Soot Oxidation Performance Research Articles

Catalytic performance of supported Ag nano-particles prepared by liquid phase chemical reduction for soot oxidation

The effect of size and morphology of Ag catalysts supported on ZrO2 on the soot oxidation activity was investigated. Spherically shaped Ag nano-particles with the size of ca. 16nm, prepared by liquid-phase chemical reduction, supported on ZrO2 (Ag/ZrO2(NP)) exhibited outstanding performance for soot oxidation with gaseous O2 in tight and loose contact modes, compared with hemispherically shaped Ag particles prepared by impregnation (Ag/ZrO2(IMP)). The exceptional performance of Ag/ZrO2(NP) for soot oxidation in loose contact mode was explained by relatively good catalyst-soot contact state and effective migration of active oxygen species from the catalyst to soot. In addition to morphological effect, Ag nano-particles supported on ZrO2 were found to be stabilized in the surface valence state of Ag+, and then oxygen species participating in soot oxidation can be effectively activated on Ag+ sites. We concluded that the presence of Ag+ sites on the surface of Ag nano-particles is responsible for high soot oxidation activity.

Effects of Synthesis Routes on the States and Catalytic Performance of Manganese Oxides Used for Diesel Soot Combustion

The catalyst obtained through the co-precipitation of Mn(Ac)(2) and (NH4)(2)CO3 (denoted as Mn-Ac-NH4) displays the highest performance for soot oxidation. Compared with other MnOx catalysts, the catalyst Mn-Ac-NH4 exhibits much better reducibility and more uniform sponge-like nanostructure. The characterization results indicate that the oxygen species on the surface of Mn-Ac-NH4 are more active for soot combustion. The NO species can also be captured and oxidized by these oxygen species, generating more reactive NO2 which can enhance soot oxidation.

112 ディーゼルパティキュレートフィルタのすす酸化性能に及ぼす触媒担持方法の影響評価

112 ディーゼルパティキュレートフィルタのすす酸化性能に及ぼす触媒担持方法の影響評価

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.

In situ investigation of Diesel soot combustion over an AgMnOx catalyst

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

A mechanistic study on soot oxidation over CeO 2–Ag catalyst with ‘rice-ball’ morphology

A CeO 2–Ag catalyst with a ‘rice-ball’ morphology, consisting of Ag particles in the center surrounded by fine CeO 2 particles, exhibits exceptional catalytic performance for soot oxidation by O 2 below 300 °C. The reaction mechanism over this catalyst was studied by O 2 temperature-programmed desorption (O 2-TPD), 18O/ 16O isotopic exchange (IE) reaction, and electron spin resonance (ESR) techniques. It is speculated that adsorbed oxygen species on the Ag surface migrate to the CeO 2 surface via the Ag/CeO 2 interface to form O n x - species (at least partly O 2 - ) and further migrate onto the soot particles. Due to morphological compatibility of the moderately large Ag particles (ca. 30–40 nm) and the extremely large interfacial area with the CeO 2 particles, the formation and migration rates of the oxygen species on the CeO 2–Ag catalyst are efficiently promoted, resulting in its distinguished catalytic performance and relative insensitivity to the contact mode of the soot–catalyst mixture.

Different valent ions-doped cerium oxides and their catalytic performances for soot oxidation

The nmCeO 2 and Ce 0.8M 0.2O 2 (M = Sm, Zr, V) nanoparticles were prepared by the method of microwave-assisted heating decomposition. Their catalytic performances for diesel soot oxidation were investigated with temperature-programmed oxidation reaction (TPO). Spectroscopic techniques (XRD, Raman, UV-Vis DRS and FT-IR) were utilized to characterize the structures of nmCeO 2 and Ce 0.8M 0.2O 2 catalysts. The results show that the structures of the catalysts depend on the different doped ions. Ce 0.8Sm 0.2O 2 and Ce 0.8Zr 0.2O 2 still preserved a face-centered cubic fluorite structure of CeO 2. However, CeVO 4 crystallite was formed as V doping (Ce 0.8V 0.2O 2). Nanometer CeO 2, Ce 0.8Sm 0.2O 2 and Ce 0.8Zr 0.2O 2 exhibited higher catalytic activity than conventional CeO 2 and Ce 0.8V 0.2O 2 for soot combustion due to the nanometer effect and the good contact between the catalyst and soot. For soot oxidation, nmCeO 2 is mainly active components. However, the doping of Sm or Zr could remarkably improve the thermal stability of nmCeO 2, and the doping of Sm or V could enhance the ability to resist SO 2 poison of catalysts.

Comparison of Preparation Methods of Copper Based PGMFree Diesel-Soot Oxidation Catalysts

CuO-CeO2 systems have been proposed as a promising catalyst for low temperature diesel-soot oxidation. CuO-CeO2 catalysts prepared by various methods were examined for air oxidation of the soot in a semi batch tubular flow reactor. The air oxidation of soot was carried out under tight contact with soot/catalyst ratio of 1/10. Air flow rate was 150 ml/min, soot-catalyst mixture was 110 mg, heating rate was 5 0C/min. Prepared catalysts were calcined at 500 0C and their stability was examined by further heating to 800 0C for 4 hours. It was found that the selectivity of all the catalysts was nearly 100% to CO2 production. It was observed that the activity and stability of the catalysts greatly influenced by the preparation methods. The strong interaction between CuO and CeO2 is closely related to the preparation route that plays a crucial role in the soot oxidation over the CuO-CeO2 catalysts. The ranking order of the preparation methods of the catalysts in the soot oxidation performance is as follows: sol-gel > urea nitrate combustion > Urea gelation method > thermal decomposition > co-precipitation. © 2011 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Catalytic performance of supported precious metal catalysts for the combustion of diesel particulate matter

CeO 2 and TiO 2 supported precious metal (Ag, Pt and Pd) catalysts were prepared by an impregnation method, and their catalytic performance for oxidation of simulated diesel particulate matter (PM) was investigated by thermogravimetry (TG), differential thermal analysis (DTA) and mass spectrometry (MS) under both tight-contact (TC) and loose-contact (LC) conditions. The simulated PM was prepared by liquid-phase adsorption of SOF (eicosane, C 20H 42) on soot (carbon black). Catalytic performance for the oxidation of simulated PM depended on both metal species and supports. CeO 2 was inherently active for both SOF and soot oxidation, and TiO 2 was nearly inactive. Pt was the most active species for SOF oxidation, followed by Pd and Ag. The SOF oxidation was independent of contact condition between the simulated PM and catalysts. Soot oxidation performance, on the other hand, drastically affected by the contact conditions, and Ag was far more active than Pt and Pd under both TC and LC conditions. Ag/CeO 2 was the most active soot oxidation catalyst. The oxidation of soot was influenced by the coexisting SOF depending on catalytic materials and contact modes.

Highly Active Catalysts of Gold Nanoparticles Supported on Three‐Dimensionally Ordered Macroporous LaFeO3 for Soot Oxidation

The catalyst support 3DOM LaFeO3 contains highly ordered macropores that are connected with each other by small windows. 3DOM LaFeO3 supported gold catalysts, which combine the advantages of good contact by the macroporous support and highly active sites for activation of O2 by gold clusters, exhibit super catalytic performance for soot oxidation.

Three-dimensionally ordered macroporous Ce0.8Zr0.2O2-supported gold nanoparticles: synthesis with controllable size and super-catalytic performance for soot oxidation

A series of catalysts of three-dimensionally ordered macroporous (3DOM) Ce0.8Zr0.2O2-supported gold nanoparticles with controllable sizes were successfully synthesized by the facile method of gas bubbling-assisted membrane reduction (GBMR). All the catalysts possess well-defined 3DOM structures, which consist of interconnected networks of spherical voids, and the Au nanoparticles are well dispersed and supported on the inner wall of the uniform macropore. The relationship between Au particle sizes and the ability to adsorb and activate oxygen was characterized by means of O2-TPD and XPS. The results show that the active oxygen species (O−) and gold ions with oxidation state of Au+ are essential for soot oxidation reaction. 3DOM Au0.04/Ce0.8Zr0.2O2catalyst with Au particle size of 2–3 nm has the strong capability of adsorption and activation of oxygen. Thus, it exhibits super-catalytic activity for diesel soot oxidation, especially at low temperature. The reaction pathways of catalytic soot oxidation in the presence or absence of NO can be outlined as follows: at low temperature ( 250 °C), the catalytic activity is strongly related to the NO gas, because NO2 derived from NO oxidation is used as intermediate to catalyze soot oxidation.

Preparation, characterisation and catalytic performance for soot oxidation of copper-containing ZnAl 2O 4 spinels

Copper-containing ZnAl 2O 4 catalysts have been properly prepared by the glycothermal method, with copper loaded within the mixed oxide structure (catalyst Zn 0.95Cu 0.05Al 2O 4) or impregnated in the previously prepared support ZnAl 2O 4 (catalyst 5%Cu/ZnAl 2O 4). The samples were characterised by XRD, HRTEM, SEM-EDAX, N 2 adsorption at −196 °C, FT-IR, and H 2-TPR, and the catalytic combustion of soot under NOx/O 2 was tested. The mixed oxides, with confirmed spinel structure, consist of nanoparticles with around 5–12 nm. The impregnated catalyst is more active for soot combustion than both the bare support and the substituted catalyst, which is attributed to the proper reducibility of copper that catalyses the NO oxidation to NO 2. This catalyst is also highly selective towards CO 2 formation as soot combustion product.

Microwave improvement of catalyst performance in soot oxidation without additives

The application of microwaves allows to overcome technical hitches related to the regeneration of soot-filters allowing to perform it independently on the engine operating conditions. The performance of a SiC foam filter during microwave regeneration was investigated with and without a catalyst coating. The regeneration efficiency and the energy required for regeneration were evaluated for catalytic and uncatalytic SiC foams by varying the operating conditions of soot trapping.Results showed that for both catalytic foams, Fe/V/K and Cu/V/K, the capability to be heated independently of the amount of soot allows to maintain temperature sufficiently high to perform a complete foam filter regeneration. Moreover, the microwave absorbing properties of the catalytic phases allow to perform regeneration with a lower energy consumption with respect to the uncatalytic case. The presence of a catalyst also allows to overcome the dependence of microwave-assisted regeneration process on the operating conditions of soot loading.

Promotional effect of rare earths and transition metals in the combustion of diesel soot over CeO 2 and CeO 2–ZrO 2

The soot combustion behavior and the textural and structural characteristics of CeO 2 and a series of ceria-modified materials have been studied. It is shown that ceria doped with transition metals (Zr and Fe) and rare earth elements (La, Pr, Sm, Tb) results in more active catalysts with enhanced textural properties. ZrO 2 enhances the thermal stability and the oxygen storage capacity of pure ceria, resulting in better performance in soot oxidation. Remarkably, cerium–zirconium solid solution doped with rare earth does not achieve lower temperature of combustion, providing performances comparable to CeO 2 and CeO 2–ZrO 2. Cerium doped with Fe 2O 3 presents the better results as far as fresh samples are taken into account, but suffers from a net loss of activity after calcination. TGA experiments under N 2 atmosphere have confirmed the key role of oxygen storage capacity in soot oxidation.