Catalytic Combustion Of Soot Research Articles

Model Ag/CeO2 catalysts for soot combustion: Roles of silver species and catalyst stability

Ag/CeO2 has been regarded as a promising recipe for soot catalytic combustion in gasoline particulate filters, while lots of information about its reaction mechanism and practicability is yet missing. In this work, the reducibility and activity of three Ag/CeO2 model catalysts with different types of silver species (Agn+ nanoclusters, metallic Ag nanoclusters and metallic Ag nanoparticles) supporting on CeO2 nanorods were studied. It was suggested that silver facilitated the generation of Oxn- via Ag+-(Ce3+-VO)-induced O2 activation or ceria bulk-to-surface oxygen migration, both of which resulted in boosted soot combustion. From a practical point of view, the thermal ageing-induced silver sintering could be alleviated by the defective sites on CeO2, though certain degree of catalyst deactivation was still inevitable.

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.

Effect of surface manganese oxide species on soot catalytic combustion of Ce–Mn–O catalyst

Constructing cerium and manganese bimetallic catalysts with excellent catalytic performance for soot combustion is the research frontier at present. In order to find out the key factors for catalytic soot combustion of Ce–Mn–O catalysts, a series of Ce–Mn–O catalysts with different Ce/Mn proportions were prepared by co-precipitation method. The activity test results show that it increases first and then decreases with the increase of Mn content. The best catalytic activity is obtained for Ce0.64Mn0.36 catalyst, which shows a maximum rate temperature (Tm) at 306 °C for CO2 production in TPO curve. Compared with non-catalytic soot combustion, the Tm decreases by more than 270 °C. Systematical characterization results suggest that when the adsorbed surface oxygen, lattice oxygen, specific surface area and total reduction amount of the catalysts reach a certain value, the key factors leading to the difference of catalytic activity become the readily reducible and highly dispersed surface manganese oxide species and contact performance of the external surface. The surface manganese oxide species is beneficial to improving the low-temperature reducibility of catalysts and the porous surface is conducive to the contact between catalyst and soot. Furthermore, for the soot combustion reaction containing only O2, the promoting effect of Mn4+ is not obvious.

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.

Exposed {0 0 1} facet of anatase TiO2 nanocrystals in Ag/TiO2 catalysts for boosting catalytic soot combustion: The facet-dependent activity

Herein, the nanocatalysts of Ag nanoparticles (NPs) coated on anatase TiO2-n% nanocrystals with co-exposed {101} and {001} facets were elaborately constructed by the urea-induced hydrothermal method. The ratios (n%) of exposed {001} facet in TiO2 nanocrystals are adjusted in the range of 8–79%. Ag/TiO2-n% catalysts exhibited excellent the exposed {001} facet-dependent catalytic activity during soot combustion. Ag/TiO2-79% catalyst shows the highest catalytic activity (T50 = 364 °C, TOF = 0.174 h−1 at 310 °C) and the lowest apparent activation energy (84 kJ mol−1). Combination in-situ Raman spectra and density functional theory (DFT) calculations, the catalytic mechanism is proposed: the active sites locate at the interface between Ag and {001} facet of TiO2-n% nanocrystal, and the synergy effect of coordinatively unsaturated Ti5c and adjacent Ag atoms boosts the key step of O2 activation. It highlights an effective strategy to develop high-efficient catalysts by the crystal facet engineering of metal oxides during oxidation reaction.

Synergy of NTP-La1-xAgxMn1-yCoyO3-δ Hybrid for Soot Catalytic Combustion at Low Temperature

Ag and Co co-doped La1-xAgxMn1-yCoyO3-δ perovskites were prepared by the citric acid sol–gel method. The maximum solubility of Ag+ in LaMnO3 decreased with the increase of Co doped in B-site, which lead to the exsolution of excess Ag+ from A-site of perovskite. The exsolution progress is more favorable to the formation of uniform and stable Ag nanoparticles on the perovskite substrate. The non-thermal plasma (NTP) assisted La1-xAgxMn1-yCoyO3-δ for soot catalytic combustion had been investigated under diesel exhaust gas conditions. When La1-xAgxMn1-yCoyO3-δ was utilized as the catalyst without NTP, the soot could hardly be oxidized at 200 °C. However, when La1-xAgxMn1-yCoyO3-δ was combined with NTP, the efficiency of soot removal was dramatically improved. The NTP-La0.5Ag0.5Mn0.8Co0.2O3-δ hybrid had the highest soot removal efficiency and CO2 selectivity. The combination of NTP and La1-xAgxMn1-yCoyO3-δ could form a synergistic catalytic effect, which significantly promoted the combustion of soot at low temperature. The results of characterization and experiments indicated that the synergistic catalytic performance depended on the coordination of short-living species in plasma, adsorbed oxygen and Ag nanoparticles on surface of La1-xAgxMn1-yCoyO3-δ. Based on these results, the reaction mechanism of plasma-catalyst hybrid for soot catalytic combustion was proposed.

Investigations on a new C-GPFs with electric heating for enhancing the integrated regeneration performance under critical parameters

In order to improve the uneven flow of exhaust in traditional catalytic gasoline particulate filter system (C-GPFs) and improve the regeneration performances under low-temperature conditions, the new C-GPFs integrated regeneration model is established and explored. In this work, firstly, the NO catalytic rate and soot combustion rate are defined as the evaluation indicators of the new C-GPFs integrated regeneration performances. Secondly, based on the numerical simulation software, the regeneration performances of the new C-GPFs with and without electric heating are compared and analyzed, and the calculation model is verified based on the engine experiments. Then, the effects of four different structure parameters on the regeneration performances of the new C-GPFs are studied. Finally, through the orthogonal experiments, the influence weights of the four parameters on NO catalytic rate, soot combustion rate, and pressure drop are explored, and the new C-GPFs are optimized under simulation conditions. The results show that after optimization, the NO catalytic rate is enhanced by 2.1%, the soot combustion rate is enhanced by 11.9%, and the pressure drop is increased by 3%. This work provides an important reference value for improving the integrated regeneration performance of the C-GPFs in a gasoline engine.

A nanorod-like KTi8O16 catalyst for soot combustion

A nanorod-like KTi8O16 catalyst was successfully prepared by combustion method and applied for removing hazardous diesel soot. The cryptomelane structure of KTi8O16 is confirmed by X-ray powder diffraction (XRD). The straight and smooth crystalline nanorods with the diameter of 180 nm are identified by transmission electron microscopy (TEM) and (200) facet is observed to be preferentially exposed. K cations are not freely present in cryptomelane structure of KTi8O16 derived from X-ray absorption fine-structure (XAFS) results, possibly due to the confinement or interaction of K with Ti element. By temperature-programmed oxidation (TPO) experiments, its catalytic soot combustion performance was evaluated, with T 10 and T m of 435°C and 511°C, which are decreased by 19°C and 45°C respectively compared with pure anatase TiO2. K+ species are deduced to serve as the active sites in the catalytic soot oxidation reaction, which are confined in the channels of the nanorod-like KTi8O16.

Investigation into the Anticoking Performances of Sol–Gel-Derived SiO2 and SiO2–CeO2 Coatings during Thermal Pyrolysis of Light Naphtha

CeO2-based materials are widely applied in a three-way catalyst framework for catalytic combustion of diesel soot. For the application of CeO2 in coking inhibition during thermal cracking of hydroc...

Synthesis of superficially modified Ce1−x(Zr + Y)xO2−δ solid solutions and thermogravimetric analysis of their performance in the catalytic soot combustion

In this work, solid solutions of general formula Ce1−x(Zr + Y)xO2−δ were chemically synthesized through the so-called citrate-EDTA complexing method, wherein the doping cations Zr and Y were substituted in the ceria lattice with an equimolar amount of 0.05 ≤ x ≤ = 0.25. The ternary oxides were heat-treated, and those that showed the best textural properties were superficially impregnated with Fe2O3 particles by the thermal decomposition method using a metalorganic precursor. The X-ray diffraction results suggest that co-doping with Zr4+ and Y3+ promotes a slight distortion of the CeO2 cubic cell. Nevertheless, the fluorite cubic structure of the oxides remains stable after being exposed to heat treatments. Furthermore, using scanning electron microscopy and Raman techniques, the presence of deposited Fe2O3 and the formation of extrinsic vacancies in the materials could be corroborated. Finally, the oxides’ catalytic evaluation in the soot oxidation reaction was carried out using the thermogravimetry technique. The ternary oxide with cerium molar content equal to 0.9 and impregnated with Fe2O3 presented excellent catalytic behavior for soot oxidation. T10, T50, and T90 temperatures were 310, 383, and 416 °C, respectively.

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.

Optimized Pt-MnOx interface in Pt-MnOx/3DOM-Al2O3 catalysts for enhancing catalytic soot combustion

The catalysts of three-dimensionally ordered macroporous (3DOM) Al2O3-supported core-shell structured Pt@MnOx nanoparticles (3DOM-Pt@MnOx/Al2O3) were successfully prepared by the gas bubbling-assisted membrane reduction-precipitation (GBMR/P) method. Pt@MnOx core-shell nanoparticles (NPs) are highly dispersed on the inner surface of 3DOM-Al2O3 support. Pt@MnOx/3DOM-Al2O3 catalysts, which combine both advantages of high-efficiency soot-catalyst contact by 3DOM-Al2O3 structure and the abundant active sites by the optimized Pt-MnOx interface, exhibit high catalytic activities for soot combustion, and the catalytic activities are strongly dependent on the thickness of MnOx shell. Among the catalysts, 3DOM-Pt@MnOx/Al2O3-1 catalyst with optimized Pt-MnOx interface shows the highest catalytic activity for soot combustion, i.e., its values of T50 and SCO2m are 351 °C and 98.6%, respectively. The highest density of Pt-MnOx active sites for adsorption-activation of gaseous O2 is responsible for enhancing catalytic activity for soot combustion. Pt@MnOx/3DOM-Al2O3 catalysts are promising to practical applications for the emission reduction of soot particles.

Electrospinning SnO2 fibers with 3D interconnected structure for efficient soot catalytic combustion

In this paper, SnO2 fibers with three-dimensional (3D) interconnected structure were successfully obtained by a simple electrospinning technique with both high quality and reproducibility. The microstructure, physicochemical properties were characterized (FT-IR, XRD, SEM, HR-TEM, TG-DSC, N2-BET, XPS, H2-TPR, O2-TPD) extensively. The catalytic activity was tested in temperature-programmed oxidation (TPO) of model soot. The influence of the heat-treated temperature on the catalysts physicochemical properties and reactivity was evaluated. The fibers were fluffy and self-supporting after heat-treated which could provide a beneficial environment favored by soot catalytic combustion. SnO2 fibers exhibited good thermal stability in phase structures and morphologies at least 900 °C. The SnF-500 exhibited the highest catalytic activity with T10, T50 and T90 at 410 °C, 450 °C and 474 °C. With the increase in the sintering temperature, the crystallinity of SnO2 fiber increases and the Sn–O-Sn bond strengthens, resulting in a decrease in the catalytic activity of the catalyst as the BET surface area and surface oxygen decrease. Our studies provide insights into SnO2 fibers for soot catalytic.

Investigations on the soot combustion performance enhancement of a catalytic gasoline particulate filter in equilibrium state for reducing the BSFC of gasoline direct injection engine

In catalytic gasoline particulate filter (CGPF), the higher soot oxidation rate and lower pressure drop symbolize the good soot combustion performance. In this work, the index for evaluating the catalytic efficiency is defined. Then, the effects of filter structural parameter on the catalytic efficiency and soot combustion performance of CGPF when it reaches equilibrium state are investigated through numerical simulation. The change rules of gasoline engine power and brake specific fuel consumption (BSFC) are analyzed by using the GT-power software. The results indicate that properly increasing the filter porosity, filter length, and filter diameter, or decreasing the filter wall thickness is beneficial for the improvement of soot combustion performance. For practical application, CGPF will obtain the best soot combustion performance when the filter porosity is 0.46, the filter wall thickness is 0.2 mm, the filter length is 200 mm, and the filter diameter is 158 mm. Comparing the optimized structural size with the initial structural size, the catalytic efficiency increases by 5.3%, the soot oxidation rate increases by 24.1%, and the pressure drop decreases by 37.5%. Based on GT-power modeling and analysis, the optimized CGPF reduces the BSFC by 2.6% and increases the power by 8.9%.

Potassium promoted macro-mesoporous Co3O4-La0.88Sr0.12CoO3−δ nanotubes with large surface area: A high-performance catalyst for soot removal

The construction of porous perovskite nanotubular materials with a good intrinsic activity, as well as a greater dispersion of the active sites is an effective strategy to obtain a high-performance catalyst used in soot removal. Thence, macro-mesoporous Co3O4-La0.88Sr0.12CoO3−δ nanotubes with large specific surface area (154.4 m2·g−1) from the acid etching of the porous La0.6Sr0.4CoO3−δ nanotubes, are supported by 5% K through bubbling method following calcination for soot combustion. The relationship between the specific surface area and K dispersion and their effect on the activity are studied by a series of isothermal kinetic measurements combined with the characterizations and activity evaluation results. It can be found that the greater the amount is of K+ incorporated into perovskite lattice, the better the dispersion of K, as well as the La2O2CO3 formed on the catalyst surface, thus leading to the enhanced performance in the soot catalytic combustion. As a result, the 5% K supported macro-mesoporous Co3O4-La0.88Sr0.12CoO3−δ nanotubes after acid etching show good activity and stability, where the T50 is 338 °C (5% O2 + 500 ppm NO + 6% H2O) with a good CO2 selectivity (above 99%), the activate energy is 78.1 kJ·mol−1, and the turnover frequency is 5.14 × 10−4 s−1.

Research progress of the preparation of perovskite oxide catalysts and their catalytic performances for soot combustion

Soot particles derived from the exhaust of diesel engines is one of the main sources of urban haze, which seriously pollute the environment and endanger people’s health. It is one of the most effective ways to eliminate soot particles by catalytic purification technology. In this way, the design and development of the catalysts with excellent performances is the most critical factor to determine whether this technology can be widely applied. Recently, perovskite oxide catalysts have been become a research hotspot in the catalytic combustion of soot particles due to the advantages of high activity, low costs and high stability. This review focuses on summarizing the preparation methods of perovskite oxide catalysts commonly used in recent years, such as sol-gel method, template method, coprecipitation method, hydrothermal synthesis method, and solid-state synthesis method. Meanwhile, perovskite catalysts with high activities for the soot catalytic combustion, such as Co-based perovskite, Mn-based perovskite, Fe-based perovskite, Ti-based perovskite, are also elaborated in detail. Moreover, the future research and development directions of perovskite oxide catalysts for the diesel soot catalytic combustion are prospected.

Most Recent Advances in Diesel Engine Catalytic Soot Abatement: Structured Catalysts and Alternative Approaches

Diesel engine emissions are typically composed of several hundred chemical compounds, partly present in the gas phase and partly in solid phase as particles, the so-called particulate matter or soot. The morphology of the catalyst is an important characteristic of soot particles’ abatement, since a good contact between catalyst and soot is mandatory. For practical purposes, the active species should be supported as a film on the structured carrier, in order to allow simultaneous soot filtration and combustion. This review focuses on the most recent advances in the development of structured catalysts for diesel engine catalytic soot combustion, characterized by different active species and supports, as well as by different geometric configurations (monoliths, foams, ceramic papers, or wire mesh); the most important peculiar properties are highlighted and summarized. Moreover, a critical review of the most recent advances in modeling studies is also presented in this paper. In addition, some highlights on some of the most recent alternative approaches proposed for limiting the soot emissions from diesel engines have been given, delineating feasible alternatives to the classical strategies nowadays used.

Diesel Soot Combustion over Mn2O3 Catalysts with Different Morphologies: Elucidating the Role of Active Oxygen Species in Soot Combustion

Catalytic diesel soot combustion was examined using a series of Mn2 O3 catalysts with different morphologies, including plate, prism, hollow spheres and powders. The plate-shaped Mn2 O3 (Mn2 O3 -plate) exhibited superior carbon soot combustion activity compared to the prism-shaped, hollow-structured and powdery Mn2 O3 under both tight and loose contact modes at soot combustion temperatures (T50 ) of 327 °C and 457 °C, respectively. Comprehensive characterization studies using scanning electron microscopy, scanning transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction and oxygen release measurements, revealed that the improved activity of Mn2 O3 -plate was mainly attributed to the high oxygen release rate of surface-adsorbed active oxygen species, which originated from oxygen vacancy sites introduced during the catalyst preparation, rather than specific surface-exposed planes. The study provides new insights for the design and synthesis of efficient oxidation catalysts for carbon soot combustion as well as for other oxidation reactions of harmful hydrocarbon compounds.

Synthesis and catalytic performance of macroporous La1-xCexCoO3 perovskite oxide catalysts with high oxygen mobility for catalytic combustion of soot

The disordered macroporous-mesoporous La1–xCexCoO3 catalysts were prepared by complex-combustion method with ethylene glycol as complexing agent at relatively low calcination temperature. The samples were characterized by means of X-ray diffraction, N2 adsorption-ndash;desorption, X-ray photoelectron spectroscopy, transmission electron microscopy, hydrogen temperature-programmed reduction and soot temperature-programmed reduction, and so on. The results show that the use of complexing agent and relatively low calcination temperature increase the specific surface area of the catalyst and have abundant pore structure. The Ce ions introduced into lattice of LaCoO3 mainly exist in the form of tetravalent. At the same time, Ce ions enhance the redox performance of the catalyst and the mobility of active oxygen species, which enhances the catalytic activity of the catalyst for soot combustion. The results of activity test show that La0.9Ce0.1CoO3 catalyst exhibits the highest activity in the absence of NO and NO2, and its T10, T50 and T90 are 371, 444, and 497 °C, respectively. At the same time, a possible reaction mechanism is proposed in this study based on the turnover frequency (TOF) calculated by isothermal anaerobic titrations, XPS and XRD results.