Catalytic oxidation for carbon-black simulating diesel particulate matter over promoted Pt/Al2O3 catalysts

Catalytic oxidation activity of carbon-black (CB) simulating the soot of diesel particulate matters to CO₂ over 3Pt/Al₂O₃, 3Pt5Mn/Al₂O₃ and 3Pt/30Ba–Al₂O₃ catalysts is investigated with model gases of diesel emission. In case of the large amount of CB compared to the amount of catalyst (3/1, w/w) in the mixture sample, insufficient oxygen at the point of sudden increase in the amount of CO₂ is leaded to the partial oxidation using the lattice oxygen of the catalyst. And the peaks of CO₂ after the first peak were attributed to the regional combustion of the CB, which was not in contact with catalyst particles. The fresh 3Pt5Mn was estimated to the oxidation states on the catalyst surface by XPS. For used sample at 700 °C, the BEs of Pt 4d5 was revealed to metallic state Pt(0) (314.4 eV) in a predominant levels compared with Pt(II) (317.3 eV). While BEs of Mn 2p were similar to that obtained from the fresh 3Pt5Mn. It is suggested that Pt is in charge of the roles in CB-oxidation, using the lattice oxygen of the catalyst. Two-stage catalytic system with the strategies of promoting the soot oxidation and NO_x reduction, simultaneously, were composed of the CB oxidation catalyst and the diesel oxidation catalyst. The catalytic oxidation of CB was accelerated by activated oxidants and exothermic reaction resulted from the diesel oxidation catalyst, which lies in upstream of two-stage. But the system with the CB oxidation catalyst sited in the upstream showed the initiation of CB oxidation at a lower temperature than the other case. Two-stage catalytic system composed of 3Pt5Mn with CB in the upstream and DOC in the downstream showed high oxidation activity with 95% consumption rate of CB to the total loaded CB in the range of 100–500 °C during the TPR process.     

Bench Scale Experiments of Diesel Soot Oxidation Using Pr0.7Sr0.2K0.1MnO3 Perovskite Type Catalyst Coated on Ceramic Foam Filters

Potassium and strontium substituted praseodymium manganate type perovskite catalyst coated on ceramic foam filters have been studied for diesel particulate removal. The synthesized catalyst coated filter pieces have been characterized by using XRD, SEM and TG analysis, whereas their catalytic activity towards soot oxidation was tested using a bench scale facility with real diesel engine exhaust. The catalyst coated filters decrease the soot oxidation T_initial value by 150 °C and T_final by 100 °C as compared to bare soot oxidation reaction, which can be considered as high activity under the actual conditions of diesel engine. The catalytic materials show good thermal stability, while their low cost will also add to their potential for practical applications. Although perovskites have been studied for laboratory evaluations of catalytic soot oxidation, present results further substantiate the possibility of using low-cost, supported, non-noble metal based catalysts for diesel exhaust emission control applications, especially for the cost-effective retrofitment of in-use vehicles with old generation engines.     

Low Cost, Ceria Promoted Perovskite Type Catalysts for Diesel Soot Oxidation

Perovskite type catalysts with SrCoO₃ and Sr_0.8Ce_0.2CoO₃ compositions have been prepared by co-precipitation and other methods and, their catalytic activity towards diesel particulate matter (PM)/carbon oxidation has been evaluated under the loose contact condition. These catalysts show excellent catalytic activity for PM/carbon oxidation, despite their low surface area and under the loose contact condition. The synergistic effects of Ce incorporation in perovskite and presence of a small amount of potassium appears to be responsible for the high soot oxidation activity of these perovskite type materials. The Ce incorporation seems to be contributing by enhancing the redox property of the catalyst, while it appears unlikely that potassium is contributing by improving the catalyst–soot contact through its volatization. The catalysts show excellent thermal stability and stable activity under repeated cycles of use.     

Characteristics of Oxidation of Diesel Paticulate Matter over a Spinel Type Cu0.95K0.05Fe2O4 Catalyst

This paper presents an experimental study on oxidation of diesel paticulate matter (PM) and aims at investigating the characteristics of PM oxidation. The experiments were performed over a Cu_0.95K_0.05Fe₂O₄ catalyst which is attributed to a spinel type metal oxide. The effects of O₂ on PM oxidation as well as on NO_x reduction were studied and the roles of O₂ in PM oxidation and in NO_x reduction, respectively, are discussed. During the temperature‐programmed oxidation of PM, SOF oxidation and soot oxidation lead to two CO₂ peaks at different temperatures. It was found that the presence of O₂ benefits PM oxidation but suppresses the reduction of NO_x into N₂ by consuming the soot. This study revealed that the appearance of PM oxidation is different from that of soot oxidation. The mechanisms on PM oxidation and NO_x reduction are discussed.     

A Novel α-Al2O3 Diesel Particulate Filter with Alkali Metal-Based Catalyst for Diesel Soot Oxidation

A diesel particulate filter (DPF) substrate was fabricated from alkali-resistant α-Al₂O₃ to make a practical use of alkali metal catalysts for diesel soot oxidation. The fundamental properties of the α-Al₂O₃-DPF, including its particle filtration efficiency, pressure drop, and thermal durability were comparable to those of the conventional DPFs. The diesel soot oxidation activity of the catalyzed α-Al₂O₃-DPF with a washcoat of alkali metal-based catalyst was, even after thermal aging, much higher than that of the conventional catalyzed-DPF with platinum group metal catalysts.     

Measurements of diesel soot oxidation kinetics in an isothermal flow reactor–catalytic effects using Pt based coatings

Despite the significant progress in soot oxidation studies, there is still high uncertainty regarding the rate expressions to model the reactions in diesel particulate filters (DPF). This uncertainty arises from inherent difficulties in sampling and measuring the reaction rate in a realistic way, as well as different properties of the examined soot. In this context, the scope of this study is the development of a novel experimental set-up capable of overcoming existing experimental difficulties. The developed set-up allows for real diesel soot oxidation studies in an isothermal flow reactor. The reaction of soot with oxygen and NO₂ is studied with synthetic gas and with real diesel exhaust and the reaction kinetics are derived for both bare and Pt-based catalyzed substrates by combining experimental and model results.     

Nanosized Pt-Perovskite Catalyst for the Regeneration of a Wall-Flow Filter for Soot Removal from Diesel Exhaust Gases

Perovskite-type catalysts have been investigated for diesel soot combustion: (i) the LaCr_0.9O_3– substoichiometric perovskite, (ii) K–La partially substituted chromites; (iii) Pt added ii-type perovskites. The catalysts prepared showed a progressively higher activity and potential for practical application in diesel particulate traps. Engine bench tests performed on a SiC wall-flow trap (Ibiden) lined with the La_0.9K_0.1Cr_0.9O_3– + 1 wt%Pt catalyst showed that the catalyst not only speeds up soot combustion on occasional trap heating (regeneration phase) but also prolongs the trap loading phase (soot accumulation during normal operation) as Pt active sites promote NO–NO₂ oxidation, followed by the non-catalytic reaction of NO₂ with the trapped soot.     

Molten Salts Are Promising Catalysts. How to Apply in Practice?

A diesel soot filter with a Cs₂SO₄V₂O₅ molten salt diesel soot oxidation catalyst has been developed. An engine test-bench was used to test it in diesel exhaust gas with ELPI analysis and to deposit diesel soot on filters for temperature programmed oxidation experiments. Molten salt (Cs₂SO₄V₂O₅) based catalytic foam has an onset temperature for catalytic oxidation of 320°C. This is a promising temperature for continuous filter-regeneration applications. Unfortunately the liquid state of the catalyst makes it unfit for the very effective wall-flow monolith filter, and necessitates the use of a foam filter as support. The onset temperature of the catalytic foam of 320°C is still too high to justify a change from wall-flow monolith to foam, as ceramic foam is a less effective filter than the wall-flow monolith. Foams are no absolute filters, and should be optimized for each application.     

Characterization of Particulate Matter from Direct Injected Gasoline Engines

The reactivity and reaction kinetics of particulate matter (PM) from direct injected gasoline (GDI) engines has been studied by O₂ and NO₂ based temperature programmed and isothermal step-response experiments, and the PM nano-structure has been characterized using HRTEM. The reactivity of the PM samples collected in filters during on-road driving was found to increase in the following order: Printex U < diesel < gasoline PI ≈ gasoline DI < ethanol for O₂ based combustion. The activation energies for O₂ and NO₂ based oxidation of PM collected from a GDI engine in an engine bench set-up was estimated to 146 and 71 kJ/mol respectively, which is comparable to corresponding values reported for diesel and model soot. Similar nano-structure features (crystallites plane dimensions, curvature and relative orientation) as observed for diesel soot were observed for gasoline PM.     

Effect of Ag, Cu, and Au Incorporation on the Diesel Soot Oxidation Behavior of SiO2: Role of Metallic Ag

The catalytic behaviors of Ag, Cu, and Au loaded fumed SiO₂ have been investigated for diesel soot oxidation. The diesel soot generated by burning pure Mexican diesel in laboratory was oxidized under air flow in presence of catalyst inside a tubular quartz reactor in between 25 and 600 °C. UV–Vis optical spectroscopy was utilized to study the electronic states of Ag, Cu, and Au(M) in M/SiO₂ catalysts. The soot oxidation was seen to be strongly enhanced by the presence of metallic silver on 3 % Ag/SiO₂ surface, probably due to the formation of atomic oxygen species during the soot oxidation process. The catalyst is very stable due to the stability of Ag⁰ species on the catalyst surface and high thermal stability of SiO₂. Obtained results reveal that though the freshly prepared 3 % Cu/SiO₂ is active for soot oxidation, it gets deactivated at high temperatures in oxidizing conditions. On the other hand, 3 % Au/SiO₂ catalyst does not present activity for diesel soot oxidation in the conventional soot oxidation temperature range. The catalytic behaviors of the supported catalyst samples have been explained considering the electron donating ability of the metals to generate atomic oxygen species at their surface.     

Advances in the Development of Filterless Soot Deposition Systems for the Continuous Removal of Diesel Particulate Matter

A model catalytic converter system has been developed to investigate and characterize novel catalyst structures for filterless diesel particulate matter deposition and oxidation in modern heavy duty vehicle diesel engine exhaust systems. The particulate traps are designed for low exhaust gas back pressures and to avoid the clogging effects observed in ceramic filters. In experiments under realistic flow conditions deposition efficiencies of up to 70% have been achieved for submicrometer particles in stacks of corrugated stainless steel foil with microsphere surface coating. The model catalytic converter system is also used to study the reaction kinetics of soot oxidation and volatilization by oxygen and nitrogen oxides under a wide range of reaction conditions, for real diesel engine soot, different model soot substances, and different types of converter surfaces.     

Simultaneous abatement of diesel soot and NOX emissions by effective catalysts at low temperature: An overview

The diesel engine generally achieves the highest fuel, energy, and thermal efficiency due to its very high compression/expansion ratio (14:1 to 25:1). Diesel engines can have a thermal efficiency that exceeds 50%. The main problem is that they emit more pollution like fine black soot particulates (C₈H to C₁₀H) and nitrogen oxides (NO_X). These pollutants have been causing serious problems for human health and the global environment and also impacts on the engine. There are many types of catalysts investigated for simultaneous control of these two pollutants, i.e., platinum group metals (PGM; Pt, Pd, Rh, and Ir) based, spinel-type oxides, hydrotalcite, rare earth metal oxides, mixed transient metal oxides, etc. The high raw material cost of PGM catalysts has become a significant issue, so developing non-PGM catalysts are one of the promising challenges. There are no extra reductants required because soot catalytically oxidizes itself in the presence of NO_X at a faster rate than molecular oxygen and simultaneously NO_X is reduced to nitrogen. The order of oxidation potential of NO_X to oxidized soot in comparison to molecular oxygen is as follows: NO₂ > NO > O₂. To meet the very strict EPA US 2010 and Euro VI regulations of particulate matter (PM) and NO_X for heavy-duty and light-duty vehicular stringent emission, it is very important to apply the integrated catalytic systems to significantly remove PM and NO_X simultaneously. Many papers related to simultaneous control of soot and NO_X over different catalysts have been published but till now some of effective catalysts showing high conversion at low temperatures (possibly within the range typical of diesel exhaust: 150–450°C) have not been reviewed. Thus, this article provides a summary of published information regarding the effective catalysts, their preparation methods, properties, and application for simultaneous control of diesel soot and NO_X.     

柴油车排气碳微粒催化燃烧研究新进展

主要介绍了国内外柴油车排气碳微粒催化燃烧的研究现状和最新进展,重点分析了贵金属、金属氧化物、金属氧化物碱金属复合型以及过渡金属复合型催化剂在去除柴油车排气中碳微粒中的特点、存在问题以及在实际中的应用,指出未来柴油车排气后处理的发展趋势是同时去除CO、HC、NOx和微粒的四元催化剂。     

Kinetics of catalyzed and non‐catalyzed soot oxidation with nitrogen dioxide under regeneration particle trap conditions

BACKGROUND: For compliance with the regulations on diesel particulate matter, car manufacturers have developed diesel particulate filters (DPF). These technologies require a regeneration method which oxidizes soot deposits in the filter. In diesel exhaust emissions there are two suitable oxidizing gases: oxygen and nitrogen dioxide. Nitrogen dioxide is much more active than O₂ and can directly attack the carbon surface. This work describes the kinetics of the oxidation of soot by NO₂ over a wide range of conditions relevant for DPF. RESULTS: The catalyzed and the non‐catalyzed oxidation of soot have been performed in a fixed‐bed reactor. The experimental results show that the overall oxidation process can be described by two additive parallel reactions: a direct C ? NO₂ reaction catalyzed by H₂O and a cooperative C ? NO₂ ? O₂ reaction catalyzed by the Pt/Al₂O₃ catalyst. The results obtained allow to propose the following kinetic law for the specific rates of the catalyzed and the non‐catalyzed oxidation of soot in the regeneration filter conditions: CONCLUSION: The kinetic parameters describing the oxidation rate of soot by NO₂ over a range of temperature and gas composition have been obtained. The extracted kinetics data are relevant for modeling the removal of trapping soot in automotive gas exhaust technology. Copyright © 2009 Society of Chemical Industry     

Potential rare-earth modified CeO2 catalysts for soot oxidation

The physico-chemical properties of ceria (CeO₂) and rare earth modified ceria (with La, Pr, Sm, Y) catalysts are studied and correlated with the soot oxidation activity with using O₂ and O₂ + NO. CeO₂ modified with La and Pr shows superior soot oxidation activity with O₂ compared with the unmodified catalyst. The improved soot oxidation activity of rare earth doped CeO₂ catalysts can be correlated to the increased meso/micro pore volume and the stabilisation of the external surface area. On the other hand, unreducible ions decrease the intrinsic soot oxidation activity of rare earth modified ceria with both O₂ and NO + O₂ due to the decreased amount of redox surface sites. The catalyst bulk oxygen storage capacity is not a critical parameter in determining the soot oxidation activity. The modification with Pr shows the best soot oxidation with both O₂ and O₂ + NO compared with all other catalysts.     

Preparation and Application of Perovskite Catalysts for Diesel Soot Emissions Control: An Overview

The diesel engines are energy efficient (1), but their particulate matter (soot) emissions are still a matter of concern even though major advances in their control are being made. For soot abatement, catalytic diesel particulate filter (DPF) technique is widely employed to trap and burn the soot. Many types of catalysts have been investigated for the soot combustion i.e. platinum group metal (PGM) based, perovskite-type oxides, spinel-type oxides, rare earth metal oxides, and mixed transient metal oxides etc. The cost of PGM catalysts is high and their availability is questionable. Further they are susceptible to poisoning and have low thermal stability. On the other hand perovskite catalysts show potential as effective soot oxidation catalyst for the DPF because of their low cost, high thermal stability and tailoring flexibility. Many papers related to soot oxidation over perovskite catalysts have been published but no review paper appears in the literature that is dedicated to soot oxidation. Thus, this article provides a summary of published information regarding pure and substituted perovskite catalyst, preparation methods, properties, and their application for diesel soot emission control.     

Ni、Pt对柴油车排气颗粒物去除催化剂的修饰作用

以改性整体式堇青石蜂窝陶瓷为载体,用Ni和Pt修饰Cu-K-V/TiO₂/γ-Al₂O₃ /cordierite催化剂,制备了用于消除柴油车排气颗粒物的催化剂;采用DSC/TG方法确定催化剂的活性及BET、TG-IR等方法对催化剂进行了表征,探讨了Ni和Pt对Cu-K-V/TiO₂/γ-Al₂O₃ /cordierite催化剂的修饰作用及老化对催化剂的影响.研究发现经Ni和Pt修饰后的催化剂能有效降低柴油车排气颗粒物的最大燃烧速率时的温度,特别是对颗粒物中最难燃烧的石墨化部分的去除;而且Ni和Pt的添加能提高颗粒物的去除效率.对含Pt催化剂,老化会降低催化剂的活性;而对含Ni的催化剂,老化使催化剂的活性增加,这可能是Ni向催化剂非孔道的外表面迁移的结果.     

Study of perovskite‐type oxides and their supported Ag derivatives for catalytic oxidation of diesel soot

A series of perovskite‐type oxides and derived Ag catalysts were prepared, and characterized by N₂‐adsorption, X‐ray diffraction and X‐ray photoelectron spectroscopy. The influences of pretreatment and Ag loading on catalytic activity for diesel soot oxidation were also investigated. Prereduction resulted in a decrease in catalytic activity. An increase in activity with Ag addition was observed, especially with more than 5% Ag loading. This catalyst could be a promising candidate for the catalytic elimination of diesel soot. © 2002 Society of Chemical Industry     

Potassium‐Activated Wire Mesh: A Stable Monolithic Catalyst for Diesel Soot Combustion

Potassium‐modified FeCrAl alloy wire mesh was developed as a catalytic diesel particulate filter to suppress the emission of soot from a diesel engine. Potassium species were deposited on wire mesh by a chemical vapor deposition method, in which a model soot was used to convert KOH into metallic K at high temperatures to subsequently activate the wire mesh. Tests showed that metallic K reacted with the enriched Al₂O₃ component on the surface derived from segregation and successive oxidation during precalcination. The resulting layer of K‐O‐Al species offers remarkable activity and stability for the catalytic oxidation of diesel soot. The K‐activated wire mesh could lower the initial temperature of soot combustion and maintain the activity for several cycles.     

Advances in the development of filterless soot deposition systems for the continuous removal of diesel particulate matter

A model catalytic converter system has been developed to investigate and characterize novel catalyst structures for filterless diesel particulate matter deposition and oxidation in modern heavy duty vehicle diesel engine exhaust systems. The particulate traps are designed for low exhaust gas back pressures and to avoid the clogging effects observed in ceramic filters. In experiments under realistic flow conditions deposition efficiencies of up to 70% have been achieved for submicrometer particles in stacks of corrugated stainless steel foil with microsphere surface coating. The model catalytic converter system is also used to study the reaction kinetics of soot oxidation and volatilization by oxygen and nitrogen oxides under a wide range of reaction conditions, for real diesel engine soot, different model soot substances, and different types of converter surfaces.