Diesel Soot Particles Research Articles

Coupling Effect of Elemental Carbon and Organic Carbon on the Changes of Optical Properties and Oxidative Potential of Soot Particles under Visible Light.

Soot particles, coming from the incomplete combustion of fossil or biomass fuels, feature a core-shell structure with inner elemental carbon (EC) and outer organic carbon (OC). Both EC and OC are known to be photoactive under solar radiation. However, research on their coupling effect during photochemical aging remains limited. This study examines how the optical properties and oxidative potential (OP) of wood, coal, and diesel soot particles with varying EC and OC levels are affected by exposure to visible light. Wood soot, which has the highest OC content, showed the most significant changes in both optical properties and OP, indicating its highest sensitivity to visible light aging. Molecular composition analysis revealed that the reduction of polycyclic aromatic hydrocarbons (PAHs) and methyl-PAHs primarily affects the optical properties, while oxygenated PAHs play a major role in OP. Combined with the results from reactive oxygen species detection, it is suggested that EC initiates photoreactions by generating superoxide anions, while OC undergoes compositional changes that result in subsequent atmospheric effects. These findings enhance our understanding of the photochemical aging process of soot particles and their implications for climate and health.

Retraction: Effects of thermal aging atmospheres on oxidation activity, element composition and microstructure of diesel soot particles.

[This retracts the article DOI: 10.1039/D3RA05340G.].

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.

Boosting the removal of diesel soot particles by regulating the Pr−O strength over transition metal doped Pr6O11 catalysts

The content of active lattice oxygen and oxygen vacancies is crucial for the catalytic oxidation of soot. Herein, we adjust the Pr-O bond strength in Pr6O11 by doping several common transition metals (Mn, Fe, Co, Ni) to promote the formation of oxygen vacancies and the activation of lattice oxygen. This strategy does not compromise its crystal structure, allowing for improved catalytic performance while maintaining stability. The Mn-doped Pr6O11 catalyst shows the best soot catalytic oxidation performance. Its T50 (the temperature of soot conversion reaching 50 %) value is 396 °C under loose contact. Further characterizations and density functional theory (DFT) calculations demonstrate that PMO possesses a large specific surface area. Additionally, the weakening the strength of the Pr-O bond leaded to an increase in oxygen vacancies, which in turn enhanced the redox ability of catalyst. This work will provide a reference for the development of Pr-based catalysts for soot combustion.

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.

Enhanced oxidative potential and cytotoxicity of high-temperature treated model soot particles due to carbonaceous core oxidation

When diesel soot particles experience high-temperature treatment during exhaust purification aiming to reduce emission, their physicochemical properties and toxicity would change as well. However, rare studies investigated the relationship between properties and health effects of soot under high temperatures. This study compared the physicochemical properties, oxidative potential (OP, dithiothreitol (DTT) method), and cytotoxicity of model diesel soot before and after 300°C and 500°C treatments in air. It was observed that the oxygen-containing functional groups, environmental persistent free radicals, surface area and pore volume increased a lot after the 500°C process, accompanied with the appearance of hollow core and decreased particle size in the images collected by high-resolution transmission electron microscopy, indicating the deep oxidation into carbonaceous core of soot. In addition, the enhancements of OPDTT and cytotoxicity were in accordance with the changes in physicochemical properties. The toxic increment at 500°C was the most due to core oxidation, whether it was compared with 300°C heating or the surface oxidation of light irradiation and ozone aging, implying that carbonaceous core oxidation caused worse health damage. Hence, it is necessary to consider the impact of widely used diesel exhaust treatment involving high temperatures, considering the potential toxicity of the resulting particles.

Study on the morphology, nanostructure and fragmentation properties of diesel and diesel-DMM soot particles oxidized in the air/air-NO environment

As an alternative fuel for diesel engines, dimethoxymethane (DMM) has attracted wide attention in recent years, but its impact on the post-treatment process of diesel exhaust particles has been rarely studied. To get a better understanding of the oxidation kinetics of soot in diesel particulate filters (DPFs), the oxidation process of soot emitted from a modern compression ignition (CI) fueled by diesel (D100) and its blend with 11 vol% dimethoxymethane (DMM11) at the same working conditions were investigated by a thermogravimetric analyzer in the air and air-NO atmospheres in this study, respectively. Soot samples at different oxidation degrees (0 %, 20 %, 50 % and 80 % mass loss) were tested by a high-resolution transmission microscopy to characterize the variations of physical properties (morphology, fractal dimension, primary particle diameter and nanostructure) and oxidation-induced fragmentation properties over the oxidation process. The results showed that DMM11 soot had higher oxidation reactivity than D100 soot, and the oxidation reactivity of soot was enhanced by NO involved in the air atmosphere. During the oxidation process, the fractal dimension of D100 and DMM11 soot aggregates gradually increased, and the number and diameter of the primary particles in an aggregate became smaller. This variation trends became more obvious with the presence of NO in the air environment. The nanostructures of D100 and DMM11 soot particles gradually become ordered (characterized by longer fringe length, narrower separation distance and less tortuosity) as the oxidation proceeds. While, when NO added in the air atmosphere the possibility of microcrystals oxidation inside the particles decrease to slow down the getting-ordered rate of soot. Moreover, the fragmentation probability of D100 and DMM11 soot aggregates decreases gradually as oxidation proceeds. During the oxidation process, the probability of primary particle fragmentation for D100 soot increases continuously, while the probability of DMM11 primary soot particles fragmentation showed an increase-then-decrease trend. Compare with D100 soot, DMM11 soot are more likely to occur the fragmentation behavior over the oxidation process. It is worth noting that the addition of NO to the air atmosphere increases the possibility of aggregate fragmentation, while it decreases the possibility of primary particle fragmentation. This work can provide theoretical basis for the development of high efficiency purification technology for diesel exhaust particles.

Pressurized liquid extraction and gas chromatography/mass spectrometry for determination of nitrated polycyclic aromatic hydrocarbons adsorbed on refractory diesel particles

A pressurized liquid extraction (PLE) technique was evaluated in this study and optimized using response surface methodology (RSM) for the determination of polycyclic aromatic hydrocarbons and their nitro derivatives from diesel particulate matter. A central composite design (CCD) was applied for the study of three parameters (temperature, nature of solvent and static time) and the optimal conditions were determined for a time of 9 min and a temperature of 145 °C and dichloromethane as extraction solvent. With the GC/MS analytical technique, the limits of detection (LOD) obtained range from 0.3 to 1.5 µg.L-1 for PAHs and from 4.6 to 8 µg.L-1 for nitrated PAHs. Also, this method allowed excellent recoveries of NPAH adsorbed on diesel soot particles (R ≥ 90%) using a mixture of solvents (1% acetic acid in pyridine). The PLE process developed in this research is quantitative and reproducible while using much less solvent than conventional extraction methods.

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.

84 Effectiveness of Protective Measures—Diesel Exhaust in Garages of Fire Engines Vehicles and Rescue Services

Abstract Diesel exhaust is a complex mixture of soot particles and many gaseous components. Meanwhile, occupational exposure limits (OEL) have been derived for many of these constituents in Europe. Normally, vehicles of fire brigades and rescue units are parked in garages. To ensure readiness for action, they are connected to the power supply system. If they vehicles move out or return to the garage employees may be exposed to diesel engine emission. We have performed measurements in 7 emergency rescue services and 5 fire-fighting stations to assess the exposure to hazardous substances and compare the effectiveness of protective measures.During the measuremnts the different exhaus emission standards and different type of technical protection measure have been compared. The results of the measurements show, that exposure of the employees should be considered as short-term exposure. The most critical substances are diesel soot particles and nitrogen oxides. Especially, for nitrogen monoxide exceedings of the short-term exposure limit value (STELV) have been measured. It was found, that exposure to diesel soot particles decreased from exhaust emission standard EURO 1 to EURO 6. On the other hand, exposure to nitrogen oxides increased for the newer emission standards. The most effective technical protective measure is a trailing extraction system, which should be applied when driving into tho garage, during parking up to moving out, when it should be removed automatically. Alternatively, a vertical transverse system may be effective, but should be assessed for each garage under worst case conditions.

Indoor air aerosol modeling and evaluation based on simulation chamber experiments

High levels of particulate matter (PM) are observed in indoor environments and are of great concern to human health. INCA-Indoor is an indoor air quality (IAQ) model that is able to simulate more than 1200 gaseous species in several rooms of a building. The present study details the aerosol module of this model, which is implemented to simulate aerosol formation by the nucleation of gaseous species, the growth of particles by coagulation and condensation, their deposition on surfaces, and their exchanges with the outdoors and between rooms. To assess the performance of the new modeling system, the simulations are compared with measurements from atmosphere simulation chambers obtained from the EUROCHAMP-2020 database. Two different types of processes are studied: the growth of diesel soot in the AIDA chamber and secondary organic aerosol (SOA) formation and evolution following the ozonolysis of α-pinene in the EUPHORE chamber. INCA-Indoor nicely reproduces the evolution of the number of diesel soot particles, their size distribution during growth by coagulation, and their deposition surfaces. The model also nicely reproduces the formation of aerosols from the ozonolysis of α-pinene, the competitive growth processes, condensation and coagulation, and aerosol deposition. The simulations confirm previous experimental findings and associated assumptions regarding aerosol formation by ozonolysis.

Conversion of Hazardous Diesel Soot Particles into a Novel Highly Efficient 3D Hydrogel for Solar Desalination and Wastewater Purification.

Diesel particulate matter (DPM) generated as vehicular exhaust is one of the main sources of atmospheric soot. These soot particles have been known to cause adverse health problems in humans and cause acute environmental problems. Despite great efforts for minimizing soot production, research on the disposal and recycling of inevitable diesel soot is scarce. However, DPM consists mainly of carbonaceous soot (DS) that can be easily utilized as a photothermal material for solar desalination. Recently, interfacial solar steam generation using three-dimensional (3D) structures has gained extensive attention. 3D-structured hydrogels have exhibited incredible performance in solar desalination owing to their tunable physicochemical properties, hydrophilicity, intrinsic heat localization, and excellent water transport capability. Herein, a novel DS-incorporated 3D polyvinyl alcohol (PVA)-based hydrogel is proposed for highly efficient solar desalination. The polymer network incorporated with purified DS (DSH) achieved an excellent evaporation rate of 3.01 kg m-2 h-1 under 1 sun illumination due to its vertically aligned water channels, hydrophilicity, and intrinsic porous structure. In addition, the DSH-PVA hydrogel could generate desalinated water efficiently (2.5 kg m-2 h-1) with anti-salt fouling properties. The present results would motivate the utilization and recycling of waste materials like DS as photothermal materials for efficient, low-cost, and sustainable solar desalination.

Effects of thermal aging atmospheres on oxidation activity, element composition and microstructure of diesel soot particles.

As an emission control device for diesel engines, DPF plays an important role in reducing particulate matter emissions. The research work on soot thermal aging will help optimize DPF regeneration strategies, improve regeneration efficiency, and promote the progress of engine emission control technology. In order to explore the influence of thermal aging under different atmospheres on particle physicochemical characteristics from diesel engines, the oxidation activity of soot particles after different thermal aging were evaluated by thermogravimetric analysis (TGA) and pyrolysis kinetics calculation, and the distribution of functional groups and elemental composition on the soot surface were investigated by FT-IR and XPS analysis. Additionally, the microstructure and graphitization degree of basic carbon with O2/NO2 aging were analyzed by HRTEM technology. The results show that the ignition temperature and activation energy of soot significantly increase after thermal aging, and their lowest values are 569 °C and 165.29 kJ mol-1 in O2/NO2/N2 atmosphere, respectively. The branching degree and content of hydrocarbon functional groups on the soot surface decrease after thermal aging, and the relative content of hydrocarbon functional groups with NO2 participating in thermal aging is the highest. The content of O element on the soot surface decreases after thermal aging, and the maximum O/C molar ratio of soot particles after thermal aging in O2/NO2/N2 atmosphere is 0.15. After thermal aging, the hybridization degree of carbon atoms and the content of -C-OH and -C[double bond, length as m-dash]O functional groups on the soot surface decrease. The content of -C-OH functional group decreases to 0.21% and 0.53% respectively after the addition of O2 and NO2 in the thermal aging atmosphere, while the content of -C[double bond, length as m-dash]O functional group increases to 4.98% and 5.98% respectively. In addition, the layer spacing and microcrystalline curvature of basic carbon particles decrease after thermal aging, however, the microcrystalline size and the graphitization degree increase.

Micro-nano morphology parameters and mechanical properties of soot particles sampled from high pressure jet flames of diesel from direct coal liquefaction

Diesel from direct coal liquefaction (DDCL) is a new type of engine alternative energy. In this study, a premixed constant volume combustion chamber system with soot particle sampling devices were built. High resolution transmission electron microscope (HR-TEM) and atomic force microscopy were applicated to characterize the micro-nano morphology parameters and mechanical properties of soot particles sampled from high pressure jet flames of DDCL. There were two in-house automatic processing codes were developed to process the HR-TEM images and extract the micro-nano morphology parameters of the soot particles. This study has systematically studied the effect of injection pressures on the micro-nano morphology parameters and mechanical properties of soot particles. The test results illustrated that there was a correlation between the micro-nano morphology parameters and mechanical properties of soot particles. Under the same combustion conditions, DDCL soot particles demonstrated smaller size, compacted structure, lower graphitization degree and weaker antioxidant capacity than that of diesel soot particles. The average adhesive force and energy dissipation of diesel soot particles were much higher, which indicated the diesel soot particles have stronger agglomeration performance. The average elastic modulus of DDCL soot particles was smaller than that of diesel, which caused the weaker ability to resist deformation for DDCL soot particles.

Activity of Catalytic Ceramic Papers to Remove Soot Particles—A Study of Different Types of Soot

Diesel soot particles are of concern for both the environment and health. To catalytically remove them, it is important to know their structure and composition. There is little described in the literature on how catalysts favor the combustion of different soot fractions. In this work, programmed temperature oxidation (TPO) experiments were carried out using Co,Ce or Co,Ba,K catalysts supported on ceramic papers. Soot particles were obtained by burning diesel fuel in a vessel (LabSoot) or by filtering exhaust gases from a turbo diesel engine in a DPF filter (BenchSoot), and compared with a commercial diesel soot: Printex U. Various characterization techniques were useful to relate the characteristics of both the soot particles and the catalysts with the TPO results. The maximum catalytic soot burn rate (TM) temperatures were in the range of diesel exhaust temperatures that would facilitate in-situ regeneration of the DPF. The Co,Ba,K catalyst showed a higher catalytic effect in LabSoot, as the latter exhibited the largest primary particles and the higher order of graphene layers, for which the potassium-containing catalyst improves the contact between soot and catalyst and favors the combustion of soot, while the Co,Ce catalyst preferentially enhanced the combustion of commercial soot by supplying active oxygen.

Impact of sulfur functional groups on physicochemical properties and oxidation reactivity of diesel soot particles

Soot particles with sulfur functional groups (SFGs) are one of the main concerns from shipping emissions, especially when they are produced from fuel combustion with high fuel sulfur content (FSC). The present study investigates the physicochemical characteristics of soot particles generated from different FSC fuels on a marine auxiliary diesel engine. A comprehensive set of experimental techniques including Fourier transform infrared (FT-IR), inductively coupled plasma optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) are employed to characterize SFGs, chemical elements, morphology, nanostructure, volatile organic fraction (VOF) content and oxidation behavior, respectively. Results reveal that, FSC has negligible influences on combustion performance, yet its high content increases the concentrations of SFGs (–SH, C–S–S, C–S, SO42−) and sulfur element VOF content and primary particle size (dp) of soot particles. Linear correlations between soot fringe length (La), oxidation activation energy (Ea) and relative concentrations of –SH and C–S are observed, respectively. Higher relative concentration of C–S bond corresponds to shorter La. The relative amounts of –SH and C–S could improve soot oxidation reactivity, associated with lower Ea. In addition, metal-sulfates are formed from the combination of SO42− with metal elements contained in fuel or lube oils, among which CaSO4 is shown an enhancing factor for soot oxidation.

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.

Variations in surface functional groups, carbon chemical state and graphitization degree during thermal deactivation of diesel soot particles

The thermal deactivation of diesel soot particles exerts a significant influence on the control strategy for the regeneration of diesel particulate filters (DPFs). This work focused on the changes in the surface functional groups, carbon chemical state, and graphitization degree during thermal treatment in an inert gas environment at intermediate temperatures of 600°C, 800°C, and 1000°C and explore the chemical species that were desorbed from the diesel soot surface during thermal treatment using a thermogravimetric analyser coupled with a gas-chromatograph mass spectrometer (TGA-GC/MS). The surface functional groups and carbon chemical state were characterized using Fourier transform infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The graphitization degree was evaluated by means of Raman spectroscopy (RS). The concentrations of aliphatic C–H, C–OH, C=O, and O–C=O groups are reduced for diesel soot and carbon black when increasing the thermal treatment temperature, while the sp2/sp3 hybridized ratio and graphitization degree enhance. These results provide comprehensive evidence of the decreased reactivity of soot samples. Among oxygenated functional groups, the percentage reduction during thermal treatment is the largest for the O–C=O groups owing to its worst thermodynamic stability. TGA-GC/MS results show that the aliphatic and aromatic chains and oxygenated species would be desorbed from the soot surface during 1000°C thermal treatment of diesel soot.

Impact of Late Post-Injection on Physicochemical Properties of Diesel Soot Particles

Impact of Late Post-Injection on Physicochemical Properties of Diesel Soot Particles

Conversion of Hazardous Diesel Soot Particles into a Novel Highly Efficient 3d Hydrogel for Solar Desalination and Wastewater Purification

Conversion of Hazardous Diesel Soot Particles into a Novel Highly Efficient 3d Hydrogel for Solar Desalination and Wastewater Purification