Soot Ignition Research Articles

Factors Affecting the Catalytic Performance of La-K-Mn-O Perovskite Oxides for Diesel Soot Oxidation

Abstract Soot combustion performance of K-containing perovskite oxides, La0.8K0.2MnO3 (LKM82), was evaluated under tight- and loose-contact conditions. The perovskite oxides were prepared by evaporation-to-dryness methods using malic acid or citric acid as the complexing reagents. Catalyst surface area, surface K concentration, and morphology of the LKM82 catalysts can be controlled by changing the preparation conditions. The temperature of soot combustion decreased with increasing catalyst surface area and surface K concentration of the LKM82 catalysts, indicating that these are important factors controlling the soot combustion performance. The increase in surface area and surface K concentration of the LKM82 catalysts improved soot ignition activity and promoted the soot combustion reaction after ignition. In the loose-contact mode, the ratio of the amount of catalytically combusted soot to that of non-catalytically combusted soot increased with an increase in catalyst surface area and surface K concentration of the LKM82 catalysts. The apparent activation energy of the catalytic soot combustion with the perovskite oxides that have both high surface area and high surface K concentration was much lower than that of non-catalytic soot combustion.

The role of crystallite size of iron oxide catalyst for soot combustion

A series hematite structure iron oxide nanoparticles of various sizes was synthesized and tested in the soot combustion in oxygen rich conditions in the tight and loose contact modes. The catalysts were characterized by XRD, TEM, and Raman Spectroscopy, whereas the catalytic reactivity with model soot (Printex U) was evaluated by TGA/DTA method. It was found that the catalysts activity is size dependent for the particles dimensions in the range of 5–100nm with the smallest one exhibiting the highest activity (lowest soot ignition temperature). The most active nanohematite particles, formed in situ in the laboratory and real process conditions of light fuel oil combustion with addition of fuel borne catalyst (FBC) precursors, exhibit the beneficial size range of 5–15nm.

Influence of an iron-based fuel-borne catalyst on physicochemical and toxicological characteristics of particulate emissions from a diesel engine

Metal-based fuel-borne catalysts (FBCs) have been used with diesel fuels to effectively reduce soot and diesel particulate matter (DPM) emissions from both on-road and off-road applications. However, there is a lack of detailed investigations on the potential changes in the properties of particulates, when FBCs-doped fuels are combusted in diesel engines. This study fully evaluates the potential impacts of ferrocene-doped ultralow sulfur diesel (ULSD) fuels on physical, chemical and toxicological characteristics of the particulates emitted by a single cylinder, direct-injection diesel engine working at a constant speed and at three engine loads. The results indicated that ferrocene-doped fuels could effectively reduce the particulate mass and elemental carbon (EC) emissions, while increasing the proportion of both organic carbon (OC) and water-soluble organic carbon (WSOC) in particles. Particle-phase PAHs and n-alkanes emissions increased with an increase of Fe in the fuels. Ferrocene addition also led to lower soot ignition temperature and activation energy. However, the total number emissions of particles from ferrocene-doped fuels dramatically increased due to the formation of Fe-rich nuclei mode particles. Compared to pure ULSD, the particles emitted from ferrocene-doped fuels showed a slight decline in cell viability. The Fe in the particles and the changes in chemical composition of particulates are thought to be responsible for the variation of cell viability.

Nanostructured platinum catalyst coating on diesel particulate filter with a low-cost electroless deposition approach

To meet an increasingly stringent regulation in suppression of particulate matter (PM) in exhaust stream, catalytic diesel particulate filter (cDPF) is a promising solution that catalytically converts carbon agglomerate to gaseous emissions, releasing to atmosphere without particular caution. A low-cost electroless coating approach is presented here to realize in situ growth of nanostructured metal crystals inside micropores without the need of electrical contacts and regardless of the substrate’s chemical property. SEM and X-ray spectroscopy (EDX) showed that silver (Ag) precursor gives rise to well-dispersed Pt particles on the multi-walled support with low aggregation and high surface density. Catalytic performance on this metallized filter is quantitatively weighed by thermal gravity analysis (TGA), which exhibits the drastic difference between bare soot and presence of Pt nanoparticles. In addition, the participation of NOx significantly reduced the soot ignition temperature, provided that involving of oxidase gas triggers the distinct pathway of catalytic reaction. Overall, the developed protocol paves a new avenue for chemically embedding nanostructured Pt catalysts in micrometric hollow reactors, producing a large-scale catalytic surfaces for soot combustion and well-balancing the economic and technical needs.

Effect of oxygenated fuels on physicochemical and toxicological characteristics of diesel particulate emissions.

A systematic study was conducted to make a comparative evaluation of the effects of blending five different oxygenates (diglyme (DGM), palm oil methyl ester (PME), dimethyl carbonate (DMC), diethyl adipate (DEA), and butanol (Bu)) with ultralow sulfur diesel (ULSD) at 2% and 4% oxygen levels on physicochemical and toxicological characteristics of particulate emissions from a nonroad diesel engine. All blended fuels led to an overall decrease in the particulate mass concentration and elemental carbon (EC) emissions, which was strongly associated with the oxygen content in fuels and the specific type of fuels used. In general, the proportion of particulate-bound organic carbon (OC) and water-soluble organic carbon (WSOC) increased while using oxygenated fuel blends. Compared to ULSD, all fuel blends showed different emission factors of particle-phase PAHs and n-alkanes, slight alterations in soot nanostructure, lower soot ignition temperature, and lower activation energy. The total counts of particles (≤ 560 nm diameter) emitted decreased gradually for ULSD blended with DMC, DEA, and Bu, while they increased significantly for other fuel blends. The in vitro toxicity of particulates significantly increased with ULSD blended with DMC and DEA, while it decreased when ULSD was blended with PME, DGM, and Bu.

Catalytic DPF microwave assisted active regeneration

In the last decades, diesel engines have attracted an increasing interest from vehicles producer and public, due to their higher thermal efficiency, less CO and unburned hydrocarbons emission, and longer lifetime comparing with gasoline engines. However, the high emission of soot particulates and NOx are still their key problems. The combination of filters and oxidation catalysts is one of the most effective after-treatment techniques to eliminate soot particles from the exhaust gases: the deposited catalyst lowers the soot ignition temperature from 550°C (uncatalyzed reaction) to the typical values of diesel exhaust gases (180–400°C).In our previous works we showed that the simultaneous use of a microwave (MW) applicator and a specifically catalyzed Diesel Particulate Filter (DPF), loaded up to 20wt% of Copper Ferrite (CuFe2O4), allows to reduce the temperature, the energy and the time required for the regeneration. Starting by these very promising results, in this work we continued to study in order to further improve the performances of the catalyzed DPF, reducing the temperature and minimizing the MW energy required for the regeneration. Furthermore we verified the feasibility of the MW technology by assessing the energy balance of the regeneration phase, comparing it to the actually employed regeneration technologies.

Enhanced soot combustion over partially substituted hydrotalcite-drived mixed oxide catalysts CoMgAlLaO

A series of hydrotalcite-derived multicomponent oxide catalysts Co2.5Mg0.5Al1–x%Lax%O (denoted as CMALax, x=0, 5, 8, 10 or 15) with different La contents were synthesized by co-precipitation, and employed for catalytic soot combustion and NOx storage at lean condition. It is found that the La-substituted catalysts are more active than the one without La for soot combustion and NOx storage. Among all the catalysts CMALax, CMALa10 (x=10) exhibits the highest catalytic performance, showing the largest NOx storage capacity (300μmol/g) and the lowest temperature for the maximal soot oxidation rate (Tm=388°C). The results of H2-TPR and O2-TPD indicate that the La-substitution can enhance the redox properties and increase the amount of surface lattice oxygen species of the catalysts. The results of soot combustion kinetics show that the apparent activation energy of CMALa10 is the lowest (92.75kJ/mol). Based upon the catalytic performance and in situ DRIFTS characterization, a nitrate and/or NO2 enhanced soot combustion mechanism over CMALa10 was proposed. It is revealed that at low temperature the stored nitrate can directly promote soot ignition, while at high temperature the NO2 species arising from NO oxidation or nitrate decomposition act as the main active species for soot combustion.

Investigation of the effect of biodiesel blends on the performance of a fuel additive-assisted diesel filter system

The results of full-scale regeneration tests with a unit silicon carbide diesel particulate filter installed on a single-cylinder diesel engine are presented. Two sets of transient regeneration experiments, one for each fuel used, with high level of exhaust gas flow rate (normalized per filter volume) and markedly different levels of soot loading were performed. The test fuels were conventional diesel (denoted as B0) and B20 biodiesel blend. The effect of the biodiesel on filter regeneration was further investigated by means of infrared thermography. The main objective was to investigate the catalytic soot ignition and regeneration propagation when the engine is fueled by biodiesel blends. Special focus was on the temperature distribution across the filter channels and the evolution of the regeneration at the central and peripheral part of the filter. The results indicated a faster evolution of the regeneration with lower overall filter wall temperatures with favorable effects on the filter durability, when the engine is fueled by B20.

Physicochemical and toxicological characteristics of particulate matter emitted from a non-road diesel engine: Comparative evaluation of biodiesel-diesel and butanol-diesel blends

Combustion experiments were conducted to evaluate the effects of using blends of ultralow sulfur diesel (ULSD) with biodiesel or n-butanol on physicochemical and toxicological characteristics of particulate emissions from a non-road diesel engine. The results indicated that compared to ULSD, both the blended fuels could effectively reduce the particulate mass and elemental carbon emissions, with butanol being more effective than biodiesel. The proportion of organic carbon and volatile organic compounds in particles increased for both blended fuels. However, biodiesel blended fuels showed lower total particle-phase polycyclic aromatic hydrocarbons (PAHs) emissions. The total number emissions of particles ≤560nm in diameter decreased gradually for the butanol blended fuels, but increased significantly for the biodiesel blended fuels. Both the blended fuels indicated lower soot ignition temperature and activation energy. All the particle extracts showed a decline in cell viability with the increased dose. However, the change in cell viability among test fuels is not statistically significant different with the exception of DB-4 (biodiesel–diesel blend containing 4% oxygen) used at 75% engine load.

Effects of B20 on the Operation of a Single-Cylinder Engine Equipped with a SiC Diesel Particulate Filter

This is an experimental and computational study of the effect of a low-percentage biodiesel blend on the operation, diesel filter loading, and fuel additive-assisted regeneration behavior on a conventional, direct injection (DI), single-cylinder diesel engine. The evolution of regeneration was studied by means of infrared thermography on the unit filter. The results of two sets of regeneration experiments, one for each fuel blend, with high-space velocity levels are discussed. The test fuels were conventional diesel (denoted as B0) and B20 biodiesel blend. The objective was to investigate the differences in catalytic soot ignition and regeneration propagation when the engine is fueled by biodiesel blend. The investigation is assisted by the application of an in-house diesel particulate filter (DPF) regeneration modeling tool. The results indicate a faster evolution of the regeneration with B20 fuel, with lower overall filter wall temperatures prevailing, more favorable on filter durability grounds.

Influence of Potassium and NO Addition on Catalytic Activity in Soot Combustion and Surface Properties of Iron and Manganese Spinels

Two series of (0–4 wt%) potassium doped oxide catalysts based on iron and manganese spinel were prepared. The synthesized materials were characterized in terms of their structure (XRD, Raman spectroscopy) and surface electronic properties (work function measurements). The catalytic activity towards soot combustion was determined by temperature programmed oxidation of a physical mixture of soot and catalyst in tight contact in gas oxygen mixtures with and without NO addition. For iron spinel based materials, where potassium is localized at the surface, the catalytic activity correlates with the work function lowering upon K doping, while for manganese spinel based materials, where potassium is incorporated into the bulk (formation of KMn4O8 or KMn8O16), the correlation was not found. The presence of NO in the gas mixture leads to a systematic decrease of soot ignition temperature for all samples.

The effect of Ca2+ and Al3+ additions on the stability of potassium disilicate glass as a soot oxidation catalyst

Potassium disilicate (K2Si2O5) glasses substituted with additions of Ca2+ and Al3+ have been prepared, characterized and tested as diesel soot oxidation catalysts. Ca and Al modify the silicate glass network, resulting in improved stability for catalyzing oxidation of diesel soot. TGA and water immersion studies showed that substituting K2O with CaO can improve the chemical stability with a small loss of catalytic activity. (K2O)0.5(CaO)0.5(SiO2)2 had a soot ignition temperature (Tig) around 410°C and also excellent catalytic stability with repeated soot oxidation cycling. Similarly, substituting with Al3+ gave improved stability, with (K2O)0.7(Al2O3)0.3(SiO2)2 exhibiting a Tig around 370°C and better stability than K2O·2Si2O2. The activity results are interpreted with insights gained from FTIR characterization.

Soot combustion improvement in diesel particulate filters catalyzed with ceria nanofibers

Ceria nanofibers were prepared and deposited on SiC diesel particulate filters (DPFs), aiming at improving the soot-catalyst contact conditions and promote soot combustion at lower temperatures than in the noncatalytic case. In particular, the nanofibers have been found to be very active with respect to other ceria catalyst morphologies, due to their arrangement in a network which enhances the number of soot-fiber contact points.This effect was initially elucidated in a series of tests of soot temperature programmed combustion, which were carried out on the catalysts powders mixed with soot in loose contact conditions: a specific sub-set of nanofibers exhibited a 112°C anticipation of the onset oxidation temperature (10% of total soot combustion) with respect to the non-catalytic test, and 38°C with respect to ceria nanopowders obtained with the so-called Solution Combustion Synthesis (SCS).The nanofibers were then supported on Alumina washcoated DPFs, which were loaded with soot for 1h, and subsequently subjected to a progressive temperature increase to induce soot ignition. Both CO2 concentration in the outlet gas, and the pressure drop, were recorded during these tests. The main advantage given by the nanofiber catalyzed DPF, with respect to the other investigated morphologies, was not related to the maximum rate of soot oxidation, which was similar for all ceria catalysts, but again to the onset temperature. In fact, the pressure drop curve started to decrease more than 50°C before the DPF catalyzed with ceria through in situ SCS.This behavior could greatly improve the soot oxidation activity especially for DPF passive regeneration purposes.

In situ investigation of Diesel soot combustion over an AgMnOx catalyst

An AgMnOx catalyst (3.5wt.% Ag) incorporating silver ions in a Mn2O3 phase exhibits high performances for soot oxidation below 300°C. Its structural and redox properties have been investigated under reaction conditions using in situ XRD and DTA-TGA measurements. The catalyst appears unmodified during soot combustion experiments under oxygen, but in the absence of oxygen the soot is stoichiometrically oxidised by lattice oxygen leading to catalyst bulk reduction according to the steps Mn2O3→Mn3O4→MnO.The isotopic reaction product composition (C16O2, C18O16O, C16O2, C16O and C18O) obtained during soot combustion experiments under 18O2 reveals that the reaction follows a redox mechanism, in which the transfer of lattice oxygen from the catalyst to the soot is responsible for the soot ignition at low temperature.

NOx-Assisted Soot Oxidation on Pt–Mg/Al2O3 Catalysts: Magnesium Precursor, Pt Particle Size, and Pt–Mg Interaction

Pt–Mg/Al2O3 soot oxidation catalysts were prepared by impregnating either magnesium acetate or magnesium nitrate on alumina-supported platinum catalyst. The influence of Mg addition on the structure and catalytic behaviors of Pt/Al2O3 catalysts were investigated by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) analysis, transmission electron microscopy (TEM), H2 chemisorption, thermogravimetric (TG) analysis, Fourier transform infrared spectroscopy (FTIR), NOx temperature-programmed desorption (NOx-TPD), NO temperature-programmed oxidation (NO-TPO), and soot temperature-programmed oxidation (soot-TPO). In spite of the coverage of surface Pt by magnesium species and the weakened oxidation resistance of Pt, the Pt–Mg/Al2O3 catalyst derived from magnesium acetate exhibits a higher soot oxidation activity than that prepared with magnesium nitrate, which is mainly determined by the larger Pt particle size on this catalyst. Additionally, the synergistic effect between Pt and Mg enhances the NO oxidation activity and NOx storage capacity of Pt–Mg/Al2O3 catalyst. More NO2 is produced in the temperature range of soot oxidation on this catalyst than on the Mg-free Pt/Al2O3 catalyst with a similar Pt particle size, which efficiently promotes the ignition of soot.

Sr 1− xK xTiO 3 catalysts for diesel soot combustion

Strontium titanates partially substituted with potassium (Sr 1− x K x TiO 3, x = 0.1–0.5) were prepared by sol–gel citric method. The obtained materials were characterized by XRD, S BET and cyclohexanol (CHOL) decomposition measurements, their catalytic activity in soot combustion was determined. It has been shown that substitution of strontium by potassium lowers temperature of soot ignition temperature by 270 °C in a 10% O 2 in Ar atmosphere and ca 400 °C in a 1500 ppm of NO 2, 10% O 2 in Ar atmosphere for Sr 0.2K 0.2TiO 3. The potassium promoting effect is discussed in terms of surface basicity and creation of oxygen vacancies where molecular oxygen or (NO, NO 2) is adsorbed forming basic surface oxygen species active for soot oxidation.

Determination of active site densities and mechanisms for soot combustion with O 2 on Fe-doped CeO 2 mixed oxides

Fe-doped CeO 2 mixed oxides were studied for soot combustion with O 2 under tight contact conditions. They show increased activity compared to that of pure CeO 2 and Fe 2O 3. The optimum Fe content according to soot ignition temperatures is Fe/(Ce + Fe) = 10 at.%. However, on the basis of turnover frequencies, the samples with a Fe/(Ce + Fe) ratio between 5 and 20 at.% show similar activity. Characterization of the catalysts and a kinetic study show that the reaction proceeds via a redox mechanism. The active sites were determined to be composed of Fe–O–Ce species, and the active oxygen was quantified using isothermal anaerobic titrations with soot as a probe molecule. The redox property for the Fe–O–Ce species is much stronger than for the Ce–O–Ce species. The methodology for quantifying active redox sites can be extended to soot combustion on all similar oxide systems.

Simultaneous soot combustion and nitrogen oxides storage on potassium-promoted hydrotalcite-based CoMgAlO catalysts

A series of potassium-promoted hydrotalcite-based CoMgAlO mixed oxide catalysts used for simultaneous soot combustion and nitrogen oxides storage were prepared by impregnation method. The techniques of TG/DTA, XRD, H 2-TPR and in situ DRIFTS were employed for catalyst characterization. Over the catalyst containing 7.5% or 10% K, the soot ignition temperature ( T i = 260 °C) and total removal temperature ( T f = 390 °C) are decreased by 180 °C and 273 °C, respectively, as compared with the uncatalyzed reaction. The results of kinetic calculation show that the presence of K-promoted catalysts decreases the activation energy of soot combustion from 207 kJ/mol to about 160 kJ/mol. When 400 ppm NO is introduced, lower characteristic temperatures or higher reaction rate for soot oxidation is achieved. Simultaneously, relatively larger nitrogen oxides storage capacity is obtained. It is revealed by H 2-TPR that the addition of K increases the amount of active Co sites and the mobility of bulk lattice oxygen due to the low melting point of K-containing compounds, the low valence of K + and the strong interaction between K and Mg(Al). For nitrogen oxides storage, different routes via chelating bidentate nitrates, monodentate nitrates and ionic nitrates are confirmed by in situ DRIFTS over the CoMgAlO catalysts with potassium loadings of 0, 1.5 and 7.5%, respectively.

Preparation, characterization, catalytic activity and CO2 absorption/desorption studies of Ln/K (Ln = La, Sm, Y) catalysts for diesel soot elimination

Ln/K oxide catalysts (Ln=La, Sm, Y) supported on the alumina substrate have been prepared and their catalytic activities of diesel soot oxidation were tested by TPR system. The results showed that all La/K, Sm/K and Y/K catalysts showed a similar change of catalytic activity with the variation of K content. Nevertheless, Y/K catalyst was more active for diesel soot oxidation with a soot ignition temperature of about 350°C at a loose soot/catalyst contact mode. XRD, TG/DSC analyses were employed to investigate the structures and thermal behaviors of catalysts. It was found that the oxides would react with KNO3 to form the solid solution and the K+ saturation level was related to the ionic radii of the Ln3+. The Ln/K catalysts showed a physical CO2 absorption ability that was further enhanced at higher temperature. However, when the temperature was above a critical temperature, the absorption ability was reduced. The CO2 absorption characteristics was believed to be diffusion controlled and was attributable to the lattice defects (oxygen vacancies) caused by the solid solution formation. The dynamic CO2 transportation within the catalyst could play an important role on the catalytic oxidation process.

Soot combustion activity of NO -sorbing Cs–MnO –CeO2 catalysts

Abstract Activities of Cs-loaded MnOx–CeO2 for combustion of model diesel soot (carbon black) and sorptive NO uptake have been studied. MnOx–CeO2 is a pseudo-solid solution having redox properties favorable for soot oxidation. The addition of Cs not only lowered the temperature of soot ignition (Ti), but also increased oxidative NOx adsorption to form nitrate on the surface. Soot ignition over Cs–MnOx–CeO2 was further promoted in a stream of NO/O2, presumably because nitrate on the surface plays a role of an oxidizing agent. Soot ignition started just before sharp desorption of NOx, suggesting that adsorbed nitrate species would directly interact with soot.