human health. Exploring the effect mechanism of soluble organic fraction on soot oxidation is beneficial for reducing the emissions. In this study, the effects of four different types of soluble organic fractions on the soot oxidation activity and physicochemical properties are investigated. The results show that the attachment of oxygen-containing soluble organic fractions enhances the soot oxidation and reduces the peak characteristic temperature. However, the low volatility soluble organic fractions without oxygen element inhibit soot oxidation. Additionally, the high volatility soluble organic fractions without oxygen element elicit limited effects on soot oxidation. the contents of aliphatic C-H functional groups, carbonyl CO functional groups, and carboxylic acid O-CO functional groups significantly increase after adding oxygen-containing soluble organic fractions, while the limited increase in functional groups is observed in soluble organic fractions without oxygen element. Solid soluble organic fractions adhere to soot particles in the form of small particles, leading a reduction in the initial particle size distribution, while liquid soluble organic fractions exhibit block and chain shapes around the soot particles, which makes the initial particle size distribution increasing. Moreover, the attachment of all soluble organic fractions disrupts the surface order of soot particle, leading to a decrease in soot graphitization. This study is beneficial for revealing the interaction mechanism between soot and soluble organic fractions.

Role of morphology in improving the catalytic performance of ZnCo2O4 for soot oxidation

The extent of interaction between carbon and catalyst profoundly shapes soot oxidation results. The catalyst configuration notably influences the frequency of contact points in solid–solid interactions. This investigation studies the impact of three distinct ZnCo2O4 catalyst morphologies and their redox property on soot oxidation. The formation of the cubic phase of ZnCo2O4 via three distinct methods was revealed during XRD analysis. SEM analysis unveiled varying morphologies, including rod-shaped, rose petal-shaped, and bead-like structures. Notably, ZnCo2O4 exhibiting bead-like morphology demonstrated heightened levels of chemisorbed oxygen species which was observed during XPS analysis. The presence of Co2+ and Co3+ occupied at octahedral site ZnCo2O4 acted as the active sites for soot oxidation. With continuous redox property (Co 3+ → Co 2+) leading to the generation of active oxygen species and with an added advantage of surface morphology, the M2 sample (with bead-like morphology) exhibited superior soot oxidation activity, which is evident by its T50% value of 402 °C. This study underscores the essential role of catalyst morphology in influencing soot oxidation activity. Through a comprehensive array of structural, morphological, and catalytic analyses, this work sheds light on the correlation between catalyst architecture and enhanced soot oxidation performance.

Investigation of sodium–manganese oxides with various crystal phases for the efficient catalytic removal of diesel soot particles

Sodium–manganese oxides with various crystal phases (Na2Mn5O10, Na2Mn3O7, and Na4Mn9O18) were synthesized using a facile sol-gel method, and applied in the catalytic purification of soot particles from diesel engines. In this study, as-prepared samples with a single Na2Mn3O7 phase exhibited higher soot oxidation activity, with the lowest T10, T50, and T90 values of 279 ℃, 320 ℃, and 349 ℃, respectively. Numerous characterization techniques reveal that the Na2Mn3O7 catalysts have superior reducibility, NO oxidation, and storage capacity compared with the other crystal phases. In the meantime, the Na2Mn3O7 catalyst surface possesses a greater abundance of oxygen vacancies because of the emergence of Mn3+, which serve as crucial active sites during the dynamic cycling process of gaseous oxygen adsorption and activation. Moreover, the E-R reaction mechanism for soot combustion over the steps of (100) crystal plane of Na2Mn3O7 catalysts is proposed based on density functional theory (DFT) calculations and multiple characterization results. This study presents a facile and cost-efficient method for designing and preparing superior performance sodium–manganese composite oxides for soot combustion.

Catalytic activity of Zr/CeO2-Al2O3 catalyst for diesel soot oxidation: synthesis, characterization, and performance evaluation.

Diesel soot is a significant contributor to air pollution. Soot particles present in diesel engine exhaust have a negative impact on the environment and human health. Diesel oxidation catalysts (DOCs) and diesel particulate filters (DPFs) currently use noble metal-based catalysts for soot oxidation. Due to the use of noble metals in the catalyst, the cost of diesel after-treatment systems is steadily rising. As a result, diesel vehicles have become commercially less viable than gasoline vehicles and electronic vehicles. The study focuses on an alternative diesel oxidation catalyst with efficiency similar to that of a noble metal catalyst but with a much lower cost. CeO2-Al2O3 catalysts are known for their oxygen storage capacity and high redox activity, making them suitable for soot oxidation. Adding Zr to these catalysts has been shown to influence their structural and chemical properties, significantly affecting their catalytic behavior. Therefore, the current study is focused on using Zr/CeO2-Al2O3 as a substitute for noble metal-based catalysts to enhance its performance for diesel soot oxidation in automotive exhaust. Evaporation-induced self-assembly (EISA) was used to prepare 1, 3, and 5 weight (wt) % Zr supported mesoporous CeO2-Al2O3 catalysts. Morphological, structural, and physicochemical properties of the synthesized catalysts were examined using Brunauer-Emmett-Teller (BET) absolute isotherm, Scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Temperature programmed reduction (TPR), and Temperature-programmed desorption of ammonia (NH3-TPD). XRD, BET, and SEM data confirmed that the catalysts were mesoporous and low-crystalline with a high surface area. The soot oxidation activity of the catalysts was evaluated using a thermogravimetric analysis (TGA) technique. The loose contacts soot oxidation activity test suggested that 50% oxidation of soot occurred at 390°C in the absence of a catalyst. T50 of CeO2-Al2O3 catalyzed soot oxidation was 296°C. Adding Zr to the catalyst significantly improved catalytic activity for diesel soot oxidation. We observed a further drastic change in T50 of soot over 1, 3, and 5% Zr/CeO2-Al2O3, which were 220°C, 210°C, and 193°C, respectively. According to these results, incorporating Zr into the CeO2-Al2O3 catalyst significantly improved the oxidation process of soot.

Soot oxidation activity and stability of NMxCe1-xO2-y nanoparticles (NM = Pd, Rh, Ru) supported on functionalized alumina

NMxCe1-xO2-y (NM = Pd, Rh, Ru) nanoparticles deposited on functionalized alumina were studied as catalysts of soot oxidation reaction. The activity and stability of ceria nanoparticles increased with the dopant content and adequate method of the alumina functionalization. Using the support functionalized with a decane layer increased the nanoparticles' dispersion and improved the catalyst stability. After the first run of the reaction, some deactivation occurred in all doped systems, while in the subsequent runs, the catalysts were stable. The deactivation was caused by the shape and structure changes (decrease in the number of oxygen defects, exposure of less active (111) planes, and formation of large NMOx particles). The catalyst containing ceria particles doped with x = 0.05 ruthenium was the most active in all three soot oxidation runs with T50% = 448, 480, and 483 °C.

Effects of ammonia addition on the soot nanostructure and oxidation reactivity in n-heptane/toluene diffusion flames

Co-firing NH3 with conventional hydrocarbon fuels is an important approach for reducing CO2 emissions in existing combustion systems. Besides CO2, the blending of NH3 would also notably affect soot formation and its oxidation behaviors. In the present study, we focus on the effects of NH3 on the nanostructure and oxidation characteristics of soot produced in diffusion flames of n-heptane/toluene mixtures. Two configurations of laminar co-flow diffusion flame, including both normal and inverse diffusion flames (NDF and IDFs), were used for investigation. High-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (Raman), and Thermogravimetric analysis (TGA) were employed for soot characterization. The HRTEM and Raman spectra showed that with the increase of NH3 blending ratio, the fringe length (La) and the degree of graphitization decreased while the microcrystal tortuosity (Tf) increased. The results are in consistent with TGA analysis which suggests the promoting effects of NH3 on the soot oxidation reactivity. Difference between NDF and IDF with respect to the soot nanostructure and oxidation activity were discussed. It is our hope that the present results could deepen our understanding on the effects of NH3 on soot nanostructure and oxidation behavior and benefit the design of particulate filters for combustion devices fueled with hydrocarbon/NH3 mixtures.

Effect of Metal Oxides (CeO2, ZnO, TiO2, and Al2O3) as the Support for Silver-Supported Catalysts on the Catalytic Oxidation of Diesel Particulate Matter.

This work presented the influence of metal oxides as the support for silver-supported catalysts on the catalytic oxidation of diesel particulate matter (DPM). The supports selected to be used in this work were CeO2 (reducible), ZnO (semiconductor), TiO2 (reducible and semiconductor), and Al2O3 (acidic). The properties of the synthesized catalysts were investigated using XRD, TEM, H2-TPR, and XPS techniques. The DPM oxidation activity was performed using the TGA method. Different states of silver (e.g., Ag° and Ag+) were formed with different concentrations and affected the performance of the DPM oxidation. Ag2O and lattice oxygen, which were mainly generated by Ag/ZnO and Ag/CeO2, were responsible for combusting the VOCs. The metallic silver (Ag°) formed primarily on Ag/Al2O3 and Ag/TiO2 was the main component promoting soot combustion. Contact between the catalyst and DPM had a minor effect on VOC oxidation but significantly affected the soot oxidation activity.

Highly Reactive Peroxide Species Promoted Soot Oxidation over an Ordered Macroporous Ce0.8Zr0.2O2 Integrated Catalyzed Diesel Particulate Filter.

Particulate matter, represented by soot particles, poses a significant global environmental threat, necessitating efficient control technology. Here, we innovatively designed and elaborately fabricated ordered hierarchical macroporous catalysts of Ce0.8Zr0.2O2 (OM CZO) integrated on a catalyzed diesel particulate filter (CDPF) using the self-assembly method. An oxygen-vacancy-enriched ordered macroporous Ce0.8Zr0.2O2 catalyst (VO-OM CZO) integrated CDPF was synthesized by subsequent NaBH4 reduction. The VO-OM CZO integrated CDPF exhibited a markedly enhanced soot oxidation activity compared to OM CZO and powder CZO coated CDPFs (T50: 430 vs 490 and 545 °C, respectively). The well-defined OM structure of the VO-OM CZO catalysts effectively improves the contact efficiency between soot and the catalysts. Meanwhile, oxygen vacancies trigger the formation of a large amount of highly reactive peroxide species (O22-) from molecular oxygen (O2) through electron abstraction from the three adjacent Ce3+ (3Ce3+ + Vö + O2 → 3Ce4+ + O22-), contributing to the efficient soot oxidation. This work demonstrates the fabrication of the ordered macroporous CZO integrated CDPF and reveals the importance of structure and surface engineering in soot oxidation, which sheds light on the design of highly efficient PM capture and removal devices.

Effect of SO2 on the soot oxidation activity of flame spray pyrolysis-made manganese oxide catalyst in gasoline model exhaust

AbstractThis study deals with the effect of SO2 on the soot oxidation activity of flame spray pyrolysis-prepared manganese oxide in gasoline model exhaust. The catalyst was exposed to 15 and 30 ppm SO2 at 250 °C and was characterized by N2 physisorption, SO2-TPD, O2-TPD, DRIFTS, XPS and PXRD. It was shown that the SO2 adsorption results in the formation of surface sulfate, while the uptake increased from 26 to 45 μmol/g with growing sulfur content of the model exhaust. The sulfur adsorption reduces the mobility and availability of oxygen on the catalyst thus inhibiting the oxygen transport from gas phase over the catalyst to the contact points of the soot. Consequently, the soot oxidation activity, investigated with tight contact blends of catalyst and soot, decreases with inclining amount of sulfate. Finally, the sulfate species were mostly removed by thermal treatment at 705 °C, which additionally provoked catalyst sintering. As a result, the catalytic performance of the de-sulfated catalyst was slightly lower compared to the sulfated sample.

Effect of Calcination Temperature on Soot Oxidation Activity by Pure and La-doped CeO2 (Ce1−xLaxO2) Synthesized via Orange Peel Extract

Effect of Calcination Temperature on Soot Oxidation Activity by Pure and La-doped CeO2 (Ce1−xLaxO2) Synthesized via Orange Peel Extract

Ceria-Terbium-based electrospun nanofiber catalysts for soot oxidation activity and its kinetics

BackgroundCeria-based materials have an excellent potential to be catalysts for catalytic three-way converters in the automobile industry. Developing Ceria-based nanofiber catalysts can be a significant approach for further exploring the application of these materials in automobile industries. MethodsIn this study, Ag, Cu, or Co doped Ceria–Terbium nanofibers were synthesized using the electrospinning technique. The obtained nanofiber catalysts were characterized using FE-SEM, XRD, FT-Raman Spectroscopy, and BET-BJH analysis and tested for soot oxidation activity and its kinetics. Significant findingsFE-SEM examination reveals that the obtained nanofibers have a diameter ranging from around 100 to 600 nm. CeTbCo nanofibers exhibited a reduced particle size and enhanced pore formation. The XRD investigation revealed that all the nanofibers displayed a face-centered fluorite structure of CeO2. In Raman spectroscopy analysis, CeTbCo nanofibes showed the emergence of a secondary Co3O4 phase. The CeTbCo nanofiber catalyst showed better SBET (specific surface area) (66 m2/g) and average pore size (12.08 nm) and total pore volume (0.223 cc/g)), better soot oxidation activity (T50 = 347 ℃) than other nanofiber catalysts. The CeTbCo nanofiber catalyst exhibited an activation energy of 132 kJ mol−1 and a pre-exponential factor (ln (A)) of 25.63 min−1.

Modification of SmMn2O5 Catalyst with Silver for Soot Oxidation: Ag Loading and Metal–Support Interactions

A series of Ag-modified manganese-mullite (SmMn2O5) catalysts with different Ag contents (1, 3, and 6 wt.%) were prepared via a citric acid sol–gel method for catalytic soot oxidation. The catalysts were characterized by powder X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Raman spectroscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy analysis (HRTEM), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR). The soot oxidation activity of the mullite was significantly promoted by the addition of silver and affected by the loading amount of the metal. Herein, the influences of silver loading on the metal size distribution and its interactions with the mullite were studied. Based on these characterizations, a possible soot oxidation reaction mechanism was proposed for silver-modified SmMn2O5.

Improved catalytic performance of Ag-doped K-OMS-2 for soot oxidation

The catalytic behaviours of pure K-OMS-2 and Ag-doped K-OMS-2 catalysts (5% Ag doping) synthesized using the hydrothermal method are the focus of investigation in this study. To characterize the catalytic performance of these synthesized catalysts, a combination of analytical techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and Soot Temperature Programmed Reduction (Soot TPR), were employed. The analysis of the prepared samples via XRD revealed a nanocrystalline tetragonal structure, with crystal sizes measuring approximately 22.4 nm. Further examination of the samples using Field Emission Scanning Electron Microscopy (FESEM) unveiled nanorods with dimensions of 213 nm in length and 32 nm in width for K-OMS-2. In comparison, Ag-doped K-OMS-2 displayed nanorods with dimensions of 290 nm in length and 26 nm in width. Notably, the incorporation of Ag+ ions into the K-OMS-2 framework led to an increase in the intensities of the 771 and 527 cm−1 bands when compared to the pure K-OMS-2. This increase can be attributed to the replacement of K+ ions with Ag+ ions in the structure. Furthermore, the introduction of Ag+ ions into the K-OMS-2 framework significantly influenced its catalytic activity for soot oxidation, as evidenced by the augmentation of surface-adsorbed and lattice oxygen radicals, as observed in the results of Soot TPR. The doped sample exhibited substantially enhanced catalytic activity for soot oxidation, as indicated by its low T50 of 370 °C. In addition, the incorporation of the dopant was found to enhance the thermal stability of the catalyst.Graphical abstract

Investigation of the physicochemical properties of soot subjected to non-catalytic and CeO2-catalytic aging under sequential aerobic and anaerobic exhaust-like conditions simulating the transition from engine operation to cessation

Understanding the physicochemical properties of aged soot particles is crucial for enhancing diesel particulate filter (DPF) regeneration strategies. This study examines the physicochemical properties of such soot subjected to both non-catalytic and CeO2-catalytic aging, utilizing a fixed bed test bench where soot samples are aerobically aged at 300–500 °C for 30–90 min before being cooled to ambient temperature under anaerobic conditions. The results indicate that sequential aging at 300–400 °C has minimal impact on soot oxidation activity, with a slight reduction in ignition temperature compared to nascent soot. Concurrently, there is a notable decrease in soot agglomeration, resulting in reduced macropore sizes ranging from 100 nm to 210 nm. The effects of non-catalytic and catalytic aging on soot oxidation activity diverge significantly at 500 °C. The crystallite arrangement in the soot particles takes precedence over oxidation activity, despite the formation of numerous pores post aging above 400 °C. Graphitization in non-catalytically aged soot increases, whereas it decreases following catalytic sequential aging. Post sequential aging at temperatures ranging from 300 to 500 °C, a noticeable shift occurs in soot particles, characterized by the depletion of CO functional groups and concurrent emergence of CO functional groups. Moreover, the presence of catalysts during this aging process markedly enhances the reduction of CO functional groups.

The calcination temperature effect on CeO2 catalytic activity for soot oxidation: a combined experimental and theoretical approach

The catalytic efficiency of CeO2 in soot oxidation was significantly affected by its grain morphology and calcination temperature.

Why Ceria Nanoparticles Obtained from Ce-MOFs Exhibit Higher Catalytic Efficient in Soot Combustion? Understanding the Role of Intrinsic Properties of a Cerium-Organic Framework to Produce CeO2

Metal-organic framework (MOF) derivatives, such as porous metal oxides with controlled morphology have received great attention for applications in various fields. In this paper, the experimental results show that porous CeO2 with high specific surface area (90.5 m2 g-1) and nanorod morphology can be obtained by calcining a Ce-MOF template at optimized temperature (300-500 °C). The formation mechanism of this porous structure as well as the influence of the calcination temperature are well explained by taking into account thermal behavior and intrinsic structural features of the Ce-MOF precursor. We employed the oxides formed as heterogeneous catalysts to reduce the soot originating from the incomplete combustion of diesel or diesel/biodiesel blends. The CeO2 materials exhibit outstanding catalytic activity, lowering the temperature of soot combustion from 610 to 370 °C. Compared with similar work, our catalyst exhibits enhanced soot oxidation activity, making it highly promising for diesel particulate filter applications. Such outstanding catalytic performance of the porous CeO2 nanorods benefits from their large specific surface area, and morphological and structural characteristics.

Cerium Doping Effect in 3DOM Perovskite-Type La2−xCexCoNiO6 Catalysts for Boosting Soot Oxidation

Herein, we present an in-depth investigation into the enhancement of catalytic soot oxidation through cerium-doped three-dimensional ordered macroporous (3DOM) La-Co-Ni-based perovskites synthesized with the colloidal crystal template (CCT) method. The 3DOM structure significantly contributes to the accessibility and interaction efficiency between soot and catalyst. Based on the results of powder X-ray diffraction (XRD), N2 adsorption-desorption measurements, scanning electron microscopy (SEM), temperature-programmed oxidation of NO (NO-TPO), temperature-programmed reduction of H2 (H2-TPR), in situ infrared Fourier transform spectroscopy (In-situ DRIFTS), and temperature-programmed oxidation (TPO) reactions, the role of cerium doping in modifying the structural and catalytic properties of 3DOM perovskite-type La2−xCexCoNiO6 catalysts was investigated systematically. The optimized cerium doping ratio in La2−xCexCoNiO6 catalysts can improve the microenvironment for efficient soot-catalyst contact, enhancing the catalytic activity of soot oxidation. Among the catalysts, the 3DOM La0.8Ce1.2CoNiO6 catalyst shows the highest catalytic activity for soot oxidation, whose T10, T50, and T90 values are 306 °C, 356 °C, and 402 °C, respectively. The mechanism of the cerium doping effect for boosting soot oxidation is proposed: The doping of Ce ions can increase the surface oxygen species, which is the main active species for promoting the key step of NO oxidation to NO2 in catalyzing soot oxidation. This research provides a new strategy to develop high-efficient non-noble metal catalysts for soot oxidation in pollution control and sustainable environmental practices.