Catalysts For Soot Oxidation Research Articles

Nature and role of Cu(II) species in doped C12A7 catalysts for soot oxidation

Two series of copper-doped mayenite catalysts (Cuₓ:C₁₂₋ₓA₇) were synthesized by one-pot-assisted solution combustion at different Cu loadings (0.06 ≤x ≤ 1) with the aim to correlate their performances in soot combustion and the nature and abundance of the different copper species present. The atmosphere composition influence, precisely of the presence of water, was also studied. It appears that Cu(II) interacted with the C12A7 matrix in three structurally different forms: isolated-Cu²⁺, clustered-Cu²⁺, and bulky CuO particles. Cu-C12A7 catalysts exhibited enhanced activity over bare-C12A7, both in terms of soot oxidation at low temperatures and CO₂ selectivity. The control over the dispersion of Cu, the texture, and superoxide concentration of the Cu-C12A7 catalysts achieved by adjusting the Cu loading and calcination temperature, appeared crucial in promoting the catalytic performance. We concluded that the well-dispersed clustered Cu²⁺ is the most likely active species responsible for the improved activity both under dry and wet conditions.

Fe-doped porous Co3O4 nanosheets with highly efficient catalytic performance for soot oxidation

A series of CoxFe1-x-PNS materials were synthesized at room temperature through the one-pot MgO-mediated method and were then used as catalysts for soot oxidation. Of all the catalyst samples prepared, the porous Co0.8Fe0.2-PNS nanosheets exhibited the highest catalytic performance for soot oxidation under both loose and tight contact modes. The 2D nanosheets provided a larger external surface area for contact between the catalyst and soot, and the porous structure was beneficial to the adsorption and diffusion of reactant gas. It was found that Fe was successfully doped in the lattice of Co3O4, and the mechanism regarding how Fe doping enhances intrinsic activity was investigated by a series characterization and DFT calculations. The results indicated that Fe doping made it easier to form oxygen vacancies and adsorb gaseous O2, which effectively improved the catalytic activity of soot oxidation. Hence, it is believed that the synergy between the well-defined porous nanosheets morphology and the properties induced by the doping of Fe resulted in better catalytic activity. This study also provided insight into the design of 2D transition metal oxides nanosheets as catalysts for soot oxidation.

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.

Promoting the generation of active oxygen species on 3DOM K/LaMnO3 interface by introducing CeO2 to boost the NOx-assisted soot combustion

Herein, a series of K, Ce modified 3DOM LaMnO3 catalysts, named K/xCe/LM (x = 0, 10, 15 and 20 wt%) had been prepared and used for NOx-assisted soot oxidation. 3DOM LaMnO3 employed as the matrix could offer an ideal environment to hinder the agglomeration of CeO2. Meanwhile, introducing CeO2 on the surface of LaMnO3 would drive the generation of Mn4+ and Ce3+ through the redox cycle of Ce4+ + Mn3+ ↔ Mn4+ + Ce3+, which was conclusive to the generation of oxygen vacancy. Further modification of xCe/LM catalysts with K could accelerate the redox cycle, generating more active oxygen species and enhance the NO2 utilization rate during the reaction. It was noted that high content of CeO2 would aggregate and plug the macropores, leading to a decrease in catalytic activity. Among all the catalysts, K/15Ce/LM samples with optimal Ce content demonstrated the best catalytic performance. The T50, TOF and Ea values were 377 ℃, 3.30 × 10-3 s−1 and 57 kJ·mol−1, respectively. Besides, K/15Ce/LM catalysts also possessed excellent reusability, structure stability and water-resistance. The implementation of this work might offer a significant insight into the fabrication of high-performance soot oxidation catalyst for practical application.

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.

Improving the Performance of BaMnO3 Perovskite as Soot Oxidation Catalyst Using Carbon Black during Sol-Gel Synthesis.

A series of BaMnO3 solids (BM-CX) were prepared by a modified sol-gel method in which a carbon black (VULCAN XC-72R), and different calcination temperatures (600–850 °C) were used. The fresh and used catalysts were characterized by ICP-OES, XRD, XPS, FESEM, TEM, O2-TPD and H2- TPR-. The characterization results indicate that the use of low calcination temperatures in the presence of carbon black allows decreasing the sintering effects and achieving some improvements regarding BM reference catalyst: (i) smaller average crystal and particles size, (ii) a slight increase in the BET surface area, (iii) a decrease in the macropores diameter range and, (iv) a lower temperature for the reduction of manganese. The hydrogen consumption confirms Mn(III) and Mn(IV) are presented in the samples, Mn(III) being the main oxidation state. The BM-CX catalysts series shows an improved catalytic performance regarding BM reference catalyst for oxidation processes (NO to NO2 and NO2-assisted soot oxidation), promoting higher stability and higher CO2 selectivity. BM-C700 shows the best catalytic performance, i.e., the highest thermal stability and a high initial soot oxidation rate, which decreases the accumulation of soot during the soot oxidation and, consequently, minimizes the catalyst deactivation.

Broccoli-like CeO2 with Hierarchical/Porous Structures, and promoted oxygen vacancy as an enhanced catalyst for catalytic diesel soot elimination

• Ce-MOFs is adopted for fabricating broccoli-like CeO 2 (BCL-CeO 2 ). • BCL-CeO 2 shows a higher activity than commercial CeO 2 (com-CeO 2 ). • BCL-CeO 2 fully converts soot to CO 2 while com-CeO 2 produced CO. • The tight contact modeenables BCL-CeO 2 to exhibit a low T ig of 295 °C. • The mechanism of NO-assisted soot oxidation is examined by DRIFTS. • BCL-CeO 2 is recyclable with high catalytic activity for soot oxidation. While CeO 2 is a promising catalyst for soot elimination, it is essential to develop CeO 2 with higher contact areas, and reactivity for effective soot oxidation as catalytic soot oxidation is dominantly controlled by structures, and surficial properties of catalysts. In this study, a Ce-Metal organic frameworks (MOFs) consisting of Ce and trimesic acid (TA) is employed as the precursor as CeTA exhibits a unique broccoli-like hierachitecture which is transformed into CeO 2 with a hierarchical structure consisting of nanofibers of CeO 2 bundled together, forming a broccoli-like CeO 2 nanostructure. More importantly, these CeO 2 nanofibers in this broccoli-like CeO 2 (BCL-CeO 2 ) possesses porous structures, and also more oxygen vacancies, enabling BCL-CeO 2 to become a promising catalyst for soot oxidation. Thus, BCL-CeO 2 shows a much higher catalytic activity than commercial CeO 2 nanoparticle (com-CeO 2 ) for soot oxidation with a significantly lower ignition temperature (T ig ). More importantly, while soot oxidation by com-CeO 2 leads to production of CO together with CO 2 , BCL-CeO 2 can completely convert soot to CO 2 . The tight contact mode also enables BCL-CeO 2 to exhibit a very low T ig of 295 °C, whereas the existence of NO and H 2 O also enhances the soot oxidation by BCL-CeO 2 to reduce the T ig . The mechanism of NO-assisted soot oxidation is also examined, and validated by DRIFTS to identify the presence and transformation of nitrogen-containing intermediates. BCL-CeO 2 is also recyclable over many consecutive cycles and maintained its high catalytic activity for soot oxidation. These results demonstrate that BCL-CeO 2 is a promising and easily-prepared hierarchitectured Ce-based catalyst for soot oxidation.

Experimental Study on Ag Modified Ceo2 as Catalyst for Soot Oxidation

Experimental Study on Ag Modified Ceo2 as Catalyst for 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.

Enhanced Catalytic Soot Oxidation by Ce-Based MOF-Derived Ceria Nano-Bar with Promoted Oxygen Vacancy

As CeO2 is a useful catalyst for soot elimination, it is important to develop CeO2 with higher contact areas, and reactivities for efficient soot oxidation and catalytic soot oxidation are basically controlled by structures and surface properties of catalysts. Herein, a Ce-Metal organic framework (MOFs) consisting of Ce and benzene-1,3,5-tricarboxylic acid (H3BTC) is employed as the precursor as CeBTC exhibits a unique bar-like high-aspect-ratio morphology, which is then transformed into CeO2 with a nanoscale bar-like configuration. More importantly, this CeO2 nanobar (CeONB) possesses porou, and even hollow structures, as well as more oxygen vacancies, enabling CeONB to become a promising catalyst for soot oxidation. Thus, CeONB shows a much higher catalytic activity than commercial CeO2 nanoparticle (comCeO) for soot oxidation with a significantly lower ignition temperature (Tig). Moreover, while soot oxidation by comCeO leads to production of CO together with CO2, CeONB can completely convert soot to CO2. The tight contact mode also enables CeONB to exhibit a very low Tig of 310 °C, whereas the existence of NO also enhances the soot oxidation by CeONB to reduce the Tig. The mechanism of NO-assisted soot oxidation is also examined, and validated by DRIFTS to identify the formation and transformation of nitrogen-containing intermediates. CeONB is also recyclable over many consecutive cycles and maintained its high catalytic activity for soot oxidation. These results demonstrate that CeONB is a promising and easily prepared high-aspect-ratio Ce-based catalyst for soot oxidation.

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.

Catalytic Materials for Gasoline Particulate Filters Soot Oxidation

The energy efficiency of Gasoline Direct Injection (GDI) engines is leading to a continuous increase in GDI engine vehicle population. Consequently, their particulate matter (soot) emissions are also becoming a matter of concern. As required for diesel engines, to meet the limits set by regulations, catalyzed particulate filters are considered as an effective solution through which soot could be trapped and burnt out. However, in contrast to diesel application, the regeneration of gasoline particulate filters (GPF) is critical, as it occurs with almost an absence of NOx and under oxygen deficiency. Therefore, in the recent years it was of scientific interest to develop efficient soot oxidation catalysts that fit such particular gasoline operating conditions. Among them ceria- and perovskite-based formulations are emerging as the most promising materials. This overview summarizes the very recent academic contributions focusing on soot oxidation materials for GDI, in order to point out the most promising directions in this research area.

Promotion Effects of Barium and Cobalt on Manganese Oxide Catalysts for Soot Oxidation

Promotion Effects of Barium and Cobalt on Manganese Oxide Catalysts for Soot Oxidation

Multifunctional Pt-Cu/TiO2 nanostructures and their performance in oxidation of soot, formaldehyde, and carbon monoxide reactions

The present research work discusses the influence of platinum nanoparticles on the catalytic activity of Cu/TiO2 catalysts for soot, formaldehyde, and carbon monoxide oxidation. The results showed that the size of the platinum nanoparticles, loaded on the Cu/TiO2 nanostructure, varied from 1 to 2 nm. The Pt-Cu/TiO2 catalyst exhibited effective catalytic performance in the oxidation of formaldehyde at 25 °C (99% of conversion), CO at 100 °C (90% of conversion) and soot at 300 °C (100% of conversion) due to the platinum particle size and Pt-Cu interaction, which developed Ti3+ and oxygen vacancies on TiO2. Moreover, the bimetallic catalyst consisted of a complex mixture of Cu2+, Cu1+, and Pt0 species. The Pt-Cu/TiO2 catalyst showed stability in the three different reactions from 20 to 300 °C.

Ordered macro-mesoporous nanostructure of Pd/ZrO2 catalyst for boosting catalytic NO-assisted soot oxidation

Herein, the hierarchical porous catalysts of three dimensional ordered macro-mesoporous (3DOMM) ZrO2-supported active Pd nanoparticles (NPs) were prepared by two-step methods of evaporation-induced self-assembly-colloid crystal template (EISA-CCT) and gas bubbling-assisted membrane reduction (GBMR). Ordered macroporous structure can enhance diffusion and mass transfer of soot particles; ordered mesoporous structure is beneficial to enhance activation ability for gaseous reactants. Synergistic effect of hierarchical porous structure in the catalysts is important to improve catalytic activity for soot oxidation. Pd/3DOMM-ZrO2 catalyst exhibits the highest activity (T50 = 404 °C) for soot oxidation compared with the single macroporous or mesoporous structure. The catalytic kinetics of hierarchical porous Pd/3DOMM-ZrO2 catalyst for soot oxidation was systemically investigated, i.e., its reaction rate is 0.038 μmol g-1 s−1 at 310 °C, which is 2.7-fold of power-type Pd/normal-ZrO2 catalyst (0.014 μmol g-1 s−1). The hierarchical porous structure is a good strategy to boost catalytic activity during soot oxidation.

Effects of La incorporation in catalytic activity of Ag/La-CeO2 catalysts for soot oxidation

Owing to strengthened regulations toward vehicle emissions, the use of diesel particulate filter technology to reduce particulate matter emissions has attracted significant attention. To achieve low temperature oxidation of particulate matter, numerous studies on Ag/CeO2 catalysts for soot oxidation have been reported. Herein, Ag/La-CeO2 catalysts with different La contents are synthesized and compared to analyze the effect of La. Hydrogen temperature programmed reduction analysis confirms that the reducibility increases with an increase in the La content in La-CeO2. X-ray photoelectron spectroscopy and Raman analysis confirm an increase of oxygen vacancies with La doping. Accordingly, the soot oxidation performances estimated by temperature programmed oxidation experiments increase with La doping. However, the catalytic activity of Ag/La-CeO2 exhibits a volcano trend. When an appropriate amount of La is incorporated in Ag/CeO2, peroxide generation and reducibility improve, thereby enhancing the soot oxidation performance. Conversely, the catalytic activities gradually decrease with excess La-doping. Scanning transmission electron microscopy analysis and density functional theory calculations confirm that excess amounts of La induce the sintering of Ag particles, which lead to the degradation of peroxide generation and reducibility of the catalysts. Consequently, an optimal amount of La incorporation on Ag/La-CeO2 results in the best soot oxidation performance.

Nickel and cobalt transfigured natural clay: a green catalyst for low-temperature catalytic soot oxidation

Modified 'natural clay' with Ni and Co nanoparticles explored as efficient catalyst for low-temperature soot oxidation activity studies.

Cesium as a dual function promoter in Co/Ce-Sn catalyst for soot oxidation

In this study, a 10 %Cs/3 %Co/Ce0.5Sn0.5O2 catalyst with outstanding soot oxidation performance was developed, by doping Cs to 3 %Co/Ce0.5Sn0.5O2. Remarkably, doping Cs lowered the T50 of the catalyst by 163 °C under a H2O/O2/N2 atmosphere and loose contact. It was also noteworthy that the 10 %Cs/3 %Co/Ce0.5Sn0.5O2 catalyst exhibited excellent water and sulfur dioxide resistances. Characterizations indicated that the doping of Cs had dual functional effects on soot catalytic oxidation. On one hand, the introduction of Cs induced the formation of more oxygen defects, which was beneficial to the activation of surface chemisorbed oxygen. On the other hand, it also benefited the catalytic performance by increasing the mobility of the surface-active oxygen species, which favored the contact between soot and catalyst. Therefore, the alkali metal cesium was found to be an excellent promoter for soot catalytic oxidation, and the developed 10 %Cs/3 %Co/Ce0.5Sn0.5O2 catalyst is very promising for practical applications in diesel soot oxidation.

Synergistic Effects of Multicomponents Produce Outstanding Soot Oxidation Activity in a Cs/Co/MnOx Catalyst.

The control of soot emission from diesel vehicles is of extraordinary importance to the environment, and catalytic removal of soot is a highly effective and clean method. Here, we report a novel, non-noble metal catalyst for application in the catalytic combustion of soot with superb activity and resistance to H2O and SO2. MnOx oxide was prepared via a hydrothermal method, and then, Cs and Co were loaded on MnOx by impregnation. The 5%Cs/1%Co/MnOx catalyst displayed excellent catalytic activity with values of T10 (332 °C), T50 (371 °C), and T90 (415 °C) under loose contact. The as-prepared catalysts were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), H2 temperature-programmed reduction (TPR), O2 temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption fine structure (XAFS). The results suggest that, after the introduction of Cs and Co into the MnOx oxide, more NO2 molecules take part in soot oxidation, exhibiting higher NO2 utilization efficiency; this is due to the synergistic effects of multiple components (Cs, Co, and Mn) promoting the generation of more surface-active oxygen and then accelerating the reaction between NO2 and soot. This study provides significant insights into the development of high-efficiency catalysts for soot oxidation, and the developed 5%Cs/1%Co/MnOx catalyst is a promising candidate for application in diesel particulate filters.

Facile synthesis of birnessite-type K2Mn4O8 and cryptomelane-type K2-xMn8O16 catalysts and their excellent catalytic performance for soot combustion with high resistance to H2O and SO2

Soot particles emitted from the diesel exhausts have caused serious air pollution and catalytic soot combustion is promising for soot abatement. In this work, two kinds of soot oxidation catalysts, including phase-pure birnessite-type K2Mn4O8 (K-OL-1) and cryptomelane-type K2-xMn8O16 (K-OMS-2), were successfully prepared by a very simple method. In preparation of these catalysts, KMnO4 and glucose were used in various proportions and different calcination temperatures employed. The as-prepared catalysts exhibit excellent catalytic performance in the loose contact mode with the presence of water (10 %). Specifically, most of them completely remove soot particles below 450 °C. More importantly, the birnessite-type K2Mn4O8 catalysts exhibit good tolerance for sulfur and water and the presence of water in the interlayer space is the reason for this property. The possible reaction mechanisms for soot combustion on K2Mn4O8 catalysts are related to reaction of active oxygen species and NO2-assisted oxidation. This work shed a light on the important role of the interlayer gallery species (K+, H2O) in the catalytic activity of the birnessite materials in soot combustion, which so far has not been recognized. Meanwhile, the birnessite-type K2Mn4O8 catalysts are low-cost, the excellent catalytic performance and simple synthesis method give them a great potential for industrial applications.