Catalytic Combustion Activity Research Articles

Effects of Ce in the catalytic combustion of toluene on CuxCe1-xFe2O4

CuxCe1-xFe2O4 (x = 0, 0.2, 0.5, 0.8, 1) catalysts were synthesized by a sol-gel auto-combustion method, and the catalysts were characterized by differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), H2-temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The activity of CuxCe1-xFe2O4 was evaluated in the catalytic combustion of toluene in a fixed-bed reactor. The results indicated that the Cu0.8Ce0.2Fe2O4 expressed the highest catalytic combustion activity of toluene, the ignition temperature (T50) and the complete conversion temperature (T90) were 180 °C and 215 °C, respectively. The Ce doping of CuFe2O4 could increase the oxygen storage capacity and improve the catalytic combustion activity of toluene. The CuFe2O4 spinel crystal structure gradually disappeared with the increase in Ce doping; at the same time, the catalytic combustion activity of the samples was obviously affected.

LaMnO<sub>3</sub> (La<sub>0.8</sub>Sr<sub>0.2</sub>MnO<sub>3</sub>) Perovskites for Lean Methane Combustion: Effect of Synthesis Method

The effect of the preparation method on the properties of LaMnO3 and La0.8Sr0.2MnO3 perovskite was studied. Materials were prepared by four methods: sol-gel, chemical combustion, solvothermal and spray pyrolysis and characterized. The effect of the synthesis method on the texture, acid-base character of the surface, reducibility with hydrogen, oxygen desorption, surface composition and catalytic activity for combustion of lean methane was studied. It was found that synthesis method affects physicochemical properties of obtained materials-solvothermally produced materials exhibit well-developed surface area, presence of reactive oxygen species on surface and high catalytic activity for CH4 combustion. Generally, LaMnO3 and La0.8Sr0.2MnO3 perovskites show catalytic activity for lean CH4 combustion comparable or higher than the activity of 0.5 wt.% Pt/Al2O3 but lower than 1 wt.% Pd/Al2O3.

CoMnxOy nanosheets with molecular-scale homogeneity: an excellent catalyst for toluene combustion

The redox–precipitation technique yields molecularly dispersed CoMnxOy nanosheets with improved physicochemical properties compared to those obtained by a conventional co-precipitation method, leading to excellent catalytic activity in toluene combustion.

The relationship between the chemical state of Pd species and the catalytic activity for methane combustion on Pd/CeO2

Three Pd/CeO2 catalysts are synthesized by reduction-deposition and an impregnation method (IMP) to clarify how the chemical state of Pd influences the catalytic performance for CH4 combustion.

Facile synthesis of three-dimensional ordered macroporous Sr1−xKxTiO3 perovskites with enhanced catalytic activity for soot combustion

The appropriate incorporation of potassium into 3DOM SrTiO3 perovskites effectively improved the catalytic performance for soot combustion.

Al2O3-CeO2 Oxides: Synthesis, Characterization and Evaluation as Catalytic Supports in Benzene Combustion. Surface Ceria Effects

Abstract Al2O3-CeO2 sol-gel oxides were obtained at ceria loadings of 2, 5, 10, 20 and 50 wt.%, calcined at 700 °C and characterized by N2 physisorption, XRD, TEM, 27Al MAS-NMR, and TPR. All samples present high amounts of surface ceria species and bulk ceria has significant presence from 20 wt.% of ceria. The sample with 50 wt.% presents both the reduction of bulk and interfacial ceria species and X-ray diffraction peaks corresponding to cerianite phase. Surface ceria dispersion degree (surface ceria/total reduced ceria) was determined to be 100 % for samples with 2 and 5 wt.% CeO2, with a slight decrease to ca. 90 % and 75 % for samples with 10 and 20 wt.% CeO2 respectively, and a lower value of 41 % for the sample with 50 wt.% CeO2. It was found the amount of surface ceria has a good correlation with the amount of AlV sites, indicating that incorporated Ce ions distorts the alumina matrix and restricts the amount of surface ceria. Platinum supported on these materials showed that the catalytic activity in benzene combustion for oxygen-depleted environments increased as the surface ceria concentration increased.

Supported and unsupported manganese oxides for catalytic ammonia combustion

We study the catalytic combustion properties of supported and unsupported manganese oxides (MnOx) with NH3 (a carbon-free energy source). Unsupported MnOx with higher oxidation states tends to exhibit higher catalytic NH3 combustion activity (MnO2>Mn2O3>MnO). X-ray diffractometry (XRD) and absorption fine structure (XAFS) analysis show that MnO2 reduces to Mn2O3 after the combustion reaction. Among the MnOx (5wt% Mn) supported on various materials, MnOx/CeO2 exhibited the highest activity. Analysis of XPS (X-ray photoelectron spectroscopy) spectra before and after the reaction suggests that the oxidation state of CeO2-supported MnOx is a mixture of Mn2+ and Mn3+.

Effect of coating modification of cordierite carrier on catalytic performance of supported NiMnO3 catalysts for VOCs combustion

NiMnO3 perovskite catalysts supported on cordierite modified by CexZr1-xO2 coatings were prepared using impregnation and sol–gel methods for catalytic combustion of single/double component VOCs at different concentrations and GHSV of 15,000 h−1, which were characterized by BET, XRD, SEM, FT-IR, H2-TPR and O2-TPD. After coating modification, the specific surface area of catalysts is improved obviously. Among the catalysts, the Ce0.75Zr0.25O2 coating modified NiMnO3 catalyst exhibits the best catalytic activity for VOCs combustion with 95.6% conversion at 275 °C and has stable activity when catalyst is embalmed at 800 °C. In addition, the catalyst also presents the excellent water-resistant and conversion stability over time-on-stream condition. The reason is that Ce0.75Zr0.25O2 coating can promote more lattice distortion and defects and smaller crystal size, which improve oxygen transfer capability and dispersion of active component.

Hydrothermal synthesis of NiCeOx nanosheets and its application to the total oxidation of propane

A series of NiCeOx mixed metal oxide catalysts with various Ce/(Ce+Ni) ratios were prepared using hydrothermal methods The NiCeOx catalyst with a 4% Ce/(Ni+Ce) molar ratio (NiCeOx-4) demonstrated excellent catalytic performance for propane oxidation. Furthermore, the preparation method strongly affected the morphology and surface structure of the NiCeOx-4 catalyst as well as its catalytic activity for propane oxidation. The NiCeOx-4 catalyst that was prepared with the hydrothermal method exhibited a better catalytic performance compared with catalysts that were prepared by the co-precipitation method, sol-gel method and physical mixing of pure NiO and CeO2 powders. The results demonstrated that Ni-containing CeO2 (NiCeOx) nanoparticles were located on the surface of the NiCeOx-4 catalyst that was prepared using the hydrothermal method. As a result, the NiCeOx-4 catalyst had strong reducibility, a large number of active oxygen species, and strong ability to break the CH bond of propane, which led to higher catalytic activity for propane combustion.

Effects of support materials and silver loading on catalytic ammonia combustion properties

In this research, the effects of support materials and silver (Ag) loading on catalytic NH3 combustion properties were studied. Among the Ag supported on various metal-oxide materials, Ag/Al2O3 exhibited high catalytic NH3 combustion activity and high N2 (lowN2O·NO) selectivity. The combustion activity is closely associated with the Ag dispersion which is estimated using the O2–H2 titration technique. Thus, highly dispersed Ag nanoparticles on supports play a crucial role in the low-temperature light-off of NH3, implying that the support materials significantly affect the Ag dispersion. Although Ag/Al2O3 with higher amounts of Ag loading tended to exhibit higher combustion activity, the optimum Ag loading was found to be approximately 10wt.%. At the optimum Ag loading concentration, Ag/Al2O3 performed well during the catalytic NH3 combustion reaction. The local structures of the catalysts were investigated via transmission electron microscopy, X-ray absorption fine structure and gas adsorption techniques. After an NH3 combustion reaction at a temperature of 900°C, Ag/Al2O3 slightly deactivated because of the sintering of metallic Ag nanoparticles and the decreased surface area.

High rates of catalytic hydrogen combustion with air over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ Ti 0.97 Pd 0.03 O 2 - δ coated cordierite monolith

$$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta }$$ was coated on $$\upgamma \hbox {-}\hbox {Al}_{2}\hbox {O}_{3}$$ -coated honeycomb structured cordierite monolith (AHCM) by solution combustion method using dip-dry-heat process. This is a modified conventional method to coat the catalysts on honeycomb structured cordierite monolith (HCM). Formation of $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ on AHCM was confirmed by XRD. The XPS spectra of Pd(3d) core level confirmed Pd ion in $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ is in the form of +2 state. The surface morphology of coated catalyst was unchanged by long time exposure to hydrogen combustion reaction; i.e., $$\hbox {H}_{2} + \hbox {O}_{2}$$ recombination reaction which indicated the stability of coating on monolith. $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ showed high rates of $$\hbox {H}_{2} + \hbox {O}_{2}$$ recombination compared to 2 atom% Pd(metal)/ $$\upgamma \hbox {-}\hbox {Al}_{2}\hbox {O}_{3}$$ , $$\hbox {Ce}_{0.98}\hbox {Pd}_{0.02}\hbox {O}_{2-\updelta } $$ , $$\hbox {Ce}_{0.98}\hbox {Pt}_{0.02}\hbox {O}_{2-\updelta } $$ , $$\hbox {Ce}_{0.73}\hbox {Zr}_{0.25}\hbox {Pd}_{0.02}\hbox {O}_{2-\updelta }$$ , $$\hbox {Ti}_{0.99}\hbox {Pd}_{0.01}\hbox {O}_{2-\updelta } $$ and $$\hbox {Ti}_{0.98}\hbox {Pd}_{0.02}\hbox {O}_{2-\updelta } $$ . The activation energy of $$\hbox {H}_{2} + \hbox {O}_{2}$$ recombination reaction over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ is 7.8 kcal/mol. The rates of reaction over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ at 60 $$^{\circ }\hbox {C}$$ are in the range between 10 and 20 $$\upmu \hbox {mol/g/s}$$ . The rate of reaction over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ increased with increase in the concentration of $$\hbox {H}_{2}$$ . For 50 mL of $$\hbox {H}_{2}$$ , it showed rates of the reaction around 36.45 $$\upmu \hbox {mol/g/s}$$ at room temperature and 230 $$\upmu \hbox {mol/g/s}$$ at 60 $$^{\circ }\hbox {C}$$ . It was found that the rate of reaction due was lower due to hindering effect by adsorption of other gas molecules on the catalytic site. Finally, we propose a mechanism of hydrogen and oxygen recombination reaction over $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ . $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ catalysts were coated by solution combustion method on $$\upgamma \hbox {-}\hbox {Al}_{2}\hbox {O}_{3}$$ coated honeycomb structured cordierite monolith. Among the catalysts, $$\hbox {Ti}_{0.97}\hbox {Pd}_{0.03}\hbox {O}_{2-\updelta } $$ coated monolith showed high catalytic activity for hydrogen combustion with air. The proposed mechanism of $$\hbox {H}_{2} + \hbox {O}_{2}$$ reaction clarified that $$\hbox {Pd}^{+2}$$ ion state is unaltered in $$\hbox {Ti}\hbox {O}_{2}$$ lattice.

Three-dimensionally ordered macroporous LaMnAl11O19-supported Pd nanocatalysts highly active for methane combustion

Three-dimensionally ordered macroporous (3DOM) LaMnAl11O19 and 0.97wt% Pd/3DOM LaMnAl11O19 samples with a good-quality 3DOM structure have been prepared using the poly(methyl methacrylate) (PMMA)-templating and polyvinyl alcohol (PVA)-protected reduction methods, respectively. The Pd nanoparticles (NPs) with a size of 2–5nm were uniformly dispersed on the macropore wall surface of 3DOM LaMnAl11O19. Due to the highest adsorbed oxygen species concentration and the best low-temperature reducibility, the 0.97wt% Pd/3DOM LaMnAl11O19 sample showed the best catalytic activity for methane combustion, with the reaction temperatures (T10%, T50%, and T90%) required for achieving methane conversions of 10, 50, and 90% being 259, 308, and 343°C at SV=20,000mL/(gh), respectively. The 0.97wt% Pd/3DOM LaMnAl11O19 catalyst was catalytically stable, whereas the 0.98wt% Pd/3DOM Mn2O3 sample was partially deactivated after 50h of methane oxidation. The introduction of 3.0vol% H2O or 2.0 vol% CO2 to the reaction system resulted in the reversible deactivation of 0.97wt% Pd/3DOM LaMnAl11O19, but the addition of 100ppm SO2 led to the irreversible deactivation of the catalyst. It is concluded that the good-quality 3DOM structure, uniformly dispersed Pd NPs, high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between Pd NPs and 3DOM LaMnAl11O19 were accountable for the good catalytic performance of 0.97wt% Pd/3DOM LaMnAl11O19.

Study on the coating of nano-particle and 3DOM LaCoO3 perovskite-type complex oxide on cordierite monolith and the catalytic performances for soot oxidation: The effect of washcoat materials of alumina, silica and titania

The novel catalysts of LaCoO3/ɤ-Al2O3/cordierite monolith, LaCoO3/SiO2/cordierite monolith, LaCoO3/TiO2/cordierite monolith were prepared by using aluminum oxide, silicon dioxide and titanium dioxide nanoparticles as washcoat and monolithic cordierite as the monolithic ceramic substrate.The obtained samples were characterized by means of XRD, SEM, EDS, BET, and ultrasonic vibration test (Medi II Pselecta). The surface area of the cordierite monolith-supported LaCoO3/ɤ-Al2O3 is larger than those of LaCoO3/SiO2 and LaCoO3/TiO2. The coating of alumina, silica oxide and titania nanoparticles could increase the surface area of monolithic cordierite and also endue the coated layer with engineered structure. The results of thermal treatment experiment indicate that the good thermal stability of the ɤ-Al2O3 coating on the cordierite. The ultrasonic vibration test results showed that the washcoat was adhered to the substrate strongly. The weight loss for the samples LaCoO3/ɤ-Al2O3/cordierite (the most desired preparation protocol in this study) eventually reached about 3%, which was considered as a low weight loss.The LaCoO3/ɤ-Al2O3/cordierite monolith catalysts were successfully prepared by coating ready-made 3DOM LaCoO3 (perovskite-type oxides) catalysts onmonolithic cordierite substrate with a dip-coating method by employing aluminasol for the first time. The catalytic activities of a series of monolithic catalystsLaCoO3/ɤ-Al2O3/cordierite, LaCoO3/ɤ-Al2O3/cordierite (3DOM-catalysts), LaCoO3/SiO2/cordierite, LaCoO3/TiO2/cordierite were evaluated for soot combustion. Thenano LaCoO3/ɤ-Al2O3/cordierite catalysts gave the highest catalytic activity for soot combustion among the studied catalysts. The T10, T50, T90 over the LaCoO3/ɤ-Al2O3/cordierite catalyst were 199.4°C, 340.5°C, 405.3°C, respectively, and sco2m was 99.9%.

Plausibility of potassium ion-exchanged ZSM-5 as soot combustion catalysts

Potassium (K) ion-exchanged ZSM-5 zeolites were investigated for catalytic soot combustion. X-ray absorption fine-structure (XAFS), Raman, in situ IR and NH3-temperature programmed desorption (NH3-TPD) confirmed the location of K+ at the ion-exchanged sites. Temperature-programmed oxidation (TPO) reactions showed that K-ZSM-5 decreased ignition tempeatures of soot combustion and increased selectivity to CO2. The improved activity for soot combustion by increasing K+-exchanged amounts via decreasing the Si/Al ratio reinforced the K+ ions participating in soot combustion. 18O2 isotopic isothermal reactions suggested the activation of gaseous oxygen by the K+ ions. This demonstrated a new appliction of alkali metal exchanged zeolites and the strategy for enhancement of catalytic soot combustion activity.

Catalytic performance of Pd–NiCo2O4/SiO2 in lean methane combustion at low temperature

In this paper, the catalyst of Pd–NiCo2O4/SiO2 was prepared and applied to the catalytic combustion of lean methane. Pd and NiCo2O4 nanoparticles were uniformly distributed on the SiO2 support, so that every Pd or NiCo2O4 nanoparticle was separated from each other by another component. Comparing with Co3O4/SiO2, NiCo2O4/SiO2, Pd–Co3O4/SiO2 and Pd#NiCo2O4/SiO2 (catalysts without uniform distribution of Pd and NiCo2O4 nanoparticles), Pd–NiCo2O4/SiO2 had the highest catalytic activity in the catalytic combustion of lean methane, with a methane total conversion temperature at 378 °C. In addition, the high activity did not decrease during the long time reaction, which showed good thermal stability. TEM and BET results showed that the nanoparticle sizes of Pd and NiCo2O4 were very small. The XRD patterns indicated that the Pd nanoparticles were highly dispersed on the surface of SiO2. The XPS spectra demonstrated the formation of NiCO2O4, the presence of enough active oxygen species on the catalyst surface and the high ratio of PdO/Pd0. The enhanced influence of Ni introduction was also proved by comparison tests. All these results indicated that the high catalytic activity of Pd–NiCo2O4/SiO2 mainly comes from the nanoparticle distribution and the Ni cation enhancement.

Catalytic combustion of volatile aromatic compounds over CuO-CeO2 catalyst

Ce1−x Cu x O2 oxide solid solution catalysts with different Ce/Cu mole ratios were synthesized by the one-pot complex method. The prepared Ce1−x Cu x O2 catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and H2 temperature-programmed reduction (H2-TPR). Their catalytic properties were also investigated by catalytic combustion of phenyl volatile organic compounds (PVOCs: benzene, toluene, xylene, and ethylbenzene) in air. XRD analysis confirmed that the CuO species can fully dissolve into the CeO2 lattice to form CeCu oxide solid solutions. XPS and H2-TPR results indicated that the prepared Ce1−x Cu x O2 catalysts contain abundant reactive oxygen species and superior reducibility. Furthermore, the physicochemical properties of the prepared Ce1−x Cu x O2 catalysts are affected by the Ce/Cu mole ratio. The CeCu3 catalyst with Ce/Cu mole ratio of 3.0 contains abundant reactive oxygen species and exhibits superior catalytic combustion activity of PVOCs. Moreover, the ignitability of PVOCs is also affected by the respective physicochemical properties. The catalytic combustion conversions of ethylbenzene, xylene, toluene, and benzene are 99%, 98.9%, 94.3%, and 62.8% at 205, 220, 225, and 225 °C, respectively.

PdOx/Silicalite-1 Catalyst Prepared by Room Temperature Ozone Treatment: Preparation Chemistry and Catalytic Performance for Methane Combustion

The potential of ozone (O3) for preparation of supported metal catalyst remained unexplored. In this work, a two-step preparation method comprising ion-exchange and room temperature ozone treatment was developed to prepare a zeolite (silicalite-1) supported palladium catalyst. The fundamental preparation chemistry was examined by diffuse reflectance UV–Vis spectroscopy, IR and Raman spectroscopy, X-ray powder diffraction (XRD), and scanning transmission electron microscopy (STEM). While conventional thermal calcination produced PdOx particles mostly on the external surface of silicalite-1 crystals, ozone treatment produced PdOx clusters mostly within the zeolite crystals. Compared with thermal calcination, room temperature ozone treatment can significantly suppress the migration of palladium species outward to the external surface of the zeolite crystals. PdOx/silicalite-1 catalyst prepared with this method exhibited good catalytic activity and stability for catalytic methane combustion. The methane combustion started at about 250 °C; the T 50 and T 90 (the temperatures at which methane conversion reaches 50 and 90% respectively) were 345 and 403 °C, respectively. The conversion decreased slightly from 100 to 96.1% after 24 h of reaction at 500 °C. Deactivation is due to some growth of PdO crystallite revealed by Raman spectroscopy and still could not be detected by XRD.

Toluene catalytic combustion over copper modified Mn0.5Ce0.5 Ox solid solution sponge-like structures

Catalytic combustion is a well-established way to remove the pollution of volatile organic compounds (VOCs), and the highly active catalyst is the key issue of this process. Herein, a series of sponge-like ternary mixed oxide were prepared by a facile surfactant modified coprecipitation approach. The structure properties were characterized via BET, XRD, Raman, TEM, EDS, H2-TPR, and XPS techniques. It was found that the Cu content significantly influences the catalytic activity in toluene combustion. The CMC-2 (Cu:Mn:Ce=1:5:5) showed the best catalytic performance under the air atmosphere, and the complete conversion of toluene was achieved at 240°C. The characterization reveals that a proper amount of Cu facilitates the incorporation of highly reducible Mn4+ into ceria lattice to form sponge-like MnCeOx solid solution structures. Such promotion effect of copper can improve the redox behavior, produce large amounts of Oα at the interface of CuOx/MnCeOx, both of which benefit the toluene combustion at low temperature. The findings of this work highlight the importance of Cu in preparation of the active MnOx−CeO2 catalyst for VOCs combustion.

Selective catalytic combustion of hydrogen cyanide over metal modified zeolite catalysts: From experiment to theory

A series of metal modified zeolite including Cu-(Beta, FER, MCM-22, MCM-49, MOR) and M-(M=Cu, Co, Fe, Mn, Ni)-ZSM-5 was prepared by impregnation method and characterized by BET, XRD, and H2-TPR. HCN-SCC (selective catalytic combustion) activity measurement results suggest that Cu-ZSM-5 exhibiting excellent HCN conversion activity (T90=350°C) and N2 yield (>95% at T>350°C) constitutes one kind of promising candidate for HCN catalytic abatement. The HCN-SCC mechanism was further investigated by density functional theory (DFT) over constructed 20T-Cu-ZSM-5 models, which suggests that: (i) the 20T-Cu-ZSM-5 containing double active [Cu]+ site was much more favorable than that of 20T-Cu-ZSM-5 with single active [Cu]+ site during NCO generation step, being mainly related to the cooperation effect of double active [Cu]+ site; (ii) NCO+NO→N2+CO2 was confirmed to the one kind of probable reaction pathway for N2 and CO2 generations, wherein the NO could be produced through oxidation of NCO; (iii) the DFT energy calculation results as well as the microkinetic analyses suggested that the NCO formation step possessing the highest energy barrier (10.4kcalmol−1) was proposed to be the rate determining step of the whole catalytic cycle.

Catalytic Combustion of Soot Particulates over Rare Earth Pyrochlore Oxides Doped with Transition Metals

Catalytic combustion is an efficient way to remove soot particulates from automobile exhausts. A series of rare earth pyrochlore oxides La2Sn1.8TM0.2O7 (TM=Sn, Mn, Fe, Co, Cu) were prepared with CTAB-assisted sol-gel method. The products were characterized by XRD,N2 Adsorption-Desorption, SEM, FT-IR, H2-TPR and PL techniques. Their catalytic activity for soot oxidation was investigated by TPO under tight conditions in both O2 and NO+O2 atmospheres. After calcination at 900℃, the as-synthesized oxides with pure pyrochlore phase displayed nanospheres with diameter of 30-60 nm and relatively large surface areas. The partial substitution of Sn with transition metals largely influenced the reduction behavior of pyrochlores especially on the low temperature range in H2-TPR profiles, which was due to the interactions between Sn and transition metals. The improved oxygen mobility might be derived from the structure defects induced by transition metals doping, which could be helpful in oxidation reactions. In comparison with uncatalyzed reactions, the La2Sn2O7 catalyst exhibited modest catalytic activity for soot combustion, while transition metals incorporation further enhanced the activity and selectivity. The improved activity of transition metals doped samples was likely to be associated with the improved reducibility and increased surface oxygen vacancies on the pyrochlore oxides. The presence of NO in the gas phase significantly enhanced the soot oxidation activity, which was due to the promotion effect of NO2. Especially, the densities of active oxygen sites and turnover frequency (TOF) values of the catalysts, quantified by isothermal anaerobic titration with soot as a probe molecule, were used to explain the different soot combustion behaviors. Among the pyrochlore oxides, the Co-doped pyrochlore sample displayed the highest ignition activity and the largest intrinsic activity with TOF of 3.20×10-3 s-1.