Catalytic Combustion Of Diesel Soot Research Articles

One step citric acid-assisted synthesis of Mn-Ce mixed oxides and their application to diesel soot combustion

Mn-Ce catalysts were prepared by a one-step synthesis method using citric acid, and were characterized by X-ray diffraction, CO temperature-programmed reduction, laser Raman spectroscopy and X-ray photoelectron spectroscopy. These catalysts were applied to the catalytic combustion of diesel soot in the presence of nitric oxide. A remarkable influence of the ratio of precursors and the method of synthesis on the physicochemical properties and subsequent catalytic activity was evidenced. The mixed oxides had higher activities than the individual ones, showing a synergistic effect whereby the catalyst with Mn/(Mn + Ce) = 0.1 had the lowest temperature of the maximum combustion rate.Mechanical mixtures of oxides were also prepared in order to better understand the synergistic effect observed. The main TPO peak was located at a similar temperature for both methods of synthesis. However, the TPO profiles of the catalysts synthesized by mechanical mixing had a shoulder at around 420 °C, which was more evident for catalysts prepared with lower Mn contents. This fact could be related to the coexistence of different MnOx species, as demonstrated by XRD, which exhibited different catalytic performances on oxidation reactions. The formation of a solid solution between Mn and Ce oxides for a ratio of Mn/(Mn + Ce) < 0.25 was observed, which enhanced the Ce4+ ↔ Ce3+ redox process. It was observed that both the coexistence of Mn2O3 and Mn3O4 at high concentrations and the formation of a solid solution strongly favored the oxidation of diesel soot, obtaining lower values of maximum combustion rate temperature.

Investigation into the Anticoking Performances of Sol–Gel-Derived SiO2 and SiO2–CeO2 Coatings during Thermal Pyrolysis of Light Naphtha

CeO2-based materials are widely applied in a three-way catalyst framework for catalytic combustion of diesel soot. For the application of CeO2 in coking inhibition during thermal cracking of hydroc...

Catalytic Combustion of Diesel Soot on Ce/Zr Series Catalysts Prepared by Sol-Gel Method

Cerium-zirconium (Ce-Zr) solid solutions have been extensively used in a wide variety of catalytic processes due to their unique catalytic features in conjunction with lower cost compared to noble metal-based systems. A series of Ce-Zr-based catalysts was prepared by the sol-gel method. The structure and morphology of these catalysts were characterized by X-ray diffraction, thermogravimetric-differential scanning calorimetry, scanning electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy. Furthermore, investigation on catalytic performance was carried out by constructing a test platform, and the result indicated that the catalysts apparently decreased the soot ignition temperature. These catalysts exhibited higher catalytic activity for soot oxidation under narrow contact conditions. The results revealed that some soot particles could react with adsorbed oxygen, and other part of diesel soot reacted with lattice oxygen. The activity of these catalysts was attributed to synergistic effect arising from the combination of K/Co/Zr and Ce-Zr solid solution, which led to the decrease in the ignition temperature to 294 °C (data from the test platform). The catalyst still keeps good stability and catalytic activity after the cycle oxidation experiment. A reaction pathway was proposed to explain catalytic combustion process of soot, i.e., combination of K/Co/Zr with Ce-Zr solid solution reduced the binding energy of Ce-Zr solid solution, which was conducive to provide more active sites to release the active oxygen (O2−) or lattice oxygen (O2−).

Application of Mn-Based Catalysts for the Catalytic Combustion of Diesel Soot

Application of Mn-Based Catalysts for the Catalytic Combustion of Diesel Soot

Novel ceramic paper structures for diesel exhaust purification.

The catalytic combustion of diesel soot is addressed with flexible and structured "paper catalysts". Two different series of catalysts were prepared either by drip impregnation or by a spray method to deposit a mixture of Co, Ba, and K or a mixture of Co and Ce onto SiO2-Al2O3 ceramic paper matrixes. In every case, CeO2 nanoparticles were added to bind the ceramic fibers. SEM images showed that the impregnation method generated catalytic particles concentrated as large chunks (> 10μm), mainly at ceramic fiber crossings, whereas the spray method produced smaller catalytic particles (< 1μm) well distributed throughout the ceramic paper. Besides, Co-Ba-K particles appeared better dispersed on the surface of ceramic fibers than Co-Ce due to the presence of K. Additionally, FTIR spectra showed the formation of O22- and O2- species associated with CeO2 (binder) on the samples containing potassium which gave the Co-Ba-K-ceramic paper good catalytic properties, thus making the Co-Ba-K drop impregnated the best catalyst both considering activity and stability. Successive temperature programmed oxidation (TPO) runs up to 700°C caused the formation of cobalt silicates in the catalytic ceramic paper prepared by the spray method, as indicated by TPR. The formation of these species was probably favored by the smaller size of cobalt particulates and their higher dispersion in the catalysts prepared by the spray method. This provoked the partial loss of the redox properties of Co3O4. TPR experiments also indicated the formation of BaCoO3 in Ba-containing ceramic paper, which could help in maintaining the catalyst activity after several TPO runs through the capacity of this mixed perovskite-type oxide to trap and release NOx.

Catalytic combustion of diesel soot over Fe and Ag-doped manganese oxides: role of heteroatoms in the catalytic performances

Fe/Ag-doped manganese oxides show promising catalytic activities in diesel soot combustion, which occurviamechanisms involving activated surface/lattice oxygen species.

A highly effective catalyst of Co-CeO2 for the oxidation of diesel soot: The excellent NO oxidation activity and NOx storage capacity

In the catalytic combustion of diesel soot, the role of NO in the exhaust emission and the simultaneous reduction of NO by soot are two fascinating problems. Herein, the Co-CeO2 catalyst prepared by the citrate acid sol-gel method was developed to catalyze the NOx-assisted soot oxidation. The effect of the Co amount on the physicochemical and catalytic properties of the Co-CeO2 catalysts was investigated in detail. When the molar ratio of Co/Ce was 50/50, the Co50Ce50 mixed oxide catalyst exhibited the lowest soot oxidation temperature (Tm of 335°C) in the feed gas of NO+O2, and the presence of water can improve obviously the catalytic combustion of soot with Tm of 310°C. The presence of Co can improve the reduction of surface oxygen of ceria, and Ce can promote the reduction of Co3O4 to CoO, resulting in the enhancement of the catalytic activity of Co-CeO2 for NO oxidation and its capacity for NO2 storage as the surface nitrates. The soot oxidation on the Co-CeO2 catalyst can be promoted by “NO2-assistance”: the nitrate species are preferentially formed on the Co active sites and stored on the catalyst surface, and then NO2 produced by NO oxidation and the decomposition of nitrate stored on the surface at lower temperature, reacts with soot. That is, the stored NOx species initiates the beginning of soot oxidation, and the NO oxidation ability of the catalyst is responsible for the extensive soot oxidation by NO+O2, in which NO is reduced by carbon in soot combustion. The combination of high NO oxidation activity and high NO2 storage capacity makes the Co50Ce50 oxide catalyst as an efficient catalyst for the NOx-assisted soot oxidation.

Atomic layer deposition of cerium oxide for potential use in diesel soot combustion

The particulate soot emission from diesel motors has a severe impact on the environment and people's health. The use of catalytic convertors is one of the ways to minimize the emission and decrease the hazard level. In this paper, the activity of cerium oxide for catalytic combustion of diesel soot was studied. Thin films of cerium dioxide were synthesized by atomic layer deposition using tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato)cerium [Ce(thd)4] and ozone as precursors. The characteristics of the films were studied as a function of deposition conditions within the reaction temperature range of 180–350 °C. Thickness, crystallinity, elemental composition, and morphology of the CeO2 films deposited on Si (100) were characterized by ellipsometry, x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, and field emission scanning electron microscopy, respectively. The growth rate of CeO2 was observed to be 0.30 Å/cycle at temperatures up to 250 °C with a slight increase to 0.37 Å/cycle at 300 °C. The effect of CeO2 films grown on stainless steel foil supports on soot combustion was measured with annealing tests. Based on the analysis of these, in catalytic applications, CeO2 has been shown to be effective in lowering the soot combustion temperature from 600 °C for the uncoated substrates to 370 °C for the CeO2 coated ones. It was found that the higher deposition temperatures had a positive effect on the catalyst performance.

Oxidation of diesel soot on binary oxide CuCr(Co)-based monoliths

Binary oxide systems (CuCr2O4, CuCo2O4), deposited onto cordierite monoliths of honeycomb structure with a second support (finely dispersed Al2O3), were prepared as filters for catalytic combustion of diesel soot using internal combustion engine's gas exhausts (O2, NOx, H2O, CO2) and O3 as oxidizing agents. It is shown that the second support increases soot capacity of aforementioned filters, and causes dispersion of the particles of spinel phases as active components enhancing thereby catalyst activity and selectivity of soot combustion to CO2. Oxidants used can be arranged with reference to decreasing their activity in a following series: O3≫NO2>H2O>NO>O2>CO2. Ozone proved to be the most efficient oxidizing agent: the diesel soot combustion by O3 occurs intensively (in the presence of copper chromite based catalyst) even at closing to ambient temperatures. Results obtained give a basis for the conclusion that using a catalytic coating on soot filters in the form of aforementioned binary oxide systems and ozone as the initiator of the oxidation processes is a promising approach in solving the problem of comprehensive purification of automotive exhaust gases at relatively low temperatures, known as the “cold start” problem.

Influence of MnO&lt;SUB&gt;x&lt;/SUB&gt; Loading on Activity of MnO&lt;SUB&gt;x&lt;/SUB&gt;/Ce&lt;SUB&gt;0.7&lt;/SUB&gt;Zr&lt;SUB&gt;0.2&lt;/SUB&gt;La&lt;SUB&gt;0.1&lt;/SUB&gt;O&lt;SUB&gt;2&lt;/SUB&gt;-Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt; Catalyst for Catalytic Combustion of Diesel Soot

Influence of MnO&lt;SUB&gt;x&lt;/SUB&gt; Loading on Activity of MnO&lt;SUB&gt;x&lt;/SUB&gt;/Ce&lt;SUB&gt;0.7&lt;/SUB&gt;Zr&lt;SUB&gt;0.2&lt;/SUB&gt;La&lt;SUB&gt;0.1&lt;/SUB&gt;O&lt;SUB&gt;2&lt;/SUB&gt;-Al&lt;SUB&gt;2&lt;/SUB&gt;O&lt;SUB&gt;3&lt;/SUB&gt; Catalyst for Catalytic Combustion of Diesel Soot

Catalytic combustion of diesel soot over perovskite-type catalyst: Potassium titanates

Potassium titanates with a high crystallinity were successfully prepared by the sol-gel method and characterized by XRD, SEM, and BET surface area measurements. K6Ti4O11, K2Ti2O5, K2Ti4O9 were found to have better soot oxidation performance compared with Pt/TiO2 and CeO2 based catalysts. K2Ti2O5 may be an excellent candidate for soot oxidation due to its high oxidation activity, water-stability, resistance to sulfur poisoning and economical advantages. Certain amount of NOx can contribute to the catalytic combustion of diesel over potassium titanates, implying that K2TiO5 may be a kind of catalyst for simultaneous removal of NOx and soot.

Diesel particulate matter combustion with CeO 2 as catalyst. Part I: System characterization and reaction mechanism

In this work, a reaction mechanism for the catalytic combustion of diesel soot on cerium oxide is proposed. Kinetic results and catalyst characterization by Fourier-transformed Infra-Red spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), X-ray Diffraction Spectroscopy (XRD), and high frequency CO 2 pulses are used to obtain such mechanism. Temperature-programmed-oxidation experiments carried out up to intermediate temperatures made it possible to detect a transient kinetic response, in which a maximum in reaction rate at constant temperature was observed. This behavior is explained taking into account the amount of peroxides formed on the ceria surface. As the calcination temperature increases (from 400 to 800 °C), the amount of cerium superoxide and peroxide increases, thus accelerating the soot combustion reaction. These compounds were detected by FTIR. A higher total oxygen concentration on the ceria surface was detected by XPS on the catalyst calcined at high temperature. Carbon dioxide is not adsorbed on this support. The proposed reaction mechanism involves the formation of superoxides and peroxides. The latter are the active species that react with soot. These steps are strongly affected by temperature, being it possible to explain the kinetic results with this mechanism.

Introduction to the Catalytic Combustion of Diesel Soot

The heterogeneous catalytic reaction containing solid particle as reactant is a class of important and complex chemical reaction. The solid particles such as soot emitted from diesel engines, are becoming increasingly important in the context of cleaning air and lowering automotive emissions. Diesel soot particulates are defined by the US Environmental Protection Agency (EPA) as “all compound collected on a pre-condition filter in diluted diesel exhaust gases at a maximum temperature of 50°C”. The catalytic combustion is considered as one of effective method for purifying these diesel soot pollutants. Supported oxide catalysts were originally developed for the catalytic combustion, but they are not especially active at low temperatures (<400°C) under the loose contact condition between catalysts and soot [1,2]. Noble metal catalysts such as platinum and gold, on the other hand, are efficient and exhibits high activity [3,4]. However, Pt is very expensive and causes the great emissions of sulfates. Thus, the development of active and stable catalysts without noble metals for the catalytic combustion of soot particles at low-temperature remains a significant challenge.

High-throughput approach to the catalytic combustion of diesel soot II: Screening of oxide-based catalysts

Following the development of a high-throughput (HT) methodology for the evaluation of diesel soot oxidation catalysts in a 16 parallel channels reactor, a library of over 60 catalysts was tested under optimized conditions. The catalyst compositions were chosen to include solids which specific properties like oxygen storage capacity, oxygen mobility and ionic conductivity. The key parameters for high activity appear related to the presence of active and mobile surface oxygen species, and to an appropriate catalyst particle size in order to favour the number of contacts with the soot. In contrast, high oxygen storage capacity and bulk oxygen ion mobility do not appear as relevant properties for high catalytic activity. Nine new formulations were found to perform better than the reference catalyst “high surface area (HSA) ceria” (Rhodia).

Cobalt and KNO 3 supported on alumina catalysts for diesel soot combustion

The catalytic combustion of diesel soot was studied in the presence of fresh and aged catalysts: Co/Al 2O 3, KNO 3/Al 2O 3 and Co/KNO 3/Al 2O 3. The catalysts were prepared by impregnation using nitrate solutions. The catalysts were characterized by X-ray diffraction, thermal programmed reduction, vibrational spectroscopy and X-ray photoelectron spectroscopy. Fresh and aged catalysts present high activity in presence of O 2 and O 2/NO. The values of the combustion temperature decrease more than 200 °C with respect to that observed in the process without catalysis. The activity is associated with the presence of KNO 3 and the role of this salt can be attributed to the contribution of NO 3 −/NO 2 − redox cycle.

Catalytic combustion of diesel soot: Experimental design for laboratory testing

In order to abate diesel soot particles many catalysts have been studied at several industrial and academic laboratories. However, the comparison of kinetic data obtained with such catalysts is not straightforward, due to the different experimental conditions used in the activity measurement carried out by each research group. Temperature-programmed analysis is the most common technique used to determine catalytic activity for soot oxidation. For a given catalyst, the temperature-programmed oxidation profile depends on variables such as heating rate, oxygen partial pressure, gas flow rate, catalyst:soot weight ratio, type of contact between the catalyst and the soot, and existence of energy and/or mass transfer limitations during the analysis. This work presents a systematic study of the influence of all these testing variables on the TPO profile, and the optimum testing conditions to obtain good reproducibility during the kinetic study. Both experimental and computer simulation results are included to assist researchers in the comparison of results obtained under different experimental conditions.

Zirconia-Supported Cu-KNO3 Catalyst: Characterization and Catalytic Behavior in the Catalytic Combustion of Soot with a NO/O2 Mixture

The catalytic combustion of diesel soot was studied in the presence of catalysts: CuZrO2, KNO3ZrO2, and CuKNO3ZrO2. The catalysts were prepared by impregnation of ZrO2·nH2O into an aqueous solution of Cu(NO3)2, KNO3, or both salts simultaneously. The catalysts were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and temperature-programmed reduction (TPR). Cu(n)KNO3ZrO2 catalysts present high activity, and the value of the combustion temperature decreases 200 °C with respect to the temperature of the process without catalyzing, with Tmax values between 370 and 380 °C. The activity is associated with KNO3 presence, and the role of KNO3 can be attributed to (i) an increase of contact between soot and the surface of the catalyst and (ii) a redox reaction in which the nitrate is reduced to nitrite by reaction with carbon and again reoxidized to nitrate. The copper contribution is associated with the reaction selectivity toward CO2 formation.

High-throughput approach to the catalytic combustion of diesel soot

A methodology for the evaluation of diesel soot oxidation catalysts by high-throughput (HT) screening was developed. The optimal experimental conditions (soot amount, catalyst/soot ratio, type of contact, composition and flow rate of gas reactants) ensuring a reliable and reproducible detection of light-off temperatures in a 16 parallel channels reactor were set up. The temperature profile measured in the catalyst/soot bed under TPO conditions when the exothermic combustion of soot takes place was shown to provide an accurate measurement of the ignition. Its reproducibility and relevance were checked. The results obtained with a reference noble metal free catalyst (La 0.8Cr 0.8Li 0.2O 3 perovskite) agree very well with literature data. Qualitative mechanistic features could be derived from these experiments, stressing the likely limiting step of oxygen transfer from catalyst surface to soot particulates to ignite the soot combustion. Ceria material was shown to be more appropriate than perovskite one. From an HT screening of a large diverse library (over 100 mixed oxides catalysts) under optimized conditions, about 10 new formulations were found to perform better than selected noble metal free reference materials.

Catalytic combustion of diesel soot over K 2NiF 4-type oxides La 2- xK xCuO 4

Nanostructure K 2NiF 4 type oxides La 2- x K x CuO 4 complex oxides were prepared using the Sol-Gel method, characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared (FT-IR), and Scanning Electron Microscopy (SEM). The catalytic activity for soot combustion was evaluated by the Temperature-Programmed Reaction (TPO) technique. The results demonstrated that the substitution quality of K + for La 3+ at the A-site would increase the catalytic activities of La 2- x K x CuO 4 for soot combustion greatly; the substitution quality affected the structure and catalytic activity obviously. The La 1.8K 0.2CuO 4 complex oxides with tetrahedral structures had the best catalytic activity for soot combustion, and the ignition temperature of soot combustion was lowered from 490 to 320 °C.

Kinetics of the catalytic combustion of diesel soot with MoO3/Al2O3 catalyst from thermogravimetric analyses

Abstract Catalytic combustion of diesel soot was performed over a 15-wt.% MoO3/Al2O3 catalyst in a thermogravimetric analysis (TGA) system, at distinct heating rates and particulate concentrations. Kinetic parameters were then estimated for several experimental conditions, based on a first-order kinetic model and on the numerical integration of the differential mass balance equations. The estimated values of activation energies lie between 139 and 163 kJ/mol, in accordance with published data for similar systems. The analysis of the parameter estimates shows that the so-called compensation effect is a mere consequence of parameter correlation, which can be easily removed through reparameterization of the Arrhenius equation. Finally, it is shown that the proposed kinetic model provides suitable fits for the available experimental data. Besides, it is shown that thermogravimetric analysis, with simultaneous parameter estimation, can improve the statistical significance of the obtained results and lead to better understanding of the analyzed process.