Tight Contact Conditions Research Articles

The use of 18O2 to investigate the soot oxidation process on Co3O4, Co3O4-CeO2 and CeO2 catalysts in tight contact conditions

The use of 18O2 to investigate the soot oxidation process on Co3O4, Co3O4-CeO2 and CeO2 catalysts in tight contact conditions

Effect of oxygen vacancy and highly dispersed MnOx on soot combustion in cerium manganese catalyst

Cerium manganese bimetallic catalysts have become the focus of current research because of their excellent catalytic performance for soot combustion. Two series of cerium manganese catalysts (Na-free catalysts and Na-containing catalysts) were prepared by coprecipitation method and characterized using XRD, N2 adsorption–desorption, SEM, Raman, XPS, H2-TPR, O2-TPD, Soot-TPR-MS and in situ IR. The effects of abundant oxygen vacancies and surface highly dispersed MnOx on soot catalytic combustion of cerium manganese catalysts prepared by different precipitants were analyzed. The activity test results show that the active oxygen species released by a large number of oxygen vacancies in the cerium manganese catalyst are more favorable to the soot catalytic combustion than MnOx which is highly dispersed on the surface of the catalyst and has good redox performance at low temperature. Because the catalytic effect of MnOx on the surface of Na-free catalysts is more dependent on the contact condition between the catalyst and the soot, this phenomenon can be observed more easily under the loose contact condition than under the tight contact condition. The activity cycle test results show that these two series of catalysts show good stability and repeated use will hardly cause any deactivation of the catalysts.

Rational design of hierarchically micrometer scaled macro-mesoporous ceria-zirconia composites for enhancing diesel soot catalytic combustion performance

Diesel soot particulate is the primary source of urban atmospheric fine particulate matters (PM2.5), catalytic soot elimination on diesel participate filter is invariably an important yet challenging subject, because of the inherently poor solid-solid contact of soot-catalyst. In this study, we report a hierarchically porous ceria-zirconia composite with micrometer scaled macroporous structure, CZ-8, for enhancing catalyst-soot contact efficiency and soot catalytic combustion performance. Scanning electron microscope (SEM), N2 adsorption-desorption and mercury porosimetry results demonstrate that the CZ-8 catalyst has definite micrometer scaled macroporous (0.5–5.0 μm) and interconnected mesoporous (∼20 nm) structure. Raman and X-ray diffraction (XRD) results show that the dominant crystal structure of the CZ-8 is cubic fluorite and the relatively larger crystalline grain contribute to the macroporous structure construction. The filamentous diesel soot particulate (hundreds nanometers or even several micrometers) is difficult to enter the pores of the conventional mesoporous ceria-zirconia catalysts. Nonetheless, it can enter the micrometer scaled pores of the CZ-8 and hence improve the soot-catalyst contact efficiency, and oxygen can efficiently contact with soot-catalyst through the mesopores. Accordingly, the CZ-8 catalyst displays a significantly lower light-off temperature and better soot catalytic combustion performance under loose and tight contact conditions. Thus, this work suggests that enhancing solid(soot)-solid(catalyst)-gas(oxygen) contact efficiency by hierarchically porous structure with micrometer scaled macropores of catalyst is a promising new pathway for improving soot catalytic combustion performance and controlling diesel exhaust particulate emissions.

Facile and template-free synthesis of nano-macroporous LaCoO3 perovskite oxide for efficient diesel soot oxidation

The basic LaCoO3 perovskite oxides were prepared by the series of methods (reverse co-precipitation, citric acid aided sol–gel, glycine assisted solution combustion), underwent physicochemical characterization (XRD, FTIR, BET, XPS and SEM), followed by their soot oxidation activity tests in both “loose” and “tight” conditions of soot-catalyst contact. The activity tests revealed that the LaCoO3 catalyst formed using glycine assisted combustion synthesis gives the best performance with the T10, T50, and T90 at 361 °C, 404 °C and 445 °C, respectively, in loose contact conditions and T10, T50, and T90 at 306 °C, 330 °C and 355 °C, respectively, in tight contact conditions. Its outstanding performance can be attributed to its unique morphology consisting of scaffolds having an extensively interconnected macroporous network with macropores having nanoporous struts as walls as evidenced by SEM results. Such morphology makes the active sites of inner pores accessible to the gaseous (air) as well solid reactant (soot particles), thereby benefitting soot oxidation reaction. Supplementary InformationThe online version contains supplementary material available at 10.1007/s11144-022-02219-5.

High performance of K-supported Pr2Sn2O7 pyrochlore catalysts for soot oxidation

A highly active catalyst of K-supported Pr2Sn2O7 pyrochlore nanosphere (K/PrSn) was synthesized by impregnation method with K2CO3 as precursors for soot oxidation in this work. The catalysts were systematically characterized by XRD, SEM, FTIR, N2 adsorption–desorption, H2-TPR and soot-TPR techniques. Pure Pr2Sn2O7 exhibits uniform litchis-like spherical clusters morphology, composed of small nanoparticles of ∼ 30 nm in diameter. K species exist on K/PrSn catalysts surface in three forms: highly dispersed K2CO3, highly dispersed KO2 and bulk KO2. The catalyst containing 10 wt% of K (10 K/PrSn) showed the best catalytic performance and high stability in soot combustion under both tight and loose contact conditions. It can be speculated that potassium supporting plays crucial roles in K/PrSn catalyzed soot oxidation: (1) it improves the catalyst-soot contact by forming macroporous structure and/or due to the low-melting point of alkali metal, (2) it increases the surface basicity, which favors soot oxidation through formation of carbonate intermediates, (3) it enhances the reducibility of the catalyst due to the interaction between K and PrSn support, (4) K species itself may participate in the oxidation of soot particulates. Pr2Sn2O7 pyrochlore supported with high dispersion of potassium exhibits a superior reaction performance and good stability, which has the potential to be applied in some real diesel exhaust control processes.

Experimental Evaluation on the Catalytic Activity of a Novel CeZrK/rGO Nanocomposite for Soot Oxidation in Catalyzed Diesel Particulate Filter

A nanostructured solid solution catalyst CeZrK/rGO for soot oxidation in catalyzed diesel particulate filter was synthesized using the dipping method. The reduced graphene oxide (rGO) was used as the catalyst carrier, and CeO2, ZrO2, and K2O were mixed with the molar ratio of 5:1:1, 5:2:2 and 5:3:3, which were referred to as Ce5Zr1K1/rGO, Ce5Zr2K2/rGO, and Ce5Zr3K3/rGO, respectively. The structure, morphology and catalytic activity of the CeZrK/rGO nanocomposites were thoroughly investigated and the results show that the CeZrK/rGO nanocomposites have nanoscale pore structure (36.1–36.9 nm), high-dispersion quality, large specific surface area (117.2–152.4 m2/g), small crystallite size (6.7–8.3 nm), abundant oxygen vacancies and superior redox capacity. The 50% soot conversion temperatures of Ce5Zr1K1/rGO, Ce5Zr2K2/rGO, and Ce5Zr3K3/rGO under tight contact condition were decreased to 352 °C, 339 °C and 358 °C respectively. The high catalytic activity of CeZrK/rGO nanocomposites can be ascribed to the following factors: the doping of Zr and K ions causes the nanocrystalline phase formation in CeZrK solid solutions, reduces the crystallite size, generates abundant oxygen vacancies and improves redox capacity; the rGO as a carrier provides a large specific surface area, thereby improving the contact between soot and catalyst.

Enhancement effect of oxygen mobility over Ce0.5Zr0.5O2 catalysts doped by multivalent metal oxides for soot combustion

Ce0.5Zr0.5O2 catalysts promoted by multivalent transition metal (Mn, Fe, Co) oxides have been prepared for accelerating soot combustion. Compared with Ce0.5Zr0.5O2 catalyst, Mn- and Co-doped catalysts remarkably improved the catalytic activity of soot combustion, while the Fe-doped catalyst had a slightly effect on soot combustion. TEM, N2 adsorption-desorption isotherms and XRD were testified to find the correlation between catalytic activity and texture properties, the results revealed that texture properties of prepared catalysts were not sensitive to catalytic activity. However, the more active oxygen species and superior mobility of lattice oxygen species with more oxygen vacancies characterized by XPS, H2-TPR and O2-TPD were proved as significant roles on soot combustion after incorporation of various multivalent metals, especially for Mn and Co. Furthermore, Co-doped catalyst with the excellent NO-NO2 conversion capacity visibly reduced soot ignition temperature in 600 ppm NO + 10% O2 + N2 under tight contact and loose contact condition due to NO2 is a more effective oxidizing agent than O2. On the contrary, Fe-doped catalyst with slightly better redox performance and more oxygen vacancies reflected weaker NO oxidation performance than support that might be the reason of abundant adsorbed carbonates inhibiting further adsorption of NO and active oxygen species, which also led to the invisible promoting effect of soot combustion.

Catalytic Soot Oxidation Activity of NiO-CeO2 Catalysts Prepared by a Coprecipitation Method: Influence of the Preparation pH on the Catalytic Performance.

A series of NiO–CeO2 mixed oxide catalysts have been synthesized by a modified coprecipitation method at three different pH values (pH = 8, 9, and 10). The NiO–CeO2 mixed oxide samples were characterized by TGA, XRD, inductively coupled plasma atomic emission spectroscopy (ICP-AES), FTIR, Brunauer–Emmett–Teller (BET) surface area, H2 temperature-programmed reduction (H2-TPR), and electron microscopy (high-angle annular dark-field transmission electron microscopy/energy-dispersive X-ray spectroscopy (HAADF-TEM/EDS)). The catalytic activities of the samples for soot oxidation were investigated under loose and tight contact conditions. The catalysts exhibited a high BET surface area with average crystal sizes that varied with the pH values. Electron microscopy results showed the formation of small crystallites (~5 nm) of CeO2 supported on large plate-shaped particles of NiO (~20 nm thick). XRD showed that a proportion of the Ni2+ was incorporated into the ceria network, and it appeared that the amount on Ni2+ that replaced Ce4+ was higher when the synthesis of the mixed oxides was carried out at a lower pH. Among the synthesized catalysts, Ni-Ce-8 (pH = 8) exhibited the best catalytic performance.

Factors determining gasoline soot abatement over CeO2–ZrO2-MnOx catalysts under low oxygen concentration condition

Soot oxidation under a low concentration O2 (0.5% O2/N2) was investigated using CeO2–ZrO2-MnOx mixed oxides with varied amounts of MnOx, in order to gain low temperature catalytic activity and find out the main factors affecting the soot oxidation. The catalytic activity was remarkably improved over these catalysts compared to that of non-catalyst in such a low concentration of O2. In particular, CeO2–ZrO2-MnOx with 10% MnOx doping (M10-CZ) showed the highest catalytic activity with its T50 values of 340 °C under tight contact condition. The results of N2 adsorption-desorption and X-ray diffraction (XRD) indicated that the textural and structural properties were not positive correlation with soot oxidation, are not the main factors affecting the catalytic activity of CeO2–ZrO2 and CeO2–ZrO2-MnOx catalysts. The results of oxygen storage capacity (OSC), hydrogen-temperature programmed reduction (H2-TPR), O2 temperature program desorption (O2-TPD), UV Raman spectroscopy (UV Raman) and X-ray photoelectron spectroscopy (XPS) testified that redox ability, oxygen storage capacity, oxygen desorption capacity at low temperature and surface active oxygen species are more important for soot oxidation. The enhancements of the catalytic behavior after MnOx addition can be due to the improving of the adsorbed, activation and mobility of reactive oxygen species. In this work, these factors about generation and movement of reactive oxygen species are crucial for soot oxidation in a low oxygen concentration condition.

Lattice oxygen activity in ceria-praseodymia mixed oxides for soot oxidation in catalysed Gasoline Particle Filters

Two series of ceria-praseodymia catalysts with varying composition have been systematically investigated in the oxidation of soot under inert atmosphere in order to find out its potential utilization in Gasoline Particulate Filters for GDI engines. The samples have been widely characterized by XRD, Raman spectroscopy, TEM, FESEM, XPS, N2 adsorption at −196 °C and O2-TPD. The praseodymium incorporation onto the ceria enhances the oxygen mobility in the subsurface/bulk of the sample favoring higher O2 released amounts under inert atmosphere. The intermediate compositions can promote more accentuated O2 emissions at moderate temperatures (up to 500 °C). The efficiency of the own active oxygen species released from the catalyst to oxidize soot under inert atmosphere, even under loose contact mode, has been well demonstrated. The pathways of the mechanism taking place seem to be dependent on the temperature and mainly on the type of contact among soot and catalyst. Under loose contact conditions and low-medium temperatures, the O2 freshly emitted from the catalyst can oxidize soot more efficiently than a diluted O2-gas stream. Conversely, under more severe conditions (higher temperature or tight contact conditions), the soot acts as a “driving force” and the own lattice oxygen species can be transferred directly towards soot surface in an efficient way.

Flower-like Mn3O4/CeO2 microspheres as an efficient catalyst for diesel soot and CO oxidation: Synergistic effects for enhanced catalytic performance

Synergistic composite metal oxides are proven to be impressive materials due to their multi-functionalities across various catalytic applications. In a composite metal oxide, the interfacial chemistry between the components could provide exceptional redox and catalytic properties. In the present manuscript, the fundamental focus is devoted to investigating the interactions between active metal oxides at their interfaces and the catalytic activities towards diesel soot and CO oxidation. A series of flower-like microspheres namely, CeO2, 10%Mn3O4/CeO2, 20%Mn3O4/CeO2, and 40%Mn3O4/CeO2 catalysts were synthesized, where the effect of different Mn3O4 loadings towards soot combustion and CO oxidation were investigated. The characteristic 50% conversion temperature (T50) of catalytic soot oxidation under loose and tight contact conditions for CeO2 microspheres are 502 and 484 °C, respectively. After the integration of Mn3O4 and CeO2, the T50 values were decreased with the lowest values observed for the 20%Mn3O4/CeO2 microspheres (381 and 350 °C). Similarly, 20%Mn3O4/CeO2 microspheres showed T50 value at 103 °C for CO oxidation when compared to pure CeO2 microspheres (216 °C) and Mn3O4 nanoparticles (356 °C). Activation energy values were decreased when the Mn3O4/CeO2 composite used in soot and CO oxidation. The high catalytic activity can be attributed to the strong synergistic interactions between CeO2 and Mn3O4, variable oxidation states, the amount of readily available surface redox active sites and oxygen vacancies. The possible interfacial interaction between CeO2 and Mn3O4 can be exploited to exhibit enhanced surface structural, and redox properties when compared to the pure counterparts. Post-catalytic oxidation analysis confirms the high stability of the Mn3O4/CeO2 composite. The present study points out the vital role of interfacial interactions in composite metal oxides for improving the surface and redox properties, which are important for the development of highly efficient soot and CO oxidation catalysts.

Experimental study on fundamental effect of H2 for catalytic soot oxidation with Pt/CeO2 using a flow reactor system

The effect of hydrogen on catalytic soot oxidation was investigated to find new conditions for lowering the regeneration temperature in catalyzed diesel particulate filtration with hydrogen. Soot oxidation experiments using a flow reactor with a Pt/CeO2 catalyst were carried out to represent catalyzed diesel particulate filtration. Under conditions using more than 6% hydrogen with water, the soot oxidation by hydrogen started at 155 °C for loose contact conditions and at 175 °C for tight contact conditions. The soot oxidation rate tended to increase with increasing concentrations of hydrogen and oxygen. In contrast, no difference was observed with various water concentrations. The HO2 generated during hydrogen oxidation oxidized soot at low temperature. The soot oxidation temperature of 155 °C was lower than the regeneration temperature in catalyzed diesel particulate filtration reported previously.

Catalytic Oxidation of Soot on a Novel Active Ca-Co Dually-Doped Lanthanum Tin Pyrochlore Oxide.

A novel active Ca-Co dually-doping pyrochlore oxide La2−xCaxSn2−yCoyO7 catalyst was synthesized by the sol-gel method for catalytic oxidation of soot particulates. The microstructure, atomic valence, reduction, and adsorption performance were investigated by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), H2-TPR (temperature-programmed reduction), and in situ diffuse reflection infrared Fourier transformed (DRIFTS) techniques. Temperature programmed oxidation (TPO) tests were performed with the mixture of soot-catalyst under tight contact conditions to evaluate the catalytic activity for soot combustion. Synergetic effect between Ca and Co improved the structure and redox properties of the solids, increased the surface oxygen vacancies, and provided a suitable electropositivity for oxide, directly resulting in the decreased ignition temperature for catalyzed soot oxidation as low as 317 °C. The presence of NO in O2 further promoted soot oxidation over the catalysts with the ignition temperature decreased to about 300 °C. The DRIFTS results reveal that decomposition of less stable surface nitrites may account for NO2 formation in the ignition period of soot combustion, which thus participate in the auxiliary combustion process.

Heterostructured Copper-Ceria and Iron-Ceria Nanorods: Role of Morphology, Redox, and Acid Properties in Catalytic Diesel Soot Combustion.

This work reports the synthesis of heterostructured copper-ceria and iron-ceria nanorods and the role of their morphology, redox, and acid properties in catalytic diesel soot combustion. Microscopy images show the presence of nanocrystalline CuO (9.5 ± 0.5 nm) and Fe2O3 (7.3 ± 0.5 nm) particles on the surface of CeO2 nanorods (diameter is 8.5 ± 2 nm and length within 16-89 nm). In addition to diffraction peaks of CuO and Fe2O3 nanocrystallites, X-ray diffraction (XRD) studies reveal doping of Cu2+ and Fe3+ ions into the fluorite lattice of CeO2, hence abundant oxygen vacancies in the Cu/CeO2 and Fe/CeO2 nanorods, as evidenced by Raman spectroscopy studies. XRD and Raman spectroscopy studies further show substantial perturbations in Cu/CeO2 rods, resulting in an improved reducibility of bulk cerium oxide and formation of abundant Lewis acid sites, as investigated by H2-temperature-programmed reduction and pyridine-adsorbed Fourier transform infrared studies, respectively. The Cu/CeO2 rods catalyze the soot oxidation reaction at the lowest temperatures under both tight contact (Cu/CeO2; T50 = 358 °C, temperature at which 50% soot conversion is achieved, followed by Fe/CeO2; T50 = 368 °C and CeO2; T50 = 433 °C) and loose contact conditions (Cu/CeO2; T50 = 419 °C and Fe/CeO2; T50 = 435 °C). A possible mechanism based on the synergetic effect of redox and acid properties of Cu/CeO2 nanorods was proposed: acid sites can activate soot particles to form reactive carbon species, which are oxidized by gaseous oxygen/lattice oxygen activated in the oxygen vacancies (redox sites) of ceria rods.

Thermally stable α-alumina supported ceria for coking resistance and oxidation of radical coke generated in-situ

A series of thermally stable α-alumina supported and unsupported ceria catalysts with varying composition is systematically investigated under realistic coke – catalyst contact conditions for the oxidation of in-situ generated coke during ethylene pyrolysis. These catalysts have been designed for use in high temperature applications of steam cracking. The textural and structural characterization of α-alumina supported ceria catalysts show the absence of solid oxide solutions, with the supported catalysts having distinct ceria domains on the alumina support. For comparison, two types of coke – catalyst contacting are explored: (i) tight contact by grinding industrial coke with catalyst and (ii) realistic in-situ contact, where coke is deposited on the catalytic support. During in-situ coke deposition, ceria-containing catalysts demonstrate resistance to coking as compared to the bare α-alumina support. Ceria and ceria – alumina composites also enabled coke oxidation at lower temperatures than the un-catalyzed coke oxidation. The presence of both Ce3+ and Ce4+ is confirmed by X-ray absorption near edge structure (XANES), consistent with the well-known redox capability of ceria catalysts. Kinetic studies revealed 50–80 mol% Ce as the best compositions for oxidation activity towards both industrial and in-situ coke. The catalytic activity correlates with the presence of reactive lattice oxygen atoms on ceria for both types of contact, indicating a similar mechanism of carbon oxidation under in-situ contact and tight contact conditions. A mechanism of reaction involving lattice oxygen of ceria is proposed for the oxidation of coke as well as for retardation of coke deposition on ceria domains.

Effect of Cs-Ce-Zr Catalysts/Soot Contact Conditions on Diesel Soot Oxidation.

Cs–Ce–Zr catalysts with various weight ratios are prepared by the sol–gel method in this paper. The main crystalline phases were identified by X-ray diffraction. The activities of catalysts during soot combustion were tested by thermogravimetric and differential scanning calorimetry. The contact conditions of soot/catalysts (sintered at 450 and 380 °C, respectively, under loose and tight contact conditions) were observed by scanning electron microscopy to study the effect of contact conditions on catalytic activity, and it was determined that the catalytic activities under tight contact conditions are superior to those under loose contact conditions. However, the soot oxidation rate speeds up after the peak temperature of about 450 °C under loose contact conditions, which is due to the fact that the contact condition is enhanced by melting CsNO3. The soot onset ignition temperature is lower for the catalysts with more Cs content under loose contact conditions. The minimum gaps of the soot onset ignition temperature and soot oxidation rates under the two contact conditions are 32 and 7 °C, which shows that the gap of catalytic activities under the respective contact conditions can be decreased by the formation of different crystalline phases.

Nanowire Morphology of Mono- and Bidoped α-MnO2 Catalysts for Remarkable Enhancement in Soot Oxidation.

In the present work, nanowire morphologies of α-MnO2, cobalt monodoped α-MnO2, Cu and Co bidoped α-MnO2, and Ni and Co bidoped α-MnO2 samples were prepared by a facile hydrothermal synthesis. The structural, morphological, surface, and redox properties of all the as-prepared samples were investigated by various characterization techniques, namely, scanning electron microscopy (SEM), transmission and high resolution electron microscopy (TEM and HR-TEM), powder X-ray diffraction (XRD), N2 sorption surface area measurements, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature-programmed reduction (H2-TPR), and oxygen-temperature-programmed desorption (O2-TPD). The soot oxidation performance was found to be significantly improved via metal mono- and bidoping. In particular, Cu and Co bidoped α-MnO2 nanowires showed a remarkable improvement in soot oxidation performance, with its T50 (50% soot conversion) values of 279 and 431 °C under tight and loose contact conditions, respectively. The soot combustion activation energy for the Cu and Co bidoped MnO2 nanowires is 121 kJ/mol. The increased oxygen vacancies, greater number of active sites, facile redox behavior, and strong synergistic interaction were the key factors for the excellent catalytic activity. The longevity of Cu and Co bidoped α-MnO2 nanowires was analyzed, and it was found that the Cu/Co bidoped α-MnO2 nanowires were highly stable after five successive cycles and showed an insignificant decrease in soot oxidation activity. Furthermore, the HR-TEM analysis of a spent catalyst after five cycles indicated that the (310) crystal plane of α-MnO2 interacts with the soot particles; therefore, we can assume that more-reactive exposed surfaces positively affect the reaction of soot oxidation. Thus, the Cu and Co bidoped α-MnO2 nanowires provide promise as a highly effective alternative to precious metal based automotive catalysts.

Catalytic reactions of coke with dioxygen and steam over alkaline-earth-metal-doped cerium-zirconium mixed oxides

A series of cerium-zirconium mixed oxides doped with alkaline earth metals was prepared by calcining a mixture of Ce0.8Zr0.2O2 and the nitrate salt of alkaline earth metals at 1173K. The results from X-ray diffraction, Raman spectroscopy and analytical electron microscopy indicated the alkaline earth compounds were dispersed on the surface of Ce0.8Zr0.2O2. The doped mixed oxides were evaluated in the catalytic reaction of solid coke under tight contact conditions with 10 vol.% O2 in He at 693K and with 100vol.% H2O at 993K using thermogravimetric analysis. For coke oxidation with O2, the weight loss was first order in coke, and the measured first order rate constant was proportional to the total surface area of catalyst at low catalyst loadings. For coke gasification with H2O, the weight loss was nearly zero order in coke, and the measured areal reaction rate was independent of the total surface area of catalyst at low catalyst loadings. The addition of alkaline earth metals inhibited coke oxidation with dioxygen but promoted coke gasification with steam.

Enhanced Catalytic Performance of Manganese and Cobalt Co–doped CeO2 Catalysts for Diesel Soot Oxidation

AbstractNanosized manganese and cobalt codoped ceria (Ce0.8Mn0.1Co0.1O2−δ) solid solutions have been prepared through simple coprecipitation method to study the effect of Mn and Co bi‐dopants towards diesel soot oxidation. Pure ceria (CeO2), manganese doped ceria (Ce0.8Mn0.2O2−δ), and cobalt doped ceria (Ce0.8Co0.2O2−δ) solid solutions have also been prepared for comparison. XRD results revealed the formation of solid solutions in doped samples. XPS results confirmed the presence of more Ce3+ ions and surface adsorbed oxygen in codoped ceria. H2‐TPR study disclosed that the codoping of ceria exceptionally improves the redox behaviour of CeO2. The catalytic activity results demonstrate that Ce0.8Mn0.1Co0.1O2−δ shows much better activity (T50 ∼ 636 K) while compared to pure CeO2 (T50 ∼ 874 K) in tight contact conditions. A larger surface area, facile redox behaviour, and high concentration of surface adsorbed oxygen species are proposed to be the crucial factors for the enhanced catalytic activity.

Soot Combustion over Nanostructured Ceria with Different Morphologies.

In this study, nano-structure ceria with three different morphologies (nanorod, nanoparticle and flake) have been prepared by hydrothermal and solvothermal methods. The ceria samples were deeply characterized by XRD, SEM, TEM, H2-TPR, XPS and in-situ DRIFTS, and tested for soot combustion in absence/presence NO atmospheres under loose and tight contact conditions. The prepared ceria samples exhibit excellent catalytic activities, especially, the CeO2 with nanorod (Ce-R) shows the best catalytic activity, for which the peak temperature of soot combustion (Tm) is about 500 and 368 °C in loose and tight contact conditions, respectively. The catalytic activity for Ce-R is higher than that of the reported CeO2 catalysts and reaches a level that of precious metals. The characterization results reveal that the maximal amounts of adsorbed oxygen species on the surface of the nanostructure Ce-R catalyst should be the crucial role to decide the catalytic soot performance. High BET surface area may also be a positive effect on soot oxidation activity under loose contact conditions.