Activity For Soot Combustion Research Articles

Study on the coating of nano-particle and 3DOM LaCoO3 perovskite-type complex oxide on cordierite monolith and the catalytic performances for soot oxidation: The effect of washcoat materials of alumina, silica and titania

The novel catalysts of LaCoO3/ɤ-Al2O3/cordierite monolith, LaCoO3/SiO2/cordierite monolith, LaCoO3/TiO2/cordierite monolith were prepared by using aluminum oxide, silicon dioxide and titanium dioxide nanoparticles as washcoat and monolithic cordierite as the monolithic ceramic substrate.The obtained samples were characterized by means of XRD, SEM, EDS, BET, and ultrasonic vibration test (Medi II Pselecta). The surface area of the cordierite monolith-supported LaCoO3/ɤ-Al2O3 is larger than those of LaCoO3/SiO2 and LaCoO3/TiO2. The coating of alumina, silica oxide and titania nanoparticles could increase the surface area of monolithic cordierite and also endue the coated layer with engineered structure. The results of thermal treatment experiment indicate that the good thermal stability of the ɤ-Al2O3 coating on the cordierite. The ultrasonic vibration test results showed that the washcoat was adhered to the substrate strongly. The weight loss for the samples LaCoO3/ɤ-Al2O3/cordierite (the most desired preparation protocol in this study) eventually reached about 3%, which was considered as a low weight loss.The LaCoO3/ɤ-Al2O3/cordierite monolith catalysts were successfully prepared by coating ready-made 3DOM LaCoO3 (perovskite-type oxides) catalysts onmonolithic cordierite substrate with a dip-coating method by employing aluminasol for the first time. The catalytic activities of a series of monolithic catalystsLaCoO3/ɤ-Al2O3/cordierite, LaCoO3/ɤ-Al2O3/cordierite (3DOM-catalysts), LaCoO3/SiO2/cordierite, LaCoO3/TiO2/cordierite were evaluated for soot combustion. Thenano LaCoO3/ɤ-Al2O3/cordierite catalysts gave the highest catalytic activity for soot combustion among the studied catalysts. The T10, T50, T90 over the LaCoO3/ɤ-Al2O3/cordierite catalyst were 199.4°C, 340.5°C, 405.3°C, respectively, and sco2m was 99.9%.

Plausibility of potassium ion-exchanged ZSM-5 as soot combustion catalysts

Potassium (K) ion-exchanged ZSM-5 zeolites were investigated for catalytic soot combustion. X-ray absorption fine-structure (XAFS), Raman, in situ IR and NH3-temperature programmed desorption (NH3-TPD) confirmed the location of K+ at the ion-exchanged sites. Temperature-programmed oxidation (TPO) reactions showed that K-ZSM-5 decreased ignition tempeatures of soot combustion and increased selectivity to CO2. The improved activity for soot combustion by increasing K+-exchanged amounts via decreasing the Si/Al ratio reinforced the K+ ions participating in soot combustion. 18O2 isotopic isothermal reactions suggested the activation of gaseous oxygen by the K+ ions. This demonstrated a new appliction of alkali metal exchanged zeolites and the strategy for enhancement of catalytic soot combustion activity.

Pure and Fe-doped CeO2 nanoparticles obtained by microwave assisted combustion synthesis: Physico-chemical properties ruling their catalytic activity towards CO oxidation and soot combustion

A sample of pure CeO2 and two samples of Fe-doped CeO2 containing either 3 or 6 at.% Fe were obtained by microwave assisted combustion synthesis. The powders were extensively characterized by several techniques and tested as catalysts for both CO oxidation and soot combustion.As-synthesized CeO2 nanoparticles have a mostly squared shape and size well below 100nm; they are characterized by the presence of surface Ce3+ species likely due to the occurrence of very defective ceria crystalline phases, as revealed by HR-TEM. Oxidation at 400°C leads to the formation of a hydroxyls-rich surface, with several types of OH groups related to both Ce4+ and Ce3+ species; reduction in H2 at mild temperature (200°C) leads both to reduction of surface Ce4+ to Ce3+ and formation of new OH groups.With respect to CeO2 nanoparticles, Fe-doped ones have, as a whole, a larger size and less abundant surface OH species. A core-shell structure is inferred where Fe is mostly present in the shell, both in a secondary phase (CeFeO3) and as a dopant, finally lowering the band gap of the material. The presence of Fe improved samples reducibility, as shown by the lowering of the onset of temperature programmed reduction.Catalytic tests of CO oxidation showed that surface Fe species significantly improve the catalytic performance of the samples, by lowering the onset of CO conversion to CO2 especially at low Fe content (i.e. 3 at.%), whereas at 6 at.% Fe loading, the preferential formation of the secondary phase CeFeO3 occurs, finally lowering the CO conversion with respect to the sample containing 3 at.% Fe.Conversely, the soot combustion activity was higher for pure CeO2 nanoparticles, likely due to their smaller size, which increases the amount of solid–solid contact points between soot and the catalyst. However, a positive effect of the presence of surface Fe species on the catalytic activity towards soot combustion was observed, as well.

Catalytic Combustion of Soot Particulates over Rare Earth Pyrochlore Oxides Doped with Transition Metals

Catalytic combustion is an efficient way to remove soot particulates from automobile exhausts. A series of rare earth pyrochlore oxides La2Sn1.8TM0.2O7 (TM=Sn, Mn, Fe, Co, Cu) were prepared with CTAB-assisted sol-gel method. The products were characterized by XRD,N2 Adsorption-Desorption, SEM, FT-IR, H2-TPR and PL techniques. Their catalytic activity for soot oxidation was investigated by TPO under tight conditions in both O2 and NO+O2 atmospheres. After calcination at 900℃, the as-synthesized oxides with pure pyrochlore phase displayed nanospheres with diameter of 30-60 nm and relatively large surface areas. The partial substitution of Sn with transition metals largely influenced the reduction behavior of pyrochlores especially on the low temperature range in H2-TPR profiles, which was due to the interactions between Sn and transition metals. The improved oxygen mobility might be derived from the structure defects induced by transition metals doping, which could be helpful in oxidation reactions. In comparison with uncatalyzed reactions, the La2Sn2O7 catalyst exhibited modest catalytic activity for soot combustion, while transition metals incorporation further enhanced the activity and selectivity. The improved activity of transition metals doped samples was likely to be associated with the improved reducibility and increased surface oxygen vacancies on the pyrochlore oxides. The presence of NO in the gas phase significantly enhanced the soot oxidation activity, which was due to the promotion effect of NO2. Especially, the densities of active oxygen sites and turnover frequency (TOF) values of the catalysts, quantified by isothermal anaerobic titration with soot as a probe molecule, were used to explain the different soot combustion behaviors. Among the pyrochlore oxides, the Co-doped pyrochlore sample displayed the highest ignition activity and the largest intrinsic activity with TOF of 3.20×10-3 s-1.

Ordered micro/macro porous K-OMS-2/SiO2 nanocatalysts: Facile synthesis, low cost and high catalytic activity for diesel soot combustion

A series of novel oxide catalysts, which contain three-dimensionally ordered macroporous (3DOM) and microporous structure, were firstly designed and successfully synthesized by simple method. In the as-prepared catalysts, 3DOM SiO2 is used as support and microporous K-OMS-2 oxide nanoparticles are supported on the wall of SiO2. 3DOM K-OMS-2/SiO2 oxide catalysts were firstly used in soot particle oxidation reaction and they show very high catalytic activities. The high activities of K-OMS-2/SiO2 oxide catalysts can be assigned to three possible reasons: macroporous effect of 3DOM structure for improving contact between soot and catalyst, microporous effect of K-OMS-2 for adsorption of small gas molecules and interaction of K and Mn for activation of gas molecules. The catalytic activities of catalysts are comparable to or even higher than noble metal catalyst in the medium and high temperature range. For example, the T50 of K-OMS-2/SiO2-50, 328 °C, is much lower than those of Pt/Al2O3 and 3DOM Au/LaFeO3, 464 and 356 °C,respectively. Moreover, catalysts exhibited high catalytic stability. It is attributed to that the K+ ions are introduced into the microporous structure of OMS-2 and stabilized in the catalytic reaction. Meanwhile, the K+ ions play an important role in templating and stabilizing the tunneled framework of OMS-2.

The monolithic transition metal oxide crossed nanosheets used for diesel soot combustion under gravitational contact mode

Crossed nanosheets of transition metal oxide (TMO-NS: Co-NS, Mn-NS and Fe-NS) were synthesized by a facile hydrothermal method and employed for soot combustion in the NO/O2/N2 and O2/N2 atmosphere under gravitational contact mode (GCM). They show high catalytic activities for soot combustion due to the macroporous structure of the as-prepare catalysts increasing the soot-catalyst contact efficiency. The XRD and XPS results reveal that the active phases in the corresponding catalysts exist as Co3O4, Mn2O3 and Fe2O3, respectively. Among these catalysts, the Co-NS shows the best activity for soot combustion, especially in the presence of NO, whose catalytic activity of T50 (391°C) and SCO2 (100%) is as good as that of the Pt/Al2O3 catalyst. The excellent performance of the Co-NS catalyst results from several factors: the highest intrinsic activity (TOF=1.77×10−5s−1); the highest redox property as revealed by H2-TPR and soot-TPR; the largest amount of active oxygen species as clarified by XPS; the highest ability of NO oxidation to NO2 supported by NO-TPO. In addition, the multiporous structure of Co3O4 nanosheets is facilitated for the mass transfer. In the O2 atmosphere, soot particulates are directly oxidized by the surface adsorbed oxygen. After introducing of NO, the soot particulates are readily oxidized by NO2 at the low temperature (<330°C); with the increase of the reaction temperature (330–450°C), both the active oxygen species and NO2 involve in soot combustion.

Shape Effect of MnOx-Decorated CeO2 Catalyst in Diesel Soot Oxidation

Abstract A series of MnOx-decorated CeO2 (MnCeO) catalysts with different morphologies have been prepared by the shape-controlled synthesis of single-crystalline CeO2, such as nanorod, nanoparticle, and nanocube, by a hydrothermal method followed by the deposition of MnOx phase by a simple impregnation method. Their shape-dependent physicochemical properties were investigated by means of XRD, BET, UV–vis, HRTEM, XPS, TPR and oxygen storage/release properties measurements. The MnOx/CeO2 nanorod (MnCeO-NR) showed prominent carbon soot combustion activity at lower temperature under tight contact mode with a T50 temperature of 317 °C, which is attributed to larger surface area and higher oxygen release rate, as compared with particle and cubic catalysts. MnCeO-NR also exhibited higher catalytic activity (a shift of T50 by 127 °C) in NO-assisted soot combustion under a loose contact mode. Not only the higher surface area but also the superior NO conversion ability at low temperature as well as greater NO absorption contributes to the improved catalytic activities. The MnCeO-NR further displayed high stability and satisfactory recyclability without significant loss of catalytic activity. The use of cheaper combinations without noble metals makes the MnOx/CeO2 catalyst a promising candidate to satisfy future requirements in industry.

Highly active MnOx–CeO2catalyst for diesel soot combustion

Optimized Ce–Mn composite oxide, possessing abundant active Ce3+–Mn4+ions, exhibits excellent activity for catalytic soot combustion in NOx/O2.

Facile synthesis of spinel Cu1.5Mn1.5O4 microspheres with high activity for the catalytic combustion of diesel soot

Optimized Cu1.5Mn1.5O4 microspheres, possessing abundant Oads and active Cu+–Mn4+ sites for NO2 formation, exhibit excellent activity for soot combustion.

Cerium-copper oxides prepared by solution combustion synthesis for total oxidation reactions: From powder catalysts to structured reactors

A set of cerium-copper oxide catalysts with various Ce/Cu contents was synthesized using the solution combustion synthesis (SCS) technique. Catalytic activities of the prepared materials were tested for the CO oxidation, total oxidation of ethene and soot combustion. As a whole, the best performances in terms of both CO oxidation and ethene total oxidation were achieved for the binary oxide catalysts having Ce/Cu ratio ranging from 0.67 to 1.5. It has been observed that catalysts with CuOx clusters interacting with CeO2 are particularly effective for both the oxidation reactions. This confirms that CeOx and CuOx domains may cooperate synergistically, leading to higher oxidation activity because of the easier surface reducibility and more abundant structural defects (oxygen vacancies). On the other hand, the soot combustion activity increases as a function of the Ce-content up to 95 at.%. Indeed, the best soot oxidation catalyst exhibits copper highly dispersed into the ceria framework (Ce-O-Cu species), along with an abundant population of Cu+ species and H-bonded hydroxyl groups. Finally, the best performing powder catalysts were deposited on Silicon Carbide (SiC)-type monoliths through a novel synthesis and their catalytic activity was confirmed in a laboratory-scale pilot plant reactor. All the prepared catalysts were characterized by physico-chemical techniques, including XRD, FESEM, TEM, N2 physisorption at −196°C, H2-TPR, XPS, FT-IR and micro-Raman spectroscopies.

Strong Enhancement of deSoot Activity of Transition Metal Oxides by Alkali Doping: Additive Effects of Potassium and Nitric Oxide

A series of potassium-promoted spinels (Mn, Fe, Co) were prepared with various K+ promoter locations: on the surface (surface promotion) or in the bulk (formation of new layered and tunneled nanostructures via solid state reaction). All prepared samples were characterized by means of X-ray diffraction, Raman spectroscopy, X-ray fluorescence and N2-BET specific surface area analysis. Catalytic activity in soot combustion in different reaction conditions was investigated (tight contact, loose contact, loose contact with NO addition). It was shown that in all cases the nanostructuration is more effective than the surface promotion, with the layered structures of KCo4O8, KMn4O8 being the most catalytically active phases, lowering the soot combustion down to 250 °C. The difference in activity between tight and loose contacts can be bridged in the presence of NO due to its transformation into NO2, which acts as the oxygen carrier from the catalyst surface into soot particles, eliminating the soot-catalyst contact difference.

Role of chain length of the capping agents of iron oxide based fuel borne catalysts in the enhancement of soot combustion activity

A series of fuel borne catalysts (FBC) based on an iron oxide core stabilized by various long chain carboxylic acids were synthesized, characterized and tested in model soot combustion. As the capping agents methacrylic (C4), undecylenic (C11), oleic (C18) and erucic (C22) acids were used. The FBC precursors and the resultant catalysts were examined by Raman, FTIR, EPR, UV–vis and TEM/SAED techniques, whereas the catalytic reactivity in combustion of a model soot (Printex U) was evaluated by TG/DTA. For all the investigated FBC derived catalysts, it was found that the core of the catalyst consists of Fe2O3 of a crystallite size in range of 5–8nm, which is beneficial for the soot combustion activity. While a strong positive effect on the catalyst performance was observed for all the alkyl chain lengths, the best results were obtained for a hybrid FBC catalyst with two types (C11 and C18) of capping ligands. The effect of the chain length of the capping agent on the soot combustion process was discussed in terms of promotion of soot ignition by the more reactive C11 and combustion sustentation by heat transfer from the long chain C18 to soot particles, as implied by the observed overlapping of the combustion temperature windows of those moieties. For such hybrid catalysts, the ignition temperature of the soot combustion was lowered to almost 150°C, and the total soot combustion accomplished below ∼470°C. The high activity of the hybrid FBC catalysts makes them a promising alternative/backup for the particulate filter technology in light oil burners and related applications.

Effects of Au–Ce strong interactions on catalytic activity of Au/CeO2/3DOM Al2O3 catalyst for soot combustion under loose contact conditions

Au/3DOM (three-dimensionally ordered macroporous) Al2O3 and Au/CeO2/3DOM Al2O3 were prepared using a reduction-deposition method and characterized using scanning electron microscopy, N2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, ultraviolet-visible spectroscopy, temperature-programmed hydrogen reduction, and X-ray photoelectron spectroscopy. Au nanoparticles of similar sizes were well dispersed and supported on the inner walls of uniform macropores. The norminal Au loading is 2%. Al–Ce–O solid solution in CeO2/3DOM Al2O3 catalysts can be formed due to the incorporation of Al3+ ions into the ceria lattice, which causes the creation of extrinsic oxygen vacancies. The extrinsic oxygen vacancies improved the oxygen-transport properties. The strong metal–support interactions between Au and CeO2 increased the amount of active oxygen on the Au nanoparticle surfaces, and this promoted soot oxidation. The activities of the Au-based catalysts were higher than those of the supports (Al2O3 or CeO2/3DOM Al2O3) at low temperature. Au/CeO2/3DOM Al2O3 had the highest catalytic activity for soot combustion, with T10, T50, and T90 values of 273, 364, and 412 °C, respectively.

Simultaneous Removal of Soot and NOx Over Silver and Ruthenium-Based Catalysts

Silver- and ruthenium-based materials are herein investigated for the simultaneous removal of particulate matter (soot) and NOx and their behaviour is compared with that of a model Pt–Ba/Al2O3 catalyst. The catalytic activity for diesel soot combustion, in loose contact conditions, is studied by means of TPO (temperature programmed oxidation) while NOx removal is investigated through NOx Storage-Reduction cycles (SRC), performed both in the presence and in the absence of soot. Both the Ag- and Ru-based formulations result active in the soot oxidation, more than the traditional Pt-containing DPNR catalyst. Also, the Ru-based sample shows remarkable performances in the DeNOx-DeSoot activity, although its activity in the reduction step of the stored NOx still needs further improvements.

How to Efficiently Promote Transition Metal Oxides by Alkali Towards Catalytic Soot Oxidation

The effect of surface and bulk potassium promotion on the transition metal oxides (Mn, Fe, Co) catalytic activity in catalytic soot oxidation was investigated. The surface promotion was obtained via incipient wetness impregnation, whereas the bulk promotion—nanostructuration—was obtained via wet chemical synthesis or solid state reaction leading to mixed oxide materials. The introduction of potassium into the transition metal oxide matrix results in the formation of tunneled or layered structures, which enable high potassium mobility. The structure of the obtained materials was verified by powder X-ray diffraction and Raman spectroscopy and the catalytic activity in soot oxidation was determined by TPO-QMS and TGA. It was found that the surface promotion does not alter the metal oxide structure and leads to either enhancement (Mn, Fe) or deterioration (Co) of the catalytic activity. Simultaneously, the catalytic activity in soot combustion of the potassium structured oxides is strongly enhanced. The most active, cobalt oxide based catalyst significantly lowers the temperature of 50 % of soot conversion by ~350 °C comparing to the non-catalyzed process. The study allows for the establishment of rational guidelines for designing robust materials for DPF applications based on ternary metal oxides.

Effect of A-site deficiency in LaMn0.9Co0.1O3 perovskites on their catalytic performance for soot combustion

The influence of lanthanum stoichiometry in Ag-doped (La1-xAgxMn0.9Co0.1O3) and A-site deficient (La1-xMn0.9Co0.1O3-δ) perovskites with x equal to 10, 20 and 30 at.% has been investigated in catalysts for soot combustion. The catalysts were prepared by the amorphous citrate method and characterized by XRD, nitrogen adsorption, XPS, O2-TPD and TPR. The formation of a rhombohedral excess-oxygen perovskite for Ag-doped and a cubic perovskite structure for an A-site deficient series is confirmed. The efficient catalytic performance of the larger Ag-doped perovskite structure is attributed to the rhombohedral crystalline structure, Ag2O segregated phases and the redox pair Mn4+/Mn3+. A poor catalytic activity for soot combustion was observed with A-site deficient perovskites, despite the increase in the redox pair Mn4+/Mn3+, which is attributed to the cubic crystalline structure.

Bifunctional Catalyst of Core–Shell Nanoparticles Socketed on Oxygen-Deficient Layered Perovskite for Soot Combustion: In Situ Observation of Synergistic Dual Active Sites

In this letter, two functional reaction sites, i.e., massive Co core–shell nanoparticles and oxygen-deficient layered perovskite, have been combined into a bifunctional catalyst, which exhibits very high activity in soot combustion. Environmental transmission electron microscopy (TEM), in situ Raman spectroscopy, and other characterizations were applied simultaneously to study the soot consumption process online.

Simultaneous removal of soot and NOx over K- and Ba-doped ruthenium supported catalysts

Ruthenium-based materials are investigated for the simultaneous removal of soot and NOx and their behavior is compared with that of model Pt-Ba/Al2O3 and Pt-K/Al2O3 catalysts.The materials, 1%wt Ru–10%wt AM/MO (AM=Ba or K; MO=Ce0.8Zr0.2O2, ZrO2, Al2O3), have been prepared by incipient wetness impregnation and characterized by BET, XRD, HRTEM and TPR experiments. The catalytic activity for diesel soot combustion is studied under loose contact conditions by means of TPO (Temperature Programmed Oxidation) while the reactivity in the NOx removal is investigated by Isothermal Concentration Step Change experiments.All the ruthenium-based formulations are active in the combustion of diesel soot, particularly potassium-doped materials that show low onset temperatures, near 230°C. The catalytic activity in the simultaneous removal of soot and NOx shows that Ru-based catalysts are very efficient in the oxidation of soot also under isothermal conditions and that their NOx removal capacity (i.e. storage capacity) is almost comparable to that of traditional Pt-based LNT systems. However, the NOx reduction efficiency of the Ru-containing catalysts is lower than that of traditional LNT Pt-based catalysts.

Potential of Cu–saponite catalysts for soot combustion

A variety of H– and Na–saponite supports have been prepared by several synthesis approaches; the best activity for soot combustion was achieved with copper oxide supported on a Na–saponite prepared at pH 13 and with surfactant.

Boosting soot combustion efficiencies over CuO–CeO2 catalysts with a 3DOM structure

A CuO–CeO2 catalyst with a well-defined 3DOM structure exhibited superior catalytic activity for soot combustion compared to its 3DOM CeO2 counterpart.