Combustion Applications Research Articles

Combustion of lean ammonia-hydrogen fuel blends in a porous media burner

Ammonia offers a carbon-free fuel alternative for industrial heating, power generation and transportation. However, its low flame speed and high NOx emission represent significant challenges for combustor applications. The present study investigates the use of porous media burners (PMBs) to stabilize lean NH3/H2/air flames. By stabilizing the flame at the interface between two thermally conductive ceramic foams, internal heat recirculation preheats the reactants and increases the flame speed, which increases the combustion stability limits to very lean NH3/H2/air mixtures. Experimental studies are conducted to determine the stability limits of porous media combustion over a wide range of NH3/H2 volume ratios, equivalence ratios and mass fluxes. The NH3/H2 ratio is found to play a significant role with a typical dependency of the equivalence ratio at extinction in the form ϕext∝XH2−0.3. NOx emissions were shown to reach their minimum when the burner was operated near its extinction limit and to increase with increasing mass flux rates. Because unburnt NH3 emissions were also quite low (1400 ppm) at these very lean conditions, this operating regime offers similar or better emissions compared to the commonly employed fuel-rich operation which has been suggested in the literature.

Lattice-Boltzmann modeling of lifted hydrogen jet flames: A new model for hazardous ignition prediction

This numerical study deals with the hazardous ignition of a jet flame in a vitiated co-flow. A novel formulation, based on a passive scalar variable, will be presented to predict hydrogen auto-ignition events. The model, derived from the theoretical analysis of the Jacobian, correctly describes the appearance and absence of auto-ignition in complex configurations based on initial thermodynamic and mixture conditions. No chemical reaction and species equations are required to perform the simulations. Results of Lattice Boltzmann Methods (LBM) simulations of a 3D H2/N2 Cabra flame will be presented using a detailed H2-Air mechanism. Validation against experimental and numerical results will be provided for the lift-off (distance to auto-ignition). The passive scalar predictions are successfully compared with the reactive simulations. The results show a potential extension of this model to an extensive spectrum of hydrogen safety and large-scale turbulent combustion applications.

Non-Premixed Filtered Tabulated Chemistry for LES: Evaluation on Sandia Flames D and E

The non-premixed filtered tabulated chemistry for large eddy simulations employs numerical filtering to resolve a thin flame front on practical LES numerical grids. The flame structure is modified to be coherent with the domain discretization. The first turbulent combustion application of the non-premixed filtered tabulated chemistry approach is presented. A keen comparison of the flamelet filtering transformation in the premixed and non-premixed regimes is carried out. Three distinctive features are outlined: the flame thickness variation, the filtered manifold transformation, and the model activation dependence on the chosen diffusion flamelet configuration for a non-premixed filtered approach. The model performance is assessed on two real turbulent flame configurations, Sandia flames D and E, employing a three-dimensional tabulation strategy, where the numerical grid is coupled with the model by the third parameter, i.e., the computational cell size. The repercussions of the above cited aspects are carefully assessed. The results demonstrate that the formalism coupling with an SGS modeling function can adequately describe wrinkled flame front effects. The predictions for both the major stable species and the minor ones accurately correspond with the underlying physics. It turns out that there is a substantial variation of the filter effect as a function of the strain rate of the flame and the considered species. The varying filter sensitivity along the manifold influences the response of the model correction terms and the retrieved variables. The non-premixed FTACLES formalism possibilities and conditions for the model’s utilization and optimal performance are clearly stated, to confirm the idea that SGS closure in diffusive combustion can be derived based on filtering arguments, and not only based on statistical approaches.

Large-Eddy Simulation of two secondary air supply strategies in kraft recovery boilers

Kraft recovery boilers are large scale combustion applications operating on black liquor, a common side-product of the pulp industry. Here, a simplified boiler model utilizing Computational Fluid Dynamics (CFD) with Large-Eddy Simulation (LES) and Lagrangian Particle Tracking (LPT) is explored to better understand the secondary air supply system and the dispersion of sprayed droplets. The unsteady nature of the air jets and droplet dispersion in such context advocates the usage of scale-resolving simulations such as LES. In the present exploratory study, the usage of LES in recovery boiler air jet simulations is piloted for the first time. The air supply system is modeled as high-momentum-flux jets injected to a uniform cross-flow. First, the set-up was verified by performing a mesh sensitivity study. The main observed global flow features included the mixing zones, wall jet and jet impact regions, jet bending in cross-flow, and reverse flow downstream of the jets. Two different engineering relevant air supply systems, a staggered and an in-line configuration, were studied and compared in terms of mixing and droplet dispersion. The main findings of the present study are as follows. First, out of the two studied configurations, the staggered one was observed to provide a more uniform downstream temperature field. Second, the in-line configuration was noted to outperform the staggered configuration in droplet dispersion by having 22% less spray-wall impingement and 15% more droplets landing at the bottom of the furnace. Third, different modes for droplet trajectories were identified based on the global flow structures.

Flow/flame and emissions fields of premixed oxy-methane stratified flames in a dual annular counter-rotating swirl burner

Dual Annular Counter-Rotating Swirl (DACRS) premixed oxy-methane flames for nine different cases were studied numerically in a Dual-Stage Lean Premixed (DLPM) combustor for gas turbine combustion applications. The combustor consists of two streams, a primary central stream and a secondary annular one swirling in opposing directions. For all cases, the primary and secondary oxygen fraction (OF: O2%vol. in O2/CO2 oxidizer) was maintained at 30%, and the equivalence ratios (φ) of the primary and secondary streams were set to 0.9 and 0.55, respectively. Three different velocities were investigated for the primary central stream, and for each primary stream velocity, three different secondary velocities were considered to explore flow/flame interactions. The results show that: for all primary flow velocities, decreasing the secondary flow velocity led to the flame becoming thin and slightly elongated. The zone of peak local temperatures was concentrated in the flame core downstream of the center-body near the primary flow inlet as the secondary flow velocity was reduced. The magnitude of axial velocity has an effect on the flow distribution up to the first one-third section of the combustor. The mixture velocity varies inversely with Da number towards the combustor's exit. The thermal effect of secondary stream velocity starts around 40% away from the burner surface. Species distributions show that complete combustion is achieved and excess oxygen leaves the combustor with products due to the lean mixture of the secondary flow stream. The peak of product formation rate (PFR) is affected by flow streams velocities. Stable flames with reduced emissions were obtained over wide range of inlet velocities indicating the effectiveness of DLPM combustion approach for wider operability of gas turbine combustors.

Numerical study on self-ignition temperature of biomass gasified gas for the application of MILD combustion

Moderate and intense low-oxygen dilution (MILD) combustion of biomass gasified gas (BGG) has great potential. However, self-ignition temperature (Tsi) of BGG is not clear, which limits the establishment of BGG MILD combustion. In this study, Tsi of BGG was calculated in a perfectly stirred reactor using NUIG-NGM-2010 mechanism. Tsi of BGG/O2/N2 mixture was identified by the S-shape curve. Very wide ranges of the residence time τ (10−5 s–10 s), oxygen concentration XO2 (0.1%–35%) and equivalence ratio Φ (0.4–2.8) were considered. Results show that τ = 1 s was reasonable for MILD combustion. Tsi decreased with the increase of XO2. Tsi first decreases and then increases with the increases of Φ. BGG is easier to establish MILD combustion than CH4 because the critical XO2 is 11.7%, which is larger than CH4 (9.7%). Sensitivity analysis shows that R1 (H + O2 = O + OH) and R4 (O + H2O = OH + OH) are the most sensitive reaction for promoting ignition. R3 (OH + H2 = H + H2O), R21 (H2O2 + OH = H2O + HO2) and R13 (HO2 + OH = H2O + O2) were key reactions for prohibiting ignition under designed conditions.

Effects of radiation reabsorption on the flame speed and NO emission of NH3/H2/air flames at various hydrogen ratios

Ammonia has attracted extensive attention in the direct combustion applications due to its carbon–neutral properties. In this study, the numerical simulations of NH3/H2/air one-dimensional premixed laminar flame under the stoichiometric condition with different H2 ratios (η = XH2/(XNH3 + XH2) = 0.2–0.7) were conducted to explore the influence of radiation reabsorption on laminar flame speed and NO emission. Also the effect of radiation reabsorption on NO generation and emission in NH3/H2/air mixture when η = 0.6 with different equivalence ratios was discussed. The results showed that the radiation reabsorption effect on flame speed decreased monotonically with the H2 ratio increasing from 0.2 to 0.7, and the maximum effect was 17%. The effect on flame speed was regulated by the combination of direct radiation effect and chemical effect, which was influenced by reaction R257 NH2 + NO = NNH + OH via OH radical when η = 0.2–0.7 and ϕ = 1.0. The promotion effect of radiation reabsorption on NO generation and emission decreased monotonically with the increasing H2 proportion. The enhancement of NO generation caused by radiation reabsorption was mainly controlled by R222 N + OH<=>NO + H. On the other hand, R220 N + NO<=>N2 + O, R240 NH + NO = N2O + H and R242 NH + NO = N2 + OH affected the NO emission in the post-flame zone. At η = 0.6 and ϕ = 0.65–1.5, the promotion of NO generation by radiation reabsorption was non-linear, which was mainly affected by R257, R241 NH + NO = N2O + H and R222 reactions. The NO emission was mainly influenced by R241 and R233 in the post-flame zone at ϕ = 0.65–1.05. And R241, R242, R256 NH2 + NO = N2 + H2O and R257 in the post-flame zone dominated the NO emission when ϕ > 1.05.

Numerical study of experimental feasible heat release rate markers for NH3–H2-air premixed flames

Ammonia (NH3) and hydrogen (H2) as carbon-free fuels have attracted much attention for combustion applications in recent years. Co-firing ammonia with hydrogen provides a solution to overcome the extremes in the reactivities of both pure ammonia and hydrogen fuels. Heat release rate (HRR) is one of the most important quantities in the study of turbulent combustion, but direct measurement of local HRR is not experimentally feasible. In this study, we explored several quantities, [NH], [O], and the gradient of [OH] (Grad [OH]) as potential experimentally feasible HRR markers for NH3–H2-air premixed flames using numerical simulations. The performance of these quantities over a wide range of equivalence ratios and H2 blending ratios have been examined, and some key reactions have been identified to explain the corresponding variations of the correlation for [NH] and [O]. It is concluded that the [NH] and Grad [OH] can be used in general as a suitable HRR marker for NH3–H2-air premixed flames, and the use of [NH] is especially recommended for lean flame conditions. A strategy that slightly shifts the [NH] and Grad [OH] profiles to overlap the corresponding HRR shows a further improvement on the performance of [NH] and Grad [OH]. The use of [O] can be considered for rich flame conditions while cautions are needed for conditions with high H2 blending ratios.

Recent progress in the development of synthetic oxygen carriers for chemical looping combustion applications

Continuously rising concentrations of CO2 in the atmosphere has led to significant negative impacts on the environment which propelled research efforts to replace fossil fuel-based energy with clean energy sources. However, the reliance on fossil fuel as the main energy source is projected to stay for many years to come, and therefore developing cleaner pathways to utilize fossil fuels for energy generation is paramount. Chemical looping combustion (CLC) has emerged in recent years as a promising technology for CO2 capture in power plants and other CO2 intensive industries. A key cornerstone for CLC is the development of efficient oxygen carriers with high oxygen capacity, fast kinetics, cyclic stability, mechanical strength, and low cost. The research progress in this field is rapidly growing to tackle the major materials and operational challenges to advance the knowledge toward a commercial scale CLC application. This work provides an overview of the significant advancements achieved over the past seven years in the development of synthetic metal oxide-based oxygen carriers. A summary of key performance indicators used to evaluate oxygen carriers is presented in this study to enable for a systematic assessment of the oxygen carriers’ properties and performance. This work is focused on summarizing and critically reviewing the literature on the development of oxygen carriers such as Ni, Cu, Fe, Mn, Co-based metal oxides and combined/mixed oxygen carriers in the past seven years. Studies of naturally occurring materials and waste materials used as oxygen carriers are excluded from this review which is mainly focused on synthetically prepared materials. Significant efforts were dedicated to investigating the role of the supports, synthesis methods, promotors, and other factors affecting the CLC performance of synthetic oxygen carriers using solid, liquid, and gaseous fuels. This review also outlines the main challenges, research needs and opportunities for future progress to highlight potential pathways to develop synthetic oxygen carriers in an environmentally friendly, and cost-effective manner.

A comparative study of gaseous fuel flame characteristics for different bluff body geometries

Flame stabilization by a bluff-body is commonly used in many combustion applications to improve mixture characteristics, enhance flame stability and assist in combustion control. The main objectives of the present experimental work are concerned with studying the flame stabilization and combustion characteristics of Liquefied Petroleum Gas (LPG) with different bluff body shapes and sizes. An experimental test rig that consists of a gaseous fuel line, compressed air line, mixing chamber and burner is designed and constructed. Different bluff body shapes such as disc, cone, V-gutter, horizontal and vertical cylinders are used. The effects of different Blockage Ratios (B.R.) of 0.25, 0.35, 0.45, and 0.55 are studied at a constant equivalence ratio (Փ) of 1.85 for different bluff body shapes. The blowoff limits, temperature distributions, flame shapes, exhaust species concentrations and visible flame length are experimentally measured and discussed. The results indicated that increasing the blockage ratio leads to increasing the maximum flame temperature, increasing the flame diameter, and decreasing the flame length for all bluff body shapes. The centerline axial NO concentration has its peak values coincide with the maximum centerline axial temperatures. The flame using bluff body cone is more stable than using other bluff body shapes i.e., it has wide flammability limits or a wide range of operating conditions.

Reduction kinetics of combusted iron powder using hydrogen

Despite extensive research on reduction of iron oxides in literature, there is no consensus on the most accurate reduction kinetics, especially for micron-sized iron oxide powders with high purity. Such data is particularly important for the application of metal fuels and chemical looping combustion, in which high purity iron powders function as dense energy carriers. Hence, in this work, hydrogen reduction of iron oxide fines, produced by iron combustion, were investigated using thermogravimetric analysis (TGA). The isothermal reduction experiments were conducted at the temperature range of 400–900 °C and at hydrogen partial pressures of 0.25–1.0 atm. Scanning electron microscopy (SEM) showed that the morphology of the reduction products depends on the reduction temperature but not on the hydrogen partial pressure. Reduction at higher temperatures leads to larger pore sizes. Based on an extended Hancock-Sharp “lnln”-method the appropriate gas-solid reaction models are determined, suggesting that the reduction can be described by a single-step phase boundary controlled reaction at temperatures below 600 °C, whereas a multistep mechanism is required for the description of reactions at higher temperatures.

Simultaneous Impact of Hollow Droplet and Continuous Dense Droplet on Liquid Film

The Simultaneous impact of a hollow droplet and a continuous dense droplet on a liquid film was investigated using the coupled level set and volume of fluid (CLSVOF) method. Analyses included fluid dynamics and heat transfer characteristics in impact. Results showed that the interfacial phenomena after impact incorporates spreading, central jet between droplets, edge liquid sheet, and counter jet inside the hollow droplet. The pressure gradient is the major cause for the above phenomena. The significant parameter of impact velocity is closely related to the dynamics and heat transfer for droplets impacting on a liquid film. Droplets with higher impact velocity exhibit a greater spreading factor, central jet height, edge jet height, and counter jet height. Besides, wall heat flux increases more notably for droplets with a higher impact velocity. Compared with the continuous droplet, the hollow droplet shows a smaller spreading factor and edge jet height, a higher wall heat flux, but a narrow thermally affected region. This study provides a fundamental understanding for the application of high-pressure spray combustion.

Evaluation of flamelet/progress variable model for the applications in supersonic combustion using hybrid RANS/LES approach

The Flamelet/Progress Variables (FPV) model coupled with large eddy simulation (LES) has been performed to appraise its applicability and performance for supersonic hydrogen combustion, based on the simulations of strut based scramjet and cavity based combustors. For the two typical schemes involved in the present work, the validation of the numerical solver compiled by in-house code is realized by the comparisons with the experimental measurements including temperature, velocity, and wall pressure. The methods for calculating mixture fraction variance in the framework of LES are also investigated and examined in both cases. It can be observed that the diffusion combustion mode is in the dominant state for the whole reactive zone in both cases, where the FPV model is physically compatible. Through the comparisons of the scale similarity method and the transport equation method for calculating mixture fraction variance, the importance of calculating this sub-grid turbulent scalar flux is emphasized. The results show that the mixture fraction variance calculated by the scale similarity model is locally high, but its diffusion is insufficient, which makes the local temperature of the combustion flow field overpredicted and concentrated. On the contrary, the transport equation of the mixture fraction variance can overcome this problem and improve the combustion prediction accuracy, thus, it is more recommended if the computing resources are guaranteed. Qualitatively, the Flamelet/Progress Variables (FPV) model with the large eddy simulation approach can accurately capture the structure and characteristics of the supersonic combustion flow field.

Revisiting low temperature oxidation chemistry of n-heptane

Benefitting from the rapid development of instrumental analysis methods, intermediate products that were difficult to probe in the past can now be measured and quantified in complex reaction systems. To understand low temperature reactions of interest for combustion applications, and reduce the deviations between model predictions and experimental measurements, constant advancement in understanding low temperature oxidation process is necessary. This work examines the oxidation of n-heptane in jet-stirred reactors at atmospheric pressure, with an initial n-heptane mole fraction of 0.005, equivalence ratio of 0.5, a residence time of 1s, and over a temperature range of 500-800 K. Reaction products were analyzed using synchrotron ultra-violet photoionization mass spectrometry, gas chromatography, and Fourier-transform infrared spectroscopy. Ignition delay times of n-heptane/O2/CO2 mixture were measured in a rapid compression machine at 20 and 40 bar over a 600-673 K temperature range. Based on the experimental results, a comprehensive kinetic model of n-heptane low temperature oxidation was developed by considering the sub-mechanisms of keto-hydroperoxide, cyclic ether, heptene isomers, and the third O2 addition reaction, and by updating the rate constants of keto-hydroperoxide decomposition and second oxygen addition reactions. The combination of reaction mechanism development and evaluation of the rate constants of key reactions enabled the model to effectively predict the species concentrations and ignition delay times of n-heptane low temperature oxidation, providing additional insight into alkane low temperature oxidation chemistry.

Residential Fuel Transition and Fuel Interchangeability in Current Self-Aspirating Combustion Applications: Historical Development and Future Expectations

To reduce greenhouse gases and air pollutants, new technologies are emerging to reduce fossil fuel usage and to adopt more renewable energy sources. As the major aspects of fuel consumption, power generation, transportation, and industrial applications have been given significant attention. The past few decades witnessed astonishing technological advancement in these energy sectors. In contrast, the residential sector has had relatively little attention despite its significant utilization of fuels for a much longer period. However, almost every energy transition in human history was initiated by the residential sector. For example, the transition from fuelwood to cheap coal in the 1700s first took place in residential houses due to urbanization and industrialization. The present review demonstrates the energy transitions in the residential sector during the past two centuries while portending an upcoming energy transition and future energy structure for the residential sector. The feasibility of the 100% electrification of residential buildings is discussed based on current residential appliance adoption, and the analysis indicates a hybrid residential energy structure is preferred over depending on a single energy source. Technical considerations and suggestions are given to help incorporate more renewable energy into the residential fuel supply system. Finally, it is observed that, compared to the numerous regulations on large energy-consumption aspects, standards for residential appliances are scarce. Therefore, it is concluded that establishing appropriate testing methods is a critical enabling step to facilitate the adoption of renewable fuels in future appliances.

Ignition and combustion of Perfluoroalkyl-functionalized aluminum nanoparticles and nanothermite

Aluminum (Al) is an excellent metal fuel for combustion applications because of its high energy density and low cost. Nano-sized Al (nAl) particles have relatively low ignition temperature and high reactivity, but their performance is limited by the presence of the native oxide (Al2O3) layer surrounding the active Al core. To overcome this problem, nAl coated or mixed with fluorocarbon species have been intensively studied recently. In this work, we demonstrate a facile method to functionalize the surface of nAl particles with perfluoroalkylsilane and investigate the thermochemical and combustion behaviors of perfluoroalkyl-functionalized nAl particles at both slow and fast heating rates. At slow heating rates, the covalently-bonded perfluoroalkylsilane molecules partially undergo debonding at low temperatures before reacting with Al2O3. The remaining perfluoroalkyl molecules slowly react with surface oxide to thicken the surface shell, which improves the thermal stability of nAl particles. Nevertheless, under fast heating conditions, the dissociated fluorine species can readily react with the oxide on the nAl surface, enhancing the ignition and combustion performance of both nAl particles in the air and Al/copper (II) oxide (CuO) nanothermite. These results advance the understanding of the thermochemical behaviors of the fluorocarbon species and their effects on the ignition and combustion of nAl particles and Al-based energetic materials.

Simulation of CO2 Capture Process in Flue Gas from Oxy-Fuel Combustion Plant and Effects of Properties of Absorbent

Oxy-fuel combustion technology is an effective way to reduce CO2 emissions. An ionic liquid [emim][Tf2N] was used to capture the CO2 in flue gas from oxy-fuel combustion plant. The process of the CO2 capture was simulated using Aspen Plus. The results show that when the liquid–gas ratio is 1.55, the volume fraction of CO2 in the exhaust gas is controlled to about 2%. When the desorption pressure is 0.01 MPa, desorption efficiency is 98.2%. Additionally, based on the designability of ionic liquids, a hypothesis on the physical properties of ionic liquids is proposed to evaluate their influence on the absorption process and heat exchanger design. The process evaluation results show that an ionic liquid having a large density, a large thermal conductivity, and a high heat capacity at constant pressure is advantageous. This paper shows that from capture energy consumption and lean circulation, oxy-fuel combustion is a more economical method. Furthermore, it provides a feasible path for the treatment of CO2 in the waste gas of oxy-fuel combustion. Meanwhile, Aspen simulation helps speed up the application of ionic liquids and oxy-fuel combustion. Process evaluation helps in equipment design and selection.

On the use of ammonia as a fuel – A perspective

Ammonia has long been considered as a candidate vector for power generation, and has specifically gained significant interest recently. Though it is not free of drawbacks, ammonia has been identified as a promising potential alternative fuel for future power generation. Current studies and a growing body of works in this direction drive us closer to a viable solution of ammonia as an important transition into a cleaner future of the energy sector. In this perspective, we explore the use of ammonia as a fuel in combustion applications (with and without additives) and in fuel cells. The objective of this work is to show the prospects and challenges of ammonia as a fuel, and suggest significant topics that could benefit from additional studies.

Effect of oxidative torrefaction on particulate matter emission from agricultural biomass pellet combustion in comparison with non-oxidative torrefaction

Torrefaction could improve the fuel properties and reduce the operating costs. However, the particulate matter (PM) emission behavior during the torrefied pellet combustion remains unknown. In this work, cotton stalk was torrefied at a temperature of 220–300 °C with a O2 concentration of 0–21%. The torrefied pellet was burned out and PM emission behavior was investigated using a Dekati low-pressure impactor. The results show that oxidative torrefaction leads to notable decreases of H/C and O/C ratios, which makes the fuel properties similar to coals. The heating value is significantly improved and sensitive to the torrefaction temperature. Both non-oxidative and oxidative torrefaction give rise to considerable increase in the yield of PM10. The main composition of PM1 changed from KCl to K2SO4 due to the substantial release of Cl during torrefaction. Meanwhile, Ca and K contents in PM1-10 are generally high, implying that the presence of oxygen can facilitate the transformation of alkali and alkaline-earth metals into coarse particles. The torrefaction temperature at around 260 °C with a low O2 concentration of 0–6% are the optimal torrefaction operation conditions to produce good quality torrefied cotton stalk pellet with respect to high heating value and low PM emission in later combustion application.

Preparation of Cordierite Monolith Catalysts with the Coating of K-Modified Spinel MnCo2O4 Oxide and Their Catalytic Performances for Soot Combustion

Diesel engines are important for heavy-duty vehicles. However, particulate matter (PM) released from diesel exhaust should be eliminated. Nowadays, catalytic diesel particulate filters (CDPF) are recognized as a promising technology. In this work, a series of monolith Mn1−nKnCo2O4 catalysts were prepared by the simple citric acid method. The as-prepared catalysts displayed good catalytic performance for soot combustion and the Mn0.7K0.3Co2O4 catalyst gave the best catalytic performance among all the prepared samples. The T10 and Tm of Mn0.7K0.3Co2O4-HC catalyst for soot combustion are 310 and 439 °C, respectively. The physical and chemical properties of catalysts were characterized by means of SEM, XPS, H2-TPR, Raman and other techniques. The characterization results indicate that K substitution is favorable for the formation of oxygen vacancies, enhancing the mobility of active oxygen species, and improving the redox properties and so on. In-situ Raman results prove that the strength of Co-O bonds in the catalysts became weak during the reaction at high temperatures. In addition, SEM and ultrasonic test results show that the peeling rate of the coat-layer is less than 5%. The as-prepared catalysts can be taken as one kind of candidate catalyst for promising application in soot combustion because of its facile synthesis, low cost and high catalytic activity.