Soot-catalyst Contact Research Articles

The effect of deposit morphology on soot oxidation in non-catalytic and catalytic processes

Investigating the oxidation behavior of soot particles with varying deposit morphologies is crucial for understanding the mechanisms behind uneven regeneration in diesel particulate filters and enhancing regeneration strategies. This study explores the impact of two distinct deposit morphologies on soot oxidation within non-catalytic and catalytic processes, with a particular focus on the associated changes in pore structure during oxidation. Findings indicate a minimal difference in oxidation activity between loose and compacted soot particles in non-catalytic oxidation, while a significant enhancement in oxidation activity is observed for compacted soot particles during catalytic oxidation. Specifically, compacted soot particles exhibit a pronounced reduction in total pore volume, particularly in macropores, and a shift in pore size distribution towards smaller diameters during non-catalytic oxidation. In the catalytic oxidation process, compacted soot particles predominantly form 2–10 nm mesopores, with limited formation of pores larger than 10 nm. Oxidation activity in the non-catalytic process positively correlates with pore volume, especially for 100–200 nm macropores. In contrast, during catalytic oxidation, oxidation activity inversely relates to pore volume, emphasizing the critical role of catalyst-soot contact in catalytic oxidation efficiency.

Influence of Co-Ni interactions on catalytic activity of xCo/NiO nanosheet catalysts in situ grown on monolithic cordierite for soot combustion

Co3O4-loaded NiO monolithic catalysts were successfully prepared on cordierite substrates using a simple hydrothermal and impregnation method. The mass transfer of gaseous reactants and products during soot combustion is facilitated by the constructed macroporous voids, thereby enhancing the soot-catalyst contact efficiency. The results demonstrate that the interaction of Ni and Co (Co2+ + Ni3+ ↔ Ni2+ + Co3+) leads to an increase in the amount of Co3+ cations, resulting in a higher quantity of oxygen vacancies. Besides the surface adsorbed oxygen (Oads), it demonstrates that the hydroxyl group (-OH) also acts as active oxygen species in soot oxidation. And, the impact of Co loading on the catalysts displays a volcano-type on the performance of soot oxidation. 0.5Co/NiO with the strongest CO-Ni interaction possesses the highest intrinsic activity. As a result, 0.5Co/NiO shows the highest activity with T50 at 382 °C in 600 ppm NO/10 % O2/N2 flow, as well as high stability and water resistance. Moreover, the prepared catalysts can efficiently catalyze NO to NO2, which possesses higher reactivity for soot oxidation than O2 and NO. Consequently, the as-designed Co/NiO monolithic catalysts hold great potential for applications in soot combustion and other non-homogeneous catalytic systems.

Cerium Doping Effect in 3DOM Perovskite-Type La2−xCexCoNiO6 Catalysts for Boosting Soot Oxidation

Herein, we present an in-depth investigation into the enhancement of catalytic soot oxidation through cerium-doped three-dimensional ordered macroporous (3DOM) La-Co-Ni-based perovskites synthesized with the colloidal crystal template (CCT) method. The 3DOM structure significantly contributes to the accessibility and interaction efficiency between soot and catalyst. Based on the results of powder X-ray diffraction (XRD), N2 adsorption-desorption measurements, scanning electron microscopy (SEM), temperature-programmed oxidation of NO (NO-TPO), temperature-programmed reduction of H2 (H2-TPR), in situ infrared Fourier transform spectroscopy (In-situ DRIFTS), and temperature-programmed oxidation (TPO) reactions, the role of cerium doping in modifying the structural and catalytic properties of 3DOM perovskite-type La2−xCexCoNiO6 catalysts was investigated systematically. The optimized cerium doping ratio in La2−xCexCoNiO6 catalysts can improve the microenvironment for efficient soot-catalyst contact, enhancing the catalytic activity of soot oxidation. Among the catalysts, the 3DOM La0.8Ce1.2CoNiO6 catalyst shows the highest catalytic activity for soot oxidation, whose T10, T50, and T90 values are 306 °C, 356 °C, and 402 °C, respectively. The mechanism of the cerium doping effect for boosting soot oxidation is proposed: The doping of Ce ions can increase the surface oxygen species, which is the main active species for promoting the key step of NO oxidation to NO2 in catalyzing soot oxidation. This research provides a new strategy to develop high-efficient non-noble metal catalysts for soot oxidation in pollution control and sustainable environmental practices.

PGM-free metal oxide nanoarray forests for water-promoted low-temperature soot oxidation

In this study, PGM free metal oxide based nanorod array (nanoarray) forests have been conformally integrated onto the millimeter-sized channel walls and microscale pores of SiC diesel particulate filter (DPF) substrates using scalable microwave-assisted hydrothermal and dip-coating methods. High-efficiency and robust low temperature soot oxidation is successfully achieved using such a new type of cDPFs as a result of i) promoted tight soot-catalyst contact through spontaneous soot deposits in-between nanorods, ii) highly dispersed loading of LaSrCoO3 perovskite oxidation catalysts onto ZnO nanorod arrays, effectively mitigating active site blockage by soot deposition. The light-off temperature of soot oxidation was lowered to 250 °C in oxygen, a 250 °C decrease compared to that of the commercial Pt based catalyst, due to the abundant oxygen vacancies enabled by the LaSrCoO3/ZnO (LSCO/ZnO) nanorod array catalysts. The performance of the catalyst was further enhanced to initiate the soot oxidation at ∼150 °C with co-fed gas of NO, due to the LSCO catalyzed NO2 formation and its favorable oxidation with soot at low temperature. Furthermore, the nanoarray supported perovskite catalyst shows excellent stability and activity after 120 h of hydrothermal aging at 650 °C. Soot oxidation Tmax is lowered from 542 °C to 510 °C under 6 % water steam condition due to the formation and promotion effect of oxidative -OH species. In situ DRIFTS study reveals that such -OH species form at various catalyst surfaces and interfaces, pointing to a potentially generic water promotion effect for solid/solid interfacial catalytic oxidation under humidity condition. Finally, the mechanistic soot oxidation pathways under O2, NO2, and H2O feeds are proposed for understanding the low-temperature soot oxidation behaviors over the nanoarray supported perovskite catalysts.

Electrospun Ce–Mn oxide as an efficient catalyst for soot combustion: Ce–Mn synergy, soot-catalyst contact, and catalytic oxidation mechanism

Increasing the contact efficiency and improving the intrinsic activity are two effective strategies to obtain efficient catalysts for soot combustion. Herein, the electrospinning method is used to synthesize fiber-like Ce–Mn oxide with a strong synergistic effect. The slow combustion of PVP in precursors and highly soluble manganese acetate in spinning solution facilitates the formation of fibrous Ce–Mn oxides. The fluid simulation clearly indicates that the slender and uniform fibers provide more interwoven macropores to capture soot particles than the cubes and spheres do. Accordingly, electrospun Ce–Mn oxide exhibits better catalytic activity than reference catalysts, including Ce–Mn oxides by co-precipitation and sol-gel methods. The characterizations suggest that Mn3+ substitution into fluorite-type CeO2 enhances the reducibility through the acceleration of Mn–Ce electron transfer, improves the lattice oxygen mobility by weakening the Ce–O bonds, and induces oxygen vacancies for the activation of O2. The theoretical calculation reveals that the release of lattice oxygen becomes easy because of a low formation energy of oxygen vacancy, while the high reduction potential is beneficial for the activation of O2 on Ce3+-Ov (oxygen vacancies). Due to above Ce–Mn synergy, the CeMnOx-ES shows more active oxygen species and higher oxygen storage capacity than CeO2-ES and MnOx-ES. The theoretical calculation and experimental results suggest that the adsorbed O2 is more active than lattice oxygen and the catalytic oxidation mainly follows the Langmuir-Hinshelwood mechanism. This study indicates that electrospinning is a novel method to obtain efficient Ce–Mn oxide.

Revealing active edge sites induced by oriented lattice bending of Co-CeO2 nanosheets for boosting auto-exhaust soot oxidation

Herein, a series of Cox-CeO2 nanosheet catalysts were elaborately synthesized by a one-step hydrothermal method. The CeO2 microsphere with crossed nanosheets can improve the soot-catalyst contact efficiency and the lattice substitution of Co ions for cerium sites in CeO2 results in the oriented lattice bending of Co-CeO2 nanosheets for improving adsorption/activation properties of NO and O2. Co2-CeO2 catalyst displays the highest H2O-tolerance activity (T50 = 334 °C, TOF = 1.32 h−1) and excellent stability during soot oxidation in the presence of H2O. Combined with characterizations and DFT calculations, the mechanism was proposed: the active edge sites located at the oriented lattice bending of Co-CeO2 nanosheets can activate surface oxygen and gaseous O2, and active oxygen species can boost NO oxidation to NO2, which is a crucial step of NOx-assistant catalytic mechanism for soot oxidation. It provides a promising way for the rational design of high-performance non-noble metal catalysts for soot oxidation in practical applications.

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.

Soot oxidation over Pt-loaded CeO2-ZrO2 catalysts under gasoline exhaust conditions: Soot-catalyst contact efficiency and Pt chemical state

Decreasing the ignition temperature of soot combustion is a key of the improved catalyst performances, but a much lower concentration of oxygen from gasoline vehicle exhaust makes the research of the catalyst extremely challenging. Improving the adsorption and activation of oxygen molecules on the catalyst surface and the effective migration rate of active oxygen species are the key factors to enhance soot oxidation. In this work, Pt/CeO2-ZrO2-re catalyst was synthesized by synergistically adjusting CeO2-ZrO2 pore structure and Pt chemical state, as a result, the conversion temperature (T50, 50% soot was oxidized) was reduced by 113 ℃ in 1% O2/N2. The pore structure of CeO2-ZrO2 was optimized by copolymerization microsphere template assisted method, and better soot-contact efficiency and intrinsic properties were obtained, resulting in a higher availability of reactive oxygen species. In addition, adjusting Pt chemical state by using the liquid phase reduction method is significant for the adsorption and activation of oxygen molecules and catalytic cycle of soot oxidation. Structure-activity relationship studies showed that soot oxidation performance is highly related to the initial oxidation state of Pt and pore structure in 1% O2/N2. Better soot-contact efficiency, improved intrinsic properties and the existence of metallic Pt are responsible for the higher soot oxidation activity of Pt/CeO2-ZrO2-re catalyst.

Metal–Support Interactions on Ag/Co3O4 Nanowire Monolithic Catalysts Promoting Catalytic Soot Combustion

Tuning metal–support interactions (MSIs) is an important strategy in heterogeneous catalysis to realize the desirable metal dispersion and redox ability of metal catalysts. Herein, we use pre-reduced Co3O4 nanowires (Co-NWs) in situ grown on monolithic Ni foam substrates to support Ag catalysts (Ag/Co-NW-R) for soot combustion. The macroporous structure of Ni foam with crossed Co3O4 nanowires remarkably increases the soot–catalyst contact efficiency. Our characterization results demonstrate that Ag species exist as Ag0 because of the equation Ag+ + Co2+ = Ag0 + Co3+, and the pre-reduction treatment enhances interactions between Ag and Co3O4. The number of active oxygen species on the Ag-loaded catalysts is approximately twice that on the supports, demonstrating the significant role of Ag sites in generating active oxygen species. Additionally, the strengthened MSI on Ag/Co-NW-R further improves this number by increasing metal dispersion and the intrinsic activity determined by the turnover frequency of these oxygen species for soot oxidation compared with the catalyst without pre-reduction of Co-NW (Ag/Co-NW). In addition to high activity, Ag/Co-NW-R exhibits high catalytic stability and water resistance. The strategy used in this work might be applicable in related catalytic systems.

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.

Preparation of Cerium-Bismuth Oxide Catalysts for Diesel Soot Oxidation Including Evaluation of an Automated Soot-Catalyst Contact Mode.

Cerium‐bismuth oxides have emerged as promising candidates for Diesel soot oxidation. The catalysts are synthesized via automated co‐precipitation methods. T50 values, where 50 % of soot is oxidized, and the dynamic oxygen storage capacity (OSCdyn) are used to compare the catalytic activity. The activity is measured by thermogravimetric methods. The synthesized catalysts are characterized through powder X‐ray diffraction (PXRD), Raman spectroscopy, and specific surface area (SBET) measurements. This work investigates the influence of the contact mode between soot and catalyst. The literature‐known manual contact modes “loose”, “tight”, and “wet” are compared with our developed automated contact mode, using a dual asymmetric centrifuge. The rotation speed rs and mixing time tM have been varied independently. Both factors influence the T50 value. A continuous transition from loose to tight contact mode with increasing rotation speed rs can be shown. Furthermore, the automated contact mode shows better reproducibility behavior compared to manual contact modes.

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.

Shaping a soot combustion Ce0.5Pr0.5Ox catalyst

A Ce0.5Pr0.5Ox soot combustion catalyst has been shaped combining this material prepared in two different structures (nanoparticles and MS-macroporous) in a single active phase. Nanoparticles, prepared by reversed microemulsion method, provide high activity to the hybrid material, and the MS structure, obtained by a hard template synthesis method, provides high thermal stability and improved soot-catalyst contact. Ce0.5Pr0.5Ox nanoparticles present high surface area (148 m2/g; 5 nm) and improved redox properties with regard to other Ce0.5Pr0.5Ox structures, and the macropores size of MS Ce0.5Pr0.5Ox are large enough (around 100 nm) to properly disperse Ce0.5Pr0.5Ox nanoparticles inside and also to host soot particles, creating a high reactive catalyst environment. As a result, the as prepared Ce0.5Pr0.5Ox hybrid catalyst, mixed in loose-contact mode with soot, decreased soot combustion by ca. 100 °C with regard to the uncatalyzed reaction, and thermal aging at 800 °C only decreased this difference to ca. 75 °C. The as-prepared counterpart hybrid catalyst obtained dispersing pure ceria nanoparticles on pure ceria MS support was also active for soot combustion, but the activity was almost lost completely upon thermal aging due to ceria sintering.

Optimizing Gasoline Soot Oxidation of Pt/Ceo2-Zro2 Catalysts Via Improving of Catalyst-Soot Contact Efficiency and Adjusting Pt Microchemical State

Optimizing Gasoline Soot Oxidation of Pt/Ceo2-Zro2 Catalysts Via Improving of Catalyst-Soot Contact Efficiency and Adjusting Pt Microchemical State

Biodiesel soot combustion: Analysis of the soot-catalyst contact in different experimental conditions

To simulate the oxidation of Biodiesel soot in a catalyzed Diesel Particulate Filter, oxidation experiments of undoped or Na-doped model soot were performed in the presence of Pt-Pd/Al2O3 under Temperature Programmed Oxidation and different carbon-catalyst configurations. Loose or tight contact was simulated by mixing soot and catalyst either with a spatula or in a mortar. Samples were characterized by Flame Atomic Adsorption Spectroscopy, Inductively Coupled Plasma-Optical Emission Spectroscopy, N2-physisorption, X-ray Photoelectron Spectroscopy, Raman Spectroscopy and Transmission Electron Microscopy coupled with Energy Dispersive X-Ray. The results showed that reducing the carbon granulometry led to an enhancement of the reactivity under NO2, due to the external combustion mechanism of carbon crystallite. In the absence of catalysts, no impact of the granulometry was observed under a flue gas containing NO and O2. A better catalyst efficiency was obtained when the carbon-catalyst contact was increased. In tight contact, a mechanism where NO2 can react adsorbed on a metallic site with a carbon site was proposed. In the presence of water, a simple addition of the catalytic activity of both water and Pt-Pd/Al2O3 catalyst impact on carbon oxidation was observed. The use of Biodiesel, simulated by Na-doped model soot, led to a significant increase in the catalyst efficiency in loose contact. Thus, a second mechanism was proposed, assuming that the doped sites play the role of NO2-reservoir and carrier between catalyst and carbon sites.

Nanostructured ceria-based catalysts doped with La and Nd: How acid-base sites and redox properties determine the oxidation mechanisms

In the present work, novel ceria-based nanocatalysts containing different quantities of La and Nd were prepared via hydrothermal synthesis. The effects of doping on the structural and physico-chemical properties of ceria were examined with several techniques, such as XRD, FESEM, TEM, Raman spectroscopy, XPS, H2-TPR and O2/NH3/CO2-TPD. The catalytic activity of doped ceria towards CO, NO and soot oxidation was evaluated in different conditions; in particular, the role of the catalyst-soot contact and the influence of NOx and water on the soot oxidation performances were investigated. La and Nd ions were well incorporated in ceria structure, but the final morphology was significantly altered. The introduction of trivalent cations was also associated with a higher abundance of defects and oxygen vacancies, but an excessive oxygen deficiency detrimentally affected the material reducibility and catalytic activity for CO and NO oxidation. Conversely, soot oxidation benefited from La and Nd addition. In particular, the Ce-La equimolar oxide exhibited outstanding performances in all the tested conditions, thanks to its optimal morphology and surface acidity. A detailed comparison with equimolar ceria-praseodymia allowed to investigate how acid-base sites and redox properties control the different catalytic mechanisms involved in standard and NOx-assisted soot oxidation.

Promoting effect of Rh-impregnation on Ag/CeO2 catalyst for soot oxidation

In this study, the effect of Rh on the catalytic properties of CeO2 was examined using a series of Rh-impregnated catalysts with different Rh loadings (Rh(x)Ce, x = 1, 2, 3, 5 wt%). The Rh species were highly dispersed over CeO2, and Rh(x)Ce exhibited higher soot oxidation activity than CeO2. In particular, the H2-TPR and O2-TPD profiles of the prepared catalysts indicated that Rh(2)Ce outperformed all other Rh(x)Ce catalysts owing to its high reducibility and desorption of active oxygen species at low temperatures. Moreover, an excessive Rh loadings resulted in an increase in the Rh3+/Rh0 and a decrease in the surface oxygen reducibility of the Rh(x)Ce catalysts. Subsequently, the promoting effect of Rh on the catalytic properties of Ag/CeO2 was evaluated using a Rh-impregnated Ag/CeO2 catalyst (Rh(2)Ag(5)Ce). The Rh species were well-dispersed over Ag/CeO2, and Rh(2)Ag(5)Ce presented a higher catalytic activity than the Ag/CeO2 catalyst. XPS analysis revealed that the interaction between Rh and Ag caused changes in the electronic states of Rh and Ag. Moreover, the soot-TPR and Raman spectra data revealed that the Rh(2)Ag(5)Ce catalyst could use active oxygen species at a lower temperature and generate a higher amount of reactive oxygen species than all other analyzed catalysts. Furthermore, macroporous Rh(2)Ag(5)Ce exhibited excellent activity, which was ascribed to the high soot-catalyst contact efficiency.

Boosting diesel soot catalytic combustion via enhancement of solid(catalyst)-solid(soot) contact by tailoring micrometer scaled sheet-type agglomerations of CeO2-ZrO2 catalyst

Solid(catalyst)-solid(soot) contact is a crucial factor in diesel soot catalytic combustion, and rationally optimizing solid(catalyst)-solid(soot) contact is a promising yet challenging pathway for improving catalytic diesel soot combustion performance. Here, we report a micrometer scaled sheet-type CeO2-ZrO2 soot oxidation catalyst. The nitrogen adsorption-desorption result indicates that soot particulates are barely able to enter into the inner pore of the catalyst (average pore size < 20 nm) due to the large size of filamentous soot agglomeration (reaching up to 1 μm). Thus the catalyst-soot contact mainly depends on the catalyst external surface and morphology. Electron microscope images confirm the presence of microsheet agglomerations of the prepared CeO2-ZrO2 catalyst, which is an advantage for enhancing the adherence of soot filaments on catalyst. Compared to common CeO2-ZrO2 particle catalyst, the CeO2-ZrO2 microsheet shows a remarkably higher macrolevel soot combustion performance. Interestingly, the single catalytic site activity (intrinsic activity) of CeO2-ZrO2 microsheet is not enhanced by the micro-structure. Thus the enhanced soot combustion efficiency could be ascribed to the improving of catalyst-soot contact. And therefore, this work suggests that constructing structured catalyst at micrometer level is an efficient way to improve the solid(catalyst)-solid(soot) contact efficiency and thereby boost the diesel soot combustion performance.

PrOx nanoparticles: Active and stable catalysts for soot combustion

PrOx nanoparticles (10 nm; 81 m2/g) were synthesized and analysed as soot combustion catalyst in comparation with other reference materials including CeO2 nanoparticles and PrOx and CeO2 catalysts with three dimensionally ordered (3DOM) and without controlled structure. PrOx nanoparticles reached the highest activity; T50 decreases from 603 °C (uncatalysed combustion) to 494 °C. This high activity can be attributed to the high surface area/low crystal size, which enhances the soot catalyst contact, and to the improved reducibility. PrOx nanoparticles kept high activity (T50 = 520 °C) after aging at 800 °C, being significantly more active than aged PrOx catalysts with 3DOM and uncontrolled structure and also significantly more active than all aged CeO2 catalysis which suffer almost total deactivation upon aging. In all cases, PrOx catalysts are more active than CeO2 counterpart materials with the same structure and thermal history, and this applies to nanoparticles, 3DOM and uncontrolled structures.

Highly reactive and thermally stable Ag/YSZ catalysts with macroporous fiber-like morphology for soot combustion

The contact between catalysts and soot has been widely held as a crucial factor affecting the catalytic soot combustion, while efforts to improve the catalyst-soot contact efficiency remain both highly desirable and challenging. Herein, a hierarchical Ag/YSZ catalyst with macroporous fiber-like morphology was synthesized via a template electrospinning method. Based on the quantitative approach developed in this work, the soot accessibility of this catalyst with engineered morphology was 6.75 times higher than that of a conventional bulk Ag/YSZ catalyst. After the ageing treatments at 800 °C, the silver species on the fibrous Ag/YSZ redispersed into fine Ag nanoparticles, which provided abundant electrophilic O− species and led to a T50 of 372 °C for soot combustion in a “loose” contact mode. This strategy of fabricating macroporous fiber-like materials provides a new opportunity to improve the soot elimination efficiency of catalyzed gasoline particulate filters.