Oxidation Of Diesel Particulate Matter Research Articles

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.

Efficient simultaneous removal of diesel particulate matter and hydrocarbons from diesel exhaust gas at low temperatures over Cu–CeO2/Al2O3 coupling with dielectric barrier discharge plasma

Diesel particulate matter (DPM) and hydrocarbons (HCs) emitted from diesel engines have a negative affect on air quality and human health. Catalysts for oxidative removal of DPM and HCs are currently used universally but their low removal efficiency at low temperatures is a problem. In this study, Cu-doped CeO2 loaded on Al2O3 coupled with plasma was used to enhance low-temperature oxidation of DPM and HCs. Removals of DPM and HCs at 200 °C using the catalyst were as high as 90% with plasma but below 30% without plasma. Operando plasma diffuse reflectance infrared Fourier transform spectroscopy coupled with mass spectrometry was conducted to reveal the functional mechanism of the oxygen species in the DPM oxidation process. It was found that Cu–CeO2 can promote the formation of adsorbed oxygen ( – ) and terminal oxygen (M=O), which can react with DPM to form carbonates that are easily converted to gaseous CO2. Our results provide a practical plasma catalysis technology to obtain simultaneous removals of DPM and HCs at low temperatures.

Promotion Mechanism of CaSO4 and Au in the Plasma-Assisted Catalytic Oxidation of Diesel Particulate Matter.

Plasma-assisted catalysis has been demonstrated to be an innovative technology for eliminating diesel particulate matter (DPM) efficiently at low temperature (≤200 °C). Moreover, past studies have demonstrated that CaSO4, which exists in small concentrations (<2%) in DPM and is toxic in thermal catalytic oxidation processes, actually enhances DPM oxidation during plasma-assisted catalytic processes. However, the role CaSO4 plays in this promotion of DPM oxidation still remains unclear. The present study addresses this issue by investigating the underlying mechanisms of DPM oxidation during plasma-assisted catalytic processes using graphitic carbon as a surrogate DPM material in conjunction with CaSO4- and Au-impregnated γ-Al2O3 catalysts. The results of mass spectrometry and in situ diffuse reflectance infrared Fourier transform spectroscopy, which employs an in situ cell with a small dielectric barrier discharge space over the catalyst bed, demonstrate that CaSO4 can save and release O atoms contributing to graphite oxidation via the −S=O units of CaSO4 through a reversible surface reaction (−S=O + O → −S(−O)2). The results are employed to propose a formal mechanism of graphite oxidation catalyzed by CaSO4 and Au. These findings both improve our understanding of the plasma-assisted catalytic oxidation mechanisms of DPM and support the development of efficient plasma-assisted catalysts.

Study on oxidation activity of Ce\u2013Mn\u2013K composite oxides on diesel soot

As an effective method, diesel particulate filter (DPF) technology has a great contribution in reducing soot emissions from diesel engines. To achieve passive regeneration of DPF at low temperatures, K-doped Ce0.5Mn0.5O2 catalysts were synthesized using sol–gel method. The effect of K-doped catalysts-Kz–Ce0.5Mn0.5O2-on the oxidation of soot had been studied by thermogravimetric analysis, and the corresponding catalytic properties were evaluated based on X-ray diffraction (XRD), hydrogen temperature programmed reduction (H2-TPR), O2 temperature programmed desorption (O2-TPD) Raman spectroscopy (Raman), Brunauer–Emmett–Teller (BET) and Fourier-Transform-Infrared (FTIR).The results showed that K doping facilitated the oxidation of diesel particulate matter, which was indicated by the entire mass loss curve shifting to lower temperatures. K0.2–Ce0.5Mn0.5O2 showed the best performance among the series of K-doped catalysts. Compared with the findings for Ce0.5Mn0.5O2, the ignition temperature of soot oxidation (Ti) had been lowered by 28 ℃, and the maximum peak combustion temperature (Tm) of the dry soot decreased by 61 °C. Furthermore, compared with the Ce0.5Mn0.5O2-catalyzed reaction, K doping led to a lower activation energy and significantly improved pre-exponential factor. The minimum reaction activation energy of 27.46 kJ/mol was exhibited by K0.2–Ce0.5Mn0.5O2.

Chemical composition of diesel particulate matter and its control

ABSTRACTIn this review, we have systematically discussed diesel particulate composition and its formation, understanding of which is essential to design the effective catalyst compositions. The most commonly used after treatment strategies such as diesel oxidation catalysts, diesel particulate filters, and partial flow filters are described followed by chronological and category-wise discussions on various groups of reported soot oxidation catalysts. A detailed review is also presented on mechanistic and kinetics aspects of non-catalytic direct particulate matter (PM) or soot oxidation in air/O2 and NO2. Recent progress in catalyst development with a focus on the low-cost catalyst for diesel PM oxidation has been given more emphasis considering their renewed importance.

Catalytic oxidation of diesel particulate matter by using silver and ceria supported on alumina as the oxidation catalyst

To enable passive regeneration of a diesel particulate filter (DPF), this work seeks to study the potential of silver and ceria for the catalytic oxidation of diesel particulate matter (PM). Different contents of silver and ceria supported on alumina and silver loaded on ceria are synthesised by the incipient wetness impregnation method. The catalysts are characterised via XRD, SEM, and EDX. Catalytic PM oxidation performance for different PM/catalyst weight ratios and contact conditions is examined by using TGA. Removal of light soluble organic fraction (SOF) occurs between 110 and 350 °C through the vaporisation process. For the PM/catalyst weight ratio of 1/5, the silver compositions do not improve the depletion of light SOF but promote the combustion of both heavy SOF and soot, and the enhancement increases with silver content. For 16 wt% of silver supported on alumina, the PM/catalyst weight ratio of 1/20, and tight contact, oxidative activity is improved throughout the temperature window for light and heavy SOF and soot. The silver catalyst shows good stability for five runs. Active oxygen adspecies generated by ceria are different from those produced by silver. Enhanced performance for light SOF oxidation at a relatively low temperature is obtained using pure ceria. With the addition of alumina into ceria, light SOF removal ability of ceria is negatively affected. The positive effect on heavy SOF and soot reduction gained from the presence of silver is suppressed when ceria is mixed with silver.

Sulfur dioxide-tolerant strontium chromate for the catalytic oxidation of diesel particulate matter

A mixed oxide of strontium and chromium shows enhanced, multi-cycle catalytic oxidation performance for diesel particulate matter with sulfur dioxide tolerance.

Metal Sulfates Enhanced Plasma Oxidization of Diesel Particulate Matter

The activities for nonthermal plasma-induced oxidation of diesel particulate matter (DPM) with various metal sulfates were investigated. It was found that the metal sulfates, MgSO4, K2SO4, and CaSO4 $\cdot$ 2H2O, enhanced the energy yield of DPM oxidation while other sulfates, Na2SO4, Fe2(SO4)3, and Al2(SO4) $\cdot$ 8H2O, did not affect the energy yield. The addition of water vapor caused a promotion of DPM oxidation regardless of a metal sulfate was presented. The effect of temperature and sulfate adding amount was also investigated. The metal sulfates enhanced DPM oxidation is possibly due to the adsorption of O atoms onto the sulfates. The positive effects of H2O might be thought of as due to the formation of reactive OH radicals and the promotion of the hydrolysis of the oxygen-containing compounds on DPM surface.

A review of fundamental factors affecting diesel PM oxidation behaviors

Diesel particulate matter (DPF) is usually employed to meet the stringent regulations on particulate matter (PM) emissions for diesel engine. To resolve the DPF regeneration problem, comprehensive information about the factors influencing PM oxidation behaviors must be understood. Large amounts of factors related to PM oxidation activity have been investigated, however, some relations are still ambiguous. This paper reviews the factors related to PM oxidation activity that the factors are divided into the engine-correlated and engine-uncorrelated factors. The methods with both advantages and disadvantages to test the oxidation behaviors are introduced. The microstructure and ingredient being fundamental factors affecting PM oxidation behaviors are as the principle line to correlate PM oxidation behaviors and engine-correlated factors. The relations of engine-correlated factors with oxidation behaviors are obtained though advanced technologies that are mutual complementation. The engine-uncorrelated factors are also reviewed that these factors are vital to oxidation activity changes. Multiple-factor analysis rather than single-factor analysis should be developed to make the oxidation behaviors of diesel PM more clear.

Sustainable removal of particulate matter from diesel engine exhaust at low temperature using a plasma-catalytic method

There is a great need for a sustainable diesel particulate matter (DPM) removal approach to effectively control the emission of DPM over long term and to improve the efficiency of diesel engine. However, methods that are currently available either require a high operation temperature or an external device. Here, we report an optimized plasma-catalytic method for the sustainable removal of DPM at low temperature. Au catalyst, which was the most effective in the enhancement of DPM oxidation among the tested noble-metal catalysts, was introduced into the plasma reactor for the diesel engine test. We found that after 1.1h plasma processing, the performance of DPM removal in the condition of sole plasma (without a catalyst) was reduced due to the accumulation of precipitated DPM within the plasma reactor. As a result of an enhanced DPM oxidation efficiency due to the use of Au catalyst, the accumulation of precipitated DPM was inhibited and the performance of DPM removal was maintained until plasma was switched off (8h processing). Importantly, the maintained DPM removal caused an enriched CaSO4 deposition on the plasma-catalytic reactor, which further enhanced DPM oxidation efficiency. Thus, a sustained DPM removal performance over long term could be ensured.

Electronic state of silver in Ag/SiO2 and Ag/ZnO catalysts and its effect on diesel particulate matter oxidation: An XPS study

Diesel particulate matter (DPM) oxidation activities of 3%Ag/SiO2 and 3%Ag/ZnO catalysts were investigated. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). 3%Ag/SiO2 showed excellent activity for DPM oxidation below 300°C. The high activity is attributed to the presence of Ag0 at the surface of SiO2, which enhances the generation of superoxide O2−, the highly active species in the oxidation reactions. The activity of the catalyst did not change up to 6 oxidation cycles, indicating there is no change in electronic state of Ag during high temperature oxidation of DPM. However, 3%Ag/ZnO exhibited a very low DPM oxidation activity at the studied temperature range (25–600°C). XPS analysis performed on the catalysts before and after their use in DPM oxidation revealed that a fraction of Ag0 in the 3%Ag/ZnO converts to Ag1+ state, probably due to the electron transfer from the Fermi level of the low work function metallic Ag to the conduction band of high band gap n-type semiconductor ZnO. We demonstrate a direct relation between the DPM oxidation activity of silver and its electronic state at the catalyst surface.

Au0–Au3+ bifunctional site mediated enhanced catalytic activity of Au/ZnO composite in diesel particulate matter oxidation

Hydrogen-reduced air-calcined 1%Au/ZnO composite synthesized by gold impregnation in ZnO has been utilized as catalyst for diesel particulate matter (DPM) oxidation. The catalyst was characterized by UV-vis optical absorption, X-ray photoelectron spectroscopy and transmission electronic microscopy. The composite catalyst showed excellent activity for the oxidation of DPM at temperature as low as 230°C. The activity of the catalyst does not change up to 6 oxidation cycles. The high catalytic activity of the composite has been attributed to the formation of stable Au0–Au3+ bifunctional catalytic sites at the gold-ZnO interface, which enhances the contact efficiency of solid particulate matter on Au3+ and the generation of superoxide species on Au0. The high stability of the bifunctional Au0-Au3+ sites is associated with the electronic interactions between gold and n-type semiconductor ZnO at their interface.

Low Cost Cu/ZnO as Low Temperature (150 °C) Catalyst for Diesel Particulate Matter Oxidation

The catalytic behavior of hydrogen-reduced copper loaded ZnO, SiO2, and TiO2 has been investigated for diesel particulate matter(PM) oxidation. 5 %Cu/ZnO showed a strong diesel PM oxidation activity at 150 °C. XPS spectroscopy was utilized to study the electronic states of Cu in Cu/ZnO catalyst. Presence of Cu1+ ions at the surface of the catalyst even after its use in PM oxidation cycles was assigned responsible for its high catalytic performance. The high stability of Cu1+ is explained on basis of the isoelectronic interactions of Cu1+ (3d10) with Zn2+ (3d10) at the Cu2O–ZnO interface. Cu/SiO2 and Cu/TiO2 were not active for this reaction probably due to the absence of Cu1+ which could not be stabilized by Ti4+ or Si4+. Results indicate that 5 %Cu/ZnO catalyst can be utilized for the abatement of diesel engine emissions even from the starting point of cold engines.

Hydrogen-reduced Cu/ZnO composite as efficient reusable catalyst for diesel particulate matter oxidation

Hydrogen-reduced copper-loaded ZnO (Cu/ZnO) showed a strong diesel particulate matter oxidation activity at temperature as low as 150°C. Cu/ZnO catalyst with 5% nominal Cu content was tested for the oxidation of diesel particulate matter under air flow between 25 and 800°C. The high catalytic performance of reduced 5%Cu/ZnO even after its use in diesel particulate matter oxidation has been assigned to the presence of Cu1+ ions at its surface, determined by Auger electronic spectroscopy. The high stability of Cu1+ could be assigned to the isoelectronic interaction of Cu1+ (3d10) with Zn2+ (3d10) at the Cu2O–ZnO interface. Results presented in this work indicate that the composite catalyst can be considered as part of an exhaust catalytic system, for abating diesel particulate matter emission at low temperature.

Experimental Investigation on the Oxidation Characteristics of Diesel Particulates Relevant to DPF Regeneration

Diesel engines generally employ diesel particulate filter (DPF) systems to meet increasingly stringent emissions regulations. The development of optimum methodologies for DPF regeneration requires detailed information on the oxidation characteristics of diesel particulate matter (PM) that accumulates on the DPF under realistic engine conditions. An experimental investigation on the oxidation behavior of diesel PM collected from a DPF test system connected to the exhaust stream of a 1.9 L, 4-cylinder, light-duty diesel engine is reported. A thermogravimetric analyzer (TGA) was used to measure the instantaneous sample mass and the rate of mass loss during its oxidation for a wide range of conditions, which include initial sample mass, amount of volatile components of soluble organic fraction (SOF) in the sample, oxygen concentration, and various heat treatment schemes in both the inert and oxidizing environments. The global kinetic parameters, i.e., the reaction orders of soot and oxygen, activation energy, and pre-exponential factor, were determined for the diesel PM and surrogate soot samples. Significant differences are observed in the oxidation behavior of surrogate soot and diesel PM. The oxidation rate of surrogate soot decreases continuously as the soot is oxidized, while that of diesel soot is nearly constant until about 80% of the sample mass is oxidized, and then decreases as the sample is completely oxidized. In addition, the oxidation behavior of surrogate soot is found to be essentially independent of the heat treatment schemes used, while that of diesel soot is strongly influenced by them. These differences may be attributable to changes in soot morphology during heating/oxidation and the presence of surface functional groups and heavier SOF components in the diesel PM. The effects of SOF and thermal aging on diesel PM oxidation have also been characterized. Results indicate that the PM oxidation is only weakly influenced by the presence of volatile components of SOF, whereas it is noticeably affected by thermal aging.

Measurements of Heat Release of Diesel PM for Advanced Thermal Management Strategies for DPF Regeneration

Diesel engines typically require diesel particulate filter (DPF) systems to reduce particulate matter (PM) emissions in order to meet increasingly stringent emission regulations. While there have been noticeable advances in DPF technology, significant efforts are still needed to develop optimum DPF regeneration strategies and achieve efficient removal of diesel PM. In particular, the development of an effective thermal management system is essential to prevent the potential failure of the DPF system by the thermal runaway during soot oxidation in DPF regeneration. In an effort to develop optimum thermal management strategies, this experimental investigation is concerned primarily with measuring the instantaneous rate of heat generation as well as the total amount of heat released during the oxidation of diesel PM containing different concentrations of soluble organic fraction (SOF). The experimental approach was to measure directly, by means of a differential scanning calorimeter (DSC), the amount of heat release during the thermal reactions of diesel PM with air and to elucidate differences in the heat release characteristics of diesel PM and surrogate (model) soot. The diesel samples were collected from a cordierite particulate filter, where PM emissions bypassing the exhaust pipe of a light-duty diesel engine were deposited. Furthermore, a thermogravimetric analyzer (TGA) was used to obtain dry diesel soot samples with no volatile components present. The DSC experiments revealed that the amounts of heat released from the oxidation of SOF-containing diesel PM sample, dry diesel soot, and surrogate soot were approximately 14.67 kJ/g, 17.3 kJ/g, and 14.02 kJ/g, respectively, indicating that the largest heat release was obtained from the dry diesel soot sample. Results also indicated significant differences in the temporal rates of heat release in the oxidation of SOF-containing diesel PM, dry diesel soot, and surrogate soot. In particular, significant differences were found on the results for dry diesel soot samples with respect to the oxidation temperatures of 550°C and below 550°C in air. The heat release rate profile for the 550°C case exhibited a continuous sharp decrease after the peak value, while those for the 535°C and 525°C cases indicated first a sharp decrease, followed by slow and then sharp decrease again. The present experimental data are expected to lead to better predictive tools for thermal energy distribution during DPF regeneration, and thus the development an optimum thermal management system for DPF systems.

Mechanical Activation of Self-Propagating High-Temperature-Synthesized LaFeO3 to be Used as Catalyst for Diesel Soot Oxidation

We proposed active catalyst of SHSed LaFeO3 (LFO) as alternatives to precious metals such as platinum for promoting the oxidation of diesel particulate matter. Significantly, the LFO samples exhibited good catalytic activity for the oxidation of carbon black, though their surface area was smaller than that of Pt/Al2O3.

Electrochemical generation of active oxygen for diesel particulate matter oxidation

not Available.

Effects of O3 and NO2 on Catalytic Oxidation of Diesel PM

Abstract Oxidative activities of ten different catalysts to particulate matter (PM) emitted from a diesel engine have been compared by thermogravimetric analysis under an atmosphere containing O3 and NO2. MnO2 has been found to exceed noble metal catalysts in the PM oxidation efficiency even at 300 °C. The PM oxidative activities of transition-metal oxides possessing high formation enthalpies are enhanced by the active oxygen species owing to acceleration of redox catalytic cycles.

Investigation of Transition Metal Oxide Catalysts for Diesel PM Removal Under Plasma Discharge Conditions

Seven different transition metal oxides (TiO2, ZnO, V2O5, Fe2O3, Co3O4, MnO2, and CuO) have been investi- gated for oxidation of diesel particulate matter (PM) under plasma discharge conditions. The experiments were carried out by measuring PM oxidation rates over each catalyst using a batch-type dielectric barrier discharge reactor. It was found that TiO2, ZnO, V2O5, and Fe2O3 can promote PM oxidation, among which Fe2O3 is a most desirable catalyst for PM oxi- dative removal as PM oxidation rate promoted by Fe2O3 is highest under plasma discharge conditions. The mechanism of PM catalytic oxidation over the metal oxides has been suggested to follow the redox catalytic cycles from the correlation of the catalytic oxidation rates with the formation enthalpies per oxygen atom of the catalysts. O atoms generated by plasma discharges may play an important role in promoting the re-oxidation of the catalysts. The highest catalytic activity for the PM oxidation with Fe2O3 has been suggested to be due to the balance between the reduction rate and the re- oxidation rate within the redox catalytic cycles.