Search Results (26)

The removal of soot particles via high-performance catalysts is a critical area of research due to the growing concern regarding air pollution. Among various potential catalysts suitable for soot oxidation, cerium oxide-based materials have shown considerable promise. In this study, CeO₂ samples obtained using a range of preparation methods (including hydrothermal synthesis (HT), sonochemical synthesis (SC), and hard template synthesis (TS)) were tested in soot combustion. They were compared to commercially available material (COM). All synthesized ceria catalysts were thoroughly characterized using XRD, RS, UV/Vis-DR, XPS, H₂-TPR, SEM, and TEM techniques. As confirmed in the current study, every tested ceria sample can be used as an effective soot oxidation catalyst, with a temperature of 50% soot conversion not exceeding 400 °C in a tight contact mode. A strong correlation was observed between the catalysts’ Ce³⁺ concentration and activity, with higher Ce³⁺ levels leading to improved performance. These findings underscore the importance of synthesis in optimizing ceria-based catalysts for environmental applications. Full article

The reaction mechanism of soot oxidation on Mn (Mn₃O₄), Mn-Ce (Mn₃O₄-CeO₂), and Ce (CeO₂) catalysts in tight contact conditions was investigated using ITKA (isotopic transient kinetic analysis). The obtained results suggest that lattice-bulk oxygen from all studied catalysts takes part in the soot oxidation process but with varying relative contributions: for the Ce catalyst, this contribution is practically 100%, whereas with decreasing Ce content in Mn-Ce catalysts, the significance of lattice-bulk oxygen for soot oxidation diminishes. For the Mn catalyst, it is estimated to be below 50%. Moreover, strong interactions between Mn and Ce ions were observed, increasing oxygen mobility in the catalyst crystal lattice and affecting the activity of Mn-Ce catalysts. Full article

Soot combustion experiments with 5%O₂/He were conducted using model soot, and four distinct compositions of Ce_xPr_1-xO_2-δ oxides of varying nominal cerium compositions (x = 0, 0.2, 0.3, and 1) were prepared. The catalyst samples were comprehensively characterized using techniques such as XRD, Raman spectroscopy, HR-TEM, N₂ adsorption at −196 °C, XPS, O₂-TPD, H₂-TPR, and work function measurements. The Pr-rich compositions, ranging from Ce_0.3Pr_0.7O_2-δ to PrO_2-δ, resulted in a significant increase in the total evolved O₂ amounts and enhanced catalyst reducibility. However, a decrease in the textural properties of the catalysts was noted, which was particularly important for the pure praseodymia under the synthesis route conducted. The catalytic activity was investigated under the two following contact modes of mixing between soot and catalyst: loose and tight. The results revealed that the catalytic performance is associated with the surface contact in tight contact mode and with the combination of surface/subsurface/bulk oxygen mobility and the BET surface area in loose contact mode. Notably, the temperatures estimated at 10% and 50% of the conversion (T₁₀ and T₅₀) parameters were achieved at much lower temperatures than the uncatalyzed soot combustion, even under loose contact conditions. Specifically, the 50% conversion was achieved at 511 °C and 538 °C for Ce_0.3Pr_0.7O₂ and Ce_0.2Pr_0.8O₂, respectively. While no direct correlation between catalytic activity and work function was observed, a significant relationship emerges between work function values and the formation of oxygen vacancies, whatever the conditions used for these measurements. On the other hand, the ability to generate a high population of oxygen vacancies at low temperatures, rather than the direct activation of gas-phase O₂, influences the catalytic performance of Pr-doped ceria catalysts, highlighting the importance of surface/subsurface oxygen vacancy generation, which was the parameter that showed a better correlation with the catalytic activity, whatever the soot conversion value or the mode of contact considered. Full article

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 La_2−xCe_xCoNiO₆ catalysts was investigated systematically. The optimized cerium doping ratio in La_2−xCe_xCoNiO₆ catalysts can improve the microenvironment for efficient soot-catalyst contact, enhancing the catalytic activity of soot oxidation. Among the catalysts, the 3DOM La_0.8Ce_1.2CoNiO₆ 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. Full article

A series of Co-M (M = Fe, Cr, and Mn) catalysts were synthesized by the sol-gel method for soot oxidation in a loose contact mode. The Co-Fe catalyst exhibited the best catalytic activity among the tested samples, with the characteristic temperatures (T₁₀, T₅₀, and T₉₀) of 470 °C, 557 °C, and 602 °C, respectively, which were 57 °C, 51 °C, and 51 °C lower than those of the CoO_x catalyst. Catalyst characterizations of N₂ adsorption–desorption, X-ray diffraction (XRD), X-ray photo-electron spectrometry (XPS), and the temperature programmed desorption of O₂ (O₂-TPD) were performed to gain insights into the relationships between the activity of catalytic soot oxidation and the catalyst properties. The content of Co²⁺ (68.6%) increased due to the interactions between Co and Fe, while the redox properties and the relative concentration of surface oxygen adsorption (51.7%) were all improved, which could significantly boost the activity of catalytic soot oxidation. The effects of NO and contact mode on soot oxidation were investigated over the Co-Fe catalyst. The addition of 1000 ppm of NO led to significant reductions in T₁₀, T₅₀, and T₉₀ by 92 °C, 106 °C, and 104 °C, respectively, compared to the case without the NO addition. In the tight contact mode, the soot oxidation was accelerated over the Co-Fe catalyst, resulting in 46 °C, 50 °C, and 50 °C reductions in T₁₀, T₅₀, and T₉₀ compared to the loose contact mode. The comparison between real soot and model Printex-U showed that the T₅₀ value of real soot (455 °C) was 102 °C lower than the model Printex-U soot. Full article

In this article, the catalysts of hydrotalcite-derived Ni_1.5Co_0.5AlO nanosheet-supported highly dispersed Pt nanoparticles (Pt_n/Ni_1.5Co_0.5AlO, where n% is the weigh percentage of the Pt element in the catalysts) were elaborately fabricated by the gas-bubble-assisted membrane--reduction method. The specific porous structure formed by the stack of hydrotalcite-derived Ni_1.5Co_0.5AlO nanosheets can increase the transfer mass efficiency of the reactants (O₂, NO, and soot) and the strong Pt–Ni_1.5Co_0.5AlO interaction can weaken the Ni/Co-O bond for promoting the mobility of lattice oxygen and the formation of surface-oxygen vacancies. The Pt_n/Ni_1.5Co_0.5AlO catalysts exhibited excellent catalytic activity and stability during diesel soot combustion under the loose contact mode between soot particles and catalysts. Among all the catalysts, the Pt₂/Ni_1.5Co_0.5AlO catalyst showed the highest catalytic activities for soot combustion (T₅₀ = 350 °C, TOF = 6.63 × 10⁻³ s⁻¹). Based on the characterization results, the catalytic mechanism for soot combustion is proposed: the synergistic effect of Pt and dual Ni/Co cations in the Pt/Ni_1.5Co_0.5AlO catalysts can promote the vital step of catalyzing NO oxidation to NO₂ in the NO-assisted soot oxidation mechanism. This insight into the synergistic effect of Pt and dual Ni/Co cations for soot combustion provides new strategies for reducing the amounts of noble metals in high-efficient catalysts. Full article

In this work, a series of CuCo₂O₄-x (x = N, A and C) catalysts were synthesized using different metal salt precursors by urea hydrothermal method for catalytic soot combustion. The effect of CuCo₂O₄-x catalysts on soot conversion and CO₂ selectivity in both loose and tight contact mode was investigated. The CuCo₂O₄-N catalyst exhibited outstanding catalytic activity with the characteristic temperatures (T₁₀, T₅₀ and T₉₀) of 451 °C, 520 °C and 558 °C, respectively, while the CO₂ selectivity reached 98.8% during the reaction. With the addition of NO, the soot combustion was further accelerated over all catalysts. Compared with the loose contact mode, the soot conversion was improved in the tight contact mode. The CuCo₂O₄-N catalysts showed better textural properties compared to the CuCo₂O₄-A and CuCo₂O₄-C, such as higher specific surface areas and pore volumes. The XRD results confirmed that the formation of a CuCo₂O₄ crystal phase in all catalysts. However, the CuO crystal phase only presented in CuCo₂O₄-N and CuCo₂O₄-A. The relative contents of Cu²⁺, Co³⁺ and O_ads on the surface of CuCo₂O₄-x (x = N, A and C) catalysts were analyzed by XPS. The CuCo₂O₄-N catalyst displayed the highest relative content of Cu²⁺, Co³⁺ and O_ads. The activity of catalytic soot combustion showed a good correlation with the order of the relative contents of Cu²⁺, Co³⁺ and O_ads. Additionally, the CuCo₂O₄-N catalyst exhibited lower reduction temperature compared to the CuCo₂O₄-A and CuCo₂O₄-C. The cycle tests clarified that the copper–cobalt spinel catalyst obtained good stability. In addition, based on the Mars–van Krevelen mechanism, the process of catalytic soot combustion was described combined with the electron transfer process and the role of oxygen species over CuCo₂O₄ spinel catalysts. Full article

Diesel soot particles are of concern for both the environment and health. To catalytically remove them, it is important to know their structure and composition. There is little described in the literature on how catalysts favor the combustion of different soot fractions. In this work, programmed temperature oxidation (TPO) experiments were carried out using Co,Ce or Co,Ba,K catalysts supported on ceramic papers. Soot particles were obtained by burning diesel fuel in a vessel (LabSoot) or by filtering exhaust gases from a turbo diesel engine in a DPF filter (BenchSoot), and compared with a commercial diesel soot: Printex U. Various characterization techniques were useful to relate the characteristics of both the soot particles and the catalysts with the TPO results. The maximum catalytic soot burn rate (T_M) temperatures were in the range of diesel exhaust temperatures that would facilitate in-situ regeneration of the DPF. The Co,Ba,K catalyst showed a higher catalytic effect in LabSoot, as the latter exhibited the largest primary particles and the higher order of graphene layers, for which the potassium-containing catalyst improves the contact between soot and catalyst and favors the combustion of soot, while the Co,Ce catalyst preferentially enhanced the combustion of commercial soot by supplying active oxygen. Full article

In this paper, cerium was incorporated into polyhydroxyltriacetictin (PHTES) using the sol-gel method combined with electrospinning technology to prepare a series of composite oxide fiber catalysts Sn_xCe_1−xO₂ in different proportions. The structures and soot catalytic activities of Sn_xCe_1−xO₂ fibers were studied under loose contact conditions. When Ce entered the crystal lattice of SnO₂, the structural symmetry of the SnO₂ was destroyed, which inhibited the crystallization and grain growth of the fiber, and fiber catalysts with a larger specific surface area were obtained. Moreover, the introduction of Ce improved the number of oxygen vacancies and redox ability of the catalyst, thus promoting the catalytic activity of the catalyst for soot particles. In particular, among them, the Sn_0.7Ce_0.3O₂ fiber catalysts had the strongest catalytic oxidation ability regarding soot particles and could oxidize soot particles at a lower temperature and faster catalytic rate. The results of the temperature-programmed oxidation of Sn_0.7Ce_0.3O₂ fiber catalyst, conducted three times under the same conditions, were basically consistent, indicating that the experimental results are reliable and repeatable. In addition, the Sn_0.7Ce_0.3O₂ fiber catalyst showed good cycle stability. Full article

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 (T_ig). 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 T_ig of 310 °C, whereas the existence of NO also enhances the soot oxidation by CeONB to reduce the T_ig. 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. Full article

A set of manganese oxide catalysts was synthesized via two preparation techniques: solution combustion synthesis (Mn₃O₄/Mn₂O₃-SCS and Mn₂O₃-SCS) and sol-gel synthesis (Mn₂O₃-SG550 and Mn₂O₃-SG650). The physicochemical properties of the catalysts were studied by means of N₂-physisorption at −196 °C, X-ray powder diffraction, H₂ temperature-programmed reduction (H₂-TPR), soot-TPR, X-ray photoelectron spectroscopy (XPS) and field-emission scanning electron microscopy (FESEM). The high catalytic performance of the catalysts was verified in the oxidation of Volatile Organic Compounds (VOC) probe molecules (ethene and propene) and carbon soot in a temperature-programmed oxidation setup. The best catalytic performances in soot abatement were observed for the Mn₂O₃-SG550 and the Mn₃O₄/Mn₂O₃-SCS catalysts. The catalytic activity in VOC total oxidation was effectively correlated to the enhanced low-temperature reducibility of the catalysts and the abundant surface O_α-species. Likewise, low-temperature oxidation of soot in tight contact occurred over the Mn₂O₃-SG550 catalyst and was attributed to high amounts of surface O_α-species and better surface reducibility. For the soot oxidation in loose contact, the improved catalytic performance of the Mn₃O₄/Mn₂O₃-SCS catalyst was attributed to the beneficial effects of both the morphological structure that—like a filter—enhanced the capture of soot particles and to a probable high amount of surface acid-sites, which is characteristic of Mn₃O₄ catalysts. Full article

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. Full article

A series of Nb-doped (0–23 wt%) cryptomelane catalyst (Nb-K-OMS-2) was synthesized and thoroughly characterized by XRD, TEM/EDX, XRF, XPS, XAS, UV-Vis, and Raman techniques corroborated by the work function measurements. The obtained catalysts were tested for soot oxidation (Printex U) in model tight and loose contact modes. It was shown that the catalytic properties of the Nb-K-OMS-2 are controlled by the amount of Nb dopant in a strongly non-monotonous way. The introduction of niobium gives rise to the strain in the cryptomelane lattice, accompanied by significant Mn⁺³/Mn⁺⁴ ratio variations and concomitant work function changes. The isotopic exchange experiments revealed that the catalytic activity of the Nb-OMS-2 catalysts in soot combustion proceeds via the pathways, where both the activated suprafacial ¹⁸O and the surface ¹⁶O²⁻ species participate together in the reaction. The niobium doping level controls the non-monotonous changes of the catalyst work function and the lattice strain, and variations of these parameters correlate well with the observed deSoot activity. To our best knowledge, the role of the lattice strain of the cryptomelane catalysts was documented for the first time in this study. Full article

Soot-catalyst contact represents the main critical issue for an effective regeneration of catalytic (i.e., catalyst-coated) diesel particulate filters (DPFs). Most of the literature reviews on this topic have mainly been focused on studies dealing with powdered soot-catalyst mixtures. Although the results obtained on powders surely provide significant indications, especially in terms of intrinsic activity of materials towards soot oxidation, they cannot be directly extended to DPFs due to completely different soot-catalyst contact conditions generated during filtration and subsequent regeneration. In this work, attention is devoted to catalytic DPFs and, more specifically, studies on both catalyst dispersion and soot distribution inside the filter are critically reviewed from the perspective of soot-catalyst contact optimization. The main conclusion drawn from the literature analysis is that, in order to fully exploit the potential of catalytic DPFs in soot abatement, both a widespread and homogeneous presence of catalyst in the macro-pores of the filter walls and a suitably low soot load are needed. Under optimal soot-catalyst contact conditions, the consequent decrease in the temperature required for soot oxidation to values within the temperature range of diesel exhausts suggests the passage to a continuous functioning mode for catalytic filters with simultaneous filtration and regeneration, thus overcoming the drawbacks of periodic regeneration performed in current applications. Full article

ZrO₂ and Ce_0.8Zr_0.2O₂ mixed oxides were prepared and tested in the oxidation of carbon soot at different oxygen partial pressures and degrees of catalyst/soot contact to investigate their activity under typical gasoline direct injection (GDI) operating conditions. Under reductive atmospheres, generation of oxygen vacancies occurs in Ce_0.8Zr_0.2O₂, while no reduction is observed on ZrO₂. Both materials can oxidize carbon under high oxygen partial pressures; however, at low oxygen partial pressures, the presence of carbon can contribute to the reduction of the catalyst and formation of oxygen vacancies, which can then be used for soot oxidation, increasing the overall performance. This mechanism is more efficient in Ce_0.8Zr_0.2O₂ than ZrO₂, and depends heavily on the interaction and the degree of contact between soot and catalyst. Thus, the ability to form oxygen vacancies at lower temperatures is particularly helpful to oxidize soot at low oxygen partial pressures, and with higher CO₂ selectivity under conditions typically found in GDI engine exhaust gases. Full article