Catalytic Activity For Soot Combustion Research Articles

Magnesium borate whiskers/La2-XCeXZr2O7 catalysts preparation on cordierite honeycomb ceramic surfaces for soot catalytic oxidation͏

Magnesium borate whiskers were used to prepare a hierarchical microstructure on cordierite ceramic substrate through the precipitation-molten salt method. The La2-XCeXZr2O7 catalyst was then loaded onto the magnesium borate whiskers to form the hierarchical microstructure. The Ce-doped catalysts exhibited a significant improvement in the catalytic activity of soot combustion compared to the La2Zr2O7 catalyst. The study employed various techniques to characterize the structural morphology and phase composition, including scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform-infrared spectroscopy (FT-IR), and X-ray diffraction (XRD). The growth of Magnesium borate whiskers (Mg2B2O5) with diameters of 100-200 nm and lengths of 2-5 μm were grown and tightly bonded to the cordierite ceramic substrate to mimic the structure of human respiratory system cilia. This could improve the filtration efficiency of soot in car exhaust. BET analysis showed that the specific surface area of cordierite increased from 0.684 m2/g to 1.363 m2/g after whisker growth. The study confirmed that the whiskers were firmly attached to the cordierite ceramic substrate, as demonstrated by the binding strength experiments. The addition of Ce metal has been found to significantly enhance soot combustion due to the presence of more active oxygen species and superior mobility of lattice oxygen species with more oxygen vacancies. The catalyst's intrinsic redox property was characterized using X-ray photoelectron spectroscopy (XPS) and H2 temperature-programmed reduction (H2-TPR). The semi-quantitative thermogravimetric analysis (TG-DTG) and the temperature-programmed oxidation (TPO) of catalysts showed that Z-La1.9Ce0.1Zr2O7 exhibited the highest catalytic activity for soot combustion, with an ignition temperature of 268 °C, a peak temperature of 418 °C, and a temperature of 90% soot conversion of 464 °C. Furthermore, cyclic stability experiments demonstrate that the Z-La1.9Ce0.1Zr2O7 catalyst exhibits excellent structural stability and consistent catalytic performance. This distinctive microstructure holds great potential for applications in the field of DPF.

Synergistic Effect of Pt and Dual Ni/Co Cations in Hydrotalcite-Derived Pt/Ni1.5Co0.5AlO Catalysts for Promoting Soot Combustion

In this article, the catalysts of hydrotalcite-derived Ni1.5Co0.5AlO nanosheet-supported highly dispersed Pt nanoparticles (Ptn/Ni1.5Co0.5AlO, 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 Ni1.5Co0.5AlO nanosheets can increase the transfer mass efficiency of the reactants (O2, NO, and soot) and the strong Pt-Ni1.5Co0.5AlO interaction can weaken the Ni/Co-O bond for promoting the mobility of lattice oxygen and the formation of surface-oxygen vacancies. The Ptn/Ni1.5Co0.5AlO 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/Ni1.5Co0.5AlO 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/Ni1.5Co0.5AlO 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.

The promoting effect of Pt loaded with different redox supports on NO[sbnd]NO2 cycle-assisted soot combustion

Supports with different redox properties (Al2O3, Ce0.5Zr0.5O2-Al2O3, Ce0.5Zr0.5O2) and their corresponding Pt-based catalysts were prepared to investigate the effect of the suitability between Pt and different supports and the promotion of the NONO2 cycle on the catalytic activity of soot combustion. It is interesting that Pt-loaded nonredox support Al2O3 exhibited a poor catalytic activity for soot combustion in the absence of NO but an excellent catalytic activity in the presence of NO. However, unlike the Al2O3 support, Pt loaded Ce0.5Zr0.5O2-Al2O3 and Ce0.5Zr0.5O2 as redox supports showed an opposite result. N2 adsorption-desorption and XRD results indicated that Pt loading had no obvious effect on the texture properties of the supports. More zero-valent Pt (Pt0) on Pt/Al2O3 revealed by XRD, CO chemisorption and XPS was suggested as a major factor for promoting NO oxidizing cycles. Therefore, an amount of NO2 molecules produced on Pt0 is key to accelerate soot combustion under loose contact. The weak interaction between Pt and Al2O3 kept more Pt in the lower valence state. The Pt from Pt/Ce0.5Zr0.5O2-Al2O3 and Pt/Ce0.5Zr0.5O2 reduced the number of NONO2 cycles and further limited the assistance of NO2 in soot combustion due to a high-valence state of most of Pt. However, the preferable reducibility of the redox supports benefit soot combustion in O2/N2 because of the presence of active oxygen. This work would provide a new understanding for the further improvement of soot oxidation with the catalysts.

Highly Efficient Catalysts of AuPd Alloy Nanoparticles Supported on 3D Ordered Macroporous Al2O3 for Soot Combustion

AbstractThe catalysts of Au−Pd bimetallic nanoparticles with different Au/Pd ratios supported on 3DOM Al2O3 were synthesized by micropores‐diffused reduction (MDR) method. Compared with supported monometallic Au or Pd catalysts, supported bimetallic Au−Pd nanoparticle catalysts, especially Au2‐Pd2/3DOM Al2O3, show higher catalytic activity for soot combustion due to good synergetic effects between gold and palladium. Au/Pd ratio has a significant influence on the chemical states and size of bimetallic nanoparticles. The co‐presence of Au is favorable for the formation of metallic Pd instead of PdO. And the size of Au−Pd bimetallic nanoparticles gradually decreases with increasing Au/Pd ratio. The effect of water in the reaction atmosphere and SO2‐presulfurization of the catalyst on the activity is also studied. It is unexpected that Au2‐Pd2/3DOM Al2O3 catalysts with SO2‐presulfurization has higher catalytic activity than the fresh catalysts. The increased activity is related to the formed surface aluminum sulfate and enhanced acidity.

Alkali/alkaline-earth metal-modified MnOx supported on three-dimensionally ordered macroporous–mesoporous TixSi1-xO2 catalysts: Preparation and catalytic performance for soot combustion

The performance of catalysts used in after-treatment systems is the key factor for the removal of diesel soot, which is an important component of atmospheric fine particle emissions. Herein, three-dimensionally ordered macroporous–mesoporous TixSi1-xO2 (3DOM-m TixSi1-xO2) and its supported MnOx catalysts doped with different alkali/alkaline-earth metals (AMnOx/3DOM-m Ti0.7Si0.3O2 (A: Li, Na, K, Ru, Cs, Mg, Ca, Sr, Ba)) were prepared by mesoporous template (P123)-assisted colloidal crystal template (CCT) and incipient wetness impregnation methods, respectively. Physicochemical characterizations of the catalysts were performed using scanning electron microscopy, X-ray diffraction, N2 adsorption–desorption, H2 temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed oxidation, and Raman spectroscopy techniques; then, we evaluated their catalytic performances for the removal of diesel soot particles. The results show that the 3DOM-m Ti0.7Si0.3O2 supports exhibited a well-defined 3DOM-m nanostructure, and AMnOx nanoparticles with 10–50 nm were evenly dispersed on the inner walls of the uniform macropores. In addition, the as-prepared catalysts exhibited good catalytic performance for soot combustion. Among the prepared catalysts, CsMnOx/3DOM-m Ti0.7Si0.3O2 had the highest catalytic activity for soot combustion, with T10, T50, and T90 (the temperatures corresponding to soot conversion rates of 10%, 50%, and 90%) values of 285, 355, and 393°C, respectively. The high catalytic activity of the CsMnOx/3DOM-m Ti0.7Si0.3O2 catalysts was attributed to their excellent low-temperature reducibility and homogeneous macroporous–mesoporous structure, as well as to the synergistic effects between Cs and Mn species and between CsMnOx and the Ti0.7Si0.3O2 support.

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.

High-efficient non-noble metal catalysts of 3D ordered macroporous perovskite-type La2NiB’O6 for soot combustion: Insight into the synergistic effect of binary Ni and B’ sites

Double perovskite-type La2NiB’O6 (B’=Mn, Fe, Co, Cu) catalysts with three-dimensional ordered macroporous (3DOM) structure were synthesized by colloidal crystal template method. 3DOM structure promotes the contact efficiency between soot and catalyst. The periodic arrangement of [NiO6] and [B’O6] octahedrons in La2NiB’O6 induces the formation of coordination unsaturated B-site ions. 3DOM La2NiB’O6 catalysts exhibited super catalytic performance for soot combustion under the simulated exhaust, and their catalytic performances are dependent on the synergistic effect of binary Ni and B'-site ions. 3DOM La2NiCoO6 catalyst had the highest catalytic activity for soot combustion, i.e., its T50, SCO2m, TONs and TOFOv values are 362 °C, 98.2 %, 7.80 and 0.151 h−1, respectively. The mechanism was proposed that the synergistic effect of Ni and B’ ions boosts the key step of NO oxidation to NO2. It is meaningful for the development of the non-precious metal catalysts during soot combustion.

Influence of Different Birnessite Interlayer Alkali Cations on Catalytic Oxidation of Soot and Light Hydrocarbons

A series of layered birnessite (AMn4O8) catalysts containing different alkali cations (A = H+, Li+, Na+, K+, Rb+, or Cs+) was synthesized. The materials were thoroughly characterized using X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, Raman spectroscopy, specific surface area analysis, work function, thermogravimetry/differential scanning calorimetry, and transmission electron microscopy. The catalytic activity in soot combustion in different reaction modes was investigated (tight contact, loose contact, loose contact with NO addition). The activity in the oxidation of light hydrocarbons was evaluated by tests with methane and propane. The obtained results revealed that alkali-promoted manganese oxides are highly catalytically active in oxidative reactions. In soot combustion, the reaction temperature window was shifted by 195 °C, 205 °C, and 90 °C in tight, loose + NO, and loose contact conditions against uncatalyzed oxidation, respectively. The catalysts were similarly active in hydrocarbon combustion, achieving a 40% methane conversion at 600 °C and a total propane conversion at ~450 °C. It was illustrated that the difference in activity between tight and loose contacts can be successfully bridged in the presence of NO due to its facile transformation into NO2 over birnessite. The particular activity of birnessite with H+ cations paves the road for the further development of the active phase, aiming at alternative catalytic systems for efficient soot, light hydrocarbons, and volatile organic compounds removal in the conditions present in combustion engine exhaust gases.

Enhancement of the Generation and Transfer of Active Oxygen in Ni/CeO2 Catalysts for Soot Combustion by Controlling the Ni-Ceria Contact and the Three-Dimensional Structure.

The effect of the three-dimensionally ordered macroporous (3DOM) structure and the Ni doping of CeO2 on the physicochemical properties and catalytic activity for soot combustion was studied. Moreover, the way in which Ni is introduced to the ceria support was also investigated. For this, CeO2 supports were synthesized with uncontrolled (Ref) and 3DOM-structured morphology, and their respective Ni/CeO2 catalysts were prepared by impregnation of the previously synthesized supports or by successive impregnation of both precursors (Ni and Ce) on the 3DOM template. Conclusions reached in this study are: (1) the 3DOM structure increases the surface area of the catalysts and improves the catalyst-soot contact. (2) The doping of CeO2 with Ni improves the catalytic activity because the NiO participates in the catalytic oxidation of NO to NO2, and also favors the production of active oxygen and the catalyst oxygen storage capacity. (3) Ni incorporation method affects its physicochemical and catalytic properties. By introducing Ni by successive infiltration in the solid template, the CeO2 crystal size is reduced, Ni dispersion is improved, and the catalyst reducibility is increased. All of these characteristics make the catalyst synthesized by successive infiltration to have higher catalytic activity for soot combustion than the Ni-impregnated CeO2 catalyst.

Boosting the Removal of Diesel Soot Particles by the Optimal Exposed Crystal Facet of CeO2 in Au/CeO2 Catalysts.

Optimized surface facet of the catalysts is an efficient strategy to boost catalytic purification of diesel soot as important components of atmospheric fine particles. Herein, we have elaborately constructed the nanocatalysts of Au nanoparticles supported on the well-defined CeO2 (rod, cube, and polyhedron) with predominantly exposed facets of {110}, {100}, and {111}, respectively. The strong interaction between Au and CeO2 with the optimal crystal facet is crucial to adjust the active site density for activated O2, and the synergy effect of Au and the CeO2{110} facet possesses the largest density of active sites compared with other crystal facets of {100} and {111}. The catalytic activity for soot combustion was tuned by exposed crystal facets of CeO2. The Au/CeO2-rod catalyst exhibits the highest catalytic activity (T50 = 350 °C, TOF = 0.18 h-1) and the lowest apparent activation energy (72 kJ mol-1) during soot combustion. Based on the results of in situ Raman spectra, the formation and stability of oxygen vacancy located at the interface of the Au-O-Ce bond, boosting the key step of NO oxidation to NO2, are dependent on the exposed crystal facets of CeO2. It highlights a new strategy for the fabrication of high-efficient CeO2-based catalysts for the removal of soot particles or other pollution.

Impact of the support on the catalytic activity of Ag nanoparticles for soot combustion

This study investigates the catalytic activity for soot combustion of Ag nanoparticles dispersed on various supports showing different redox properties. Temperature programmed soot oxidation and isotopic exchange experiments were performed to assess the impact of the soot/catalyst contact, the oxygen partial pressure and the ageing toward activity. Three different contact modes have been used to clearly highlight the catalytic performances: loose, tight and supertight. Whatever the support, in both loose and tight contact modes, the catalytic performances are linked with the Ag surface concentration which was found to be high on zirconia-based catalysts and low on ceria-zirconia. The ignition of the soot combustion process occurs on Ag nanoparticles except for catalysts supported on Yttria-Stabilized Zirconia (YSZ), a pure oxygen ionic conductor, where Ag nanoparticles only promote the run-away of the reaction at higher temperatures. Catalysts based on SiO2, ZrO2 and YSZ exhibit a remarkable hydrothermal stability as performances in tight contact mode are fairly similar after the hydrothermal ageing.

Study of Ce/Pr ratio in ceria-praseodymia catalysts for soot combustion under different atmospheres

The effect of Ce/Pr ratio on ceria-praseodymia on structural and surface properties is studied. The catalytic activity towards soot combustion under NOx/O2 and O2/N2 atmospheres is also evaluated, together with the NO oxidation activity to NO2. CexPr1-xO2-δ compositions (x = 0.8, 0.5 and 0.2) have been prepared along with ceria and praseodymia. Catalysts were prepared by co-precipitation. The Ce0.5Pr0.5O2-δ composition, was also prepared by nitrate calcination. Ceria-praseodymia mixed oxides yield reduction profiles shifted to lower temperatures, higher NO oxidation activities to NO2 and improved catalytic activities for soot combustion with respect to pure ceria. Ce0.5Pr0.5O2-δ was the most active one. Under NOx/O2, it has greater soot combustion activity if it is prepared by nitrate calcination. However, under O2/N2, the co-precipitation method is more favorable because of the better dopant insertion achieved in the ceria lattice, which seems to lead better oxygen mobility on the surface and in the bulk oxide.

Highly Active Monolith Catalysts of LaKCoO3 Perovskite-type Complex Oxide on Alumina-washcoated Diesel Particulate Filter and the Catalytic Performances for the Combustion of Soot

The LaKCoO3/ɤ-Al2O3/cordierite and LaCoO3/ɤ-Al2O3/cordierite monolithic catalysts were successfully prepared by impregnating the as-pretreated monolith with aqueous solution of metal salts on monolithic cordierite substrate with a dip-coating two-step method. For comparison, one-step method without the alumina sol coating was also investigated. The monolithic catalysts were characterized by means of XRD, FT-IR, BET, ICP, TG–DSC, XPS and SEM-EDS. The characterization results demonstrate the formation of a small amount of Co3O4 when a large amount of K+ was introduced into LaCoO3 for the substitution of La3+. The coating of porous hollow aluminum oxide nano-particles could enhance the surface area of monolithic cordierite by about 100 times. The active components of LaKCoO3/ɤ-Al2O3 supported catalysts can disperse on the surface of the catalysts as monolayer and be the uniform distributions of La, Co and K. The ultrasonic vibration treating results indicated that the Al2O3 washcoat and catalyst components were adhered to the substrate strongly, the average weight loss is limited to about 1.0 % of the washcoat weight after 30 min in ultrasonic bath. The TG–DSC results show the good thermal stability of the LaKCoO3 and LaCoO3 coatings on alumina-coated monolithic cordierite. The LaKCoO3/ɤ-Al2O3/cordierite catalyst gave the highest catalytic activity for soot combustion among the studied catalysts. The T10, T50, T90 over the LaKCoO3/ɤ-Al2O3/cordierite catalyst were 186.3 °C, 314.6 °C, 390.0 °C, respectively, and Sco2mwas 99.8%.

Three-dimensional ordered macroporous perovskite-type La1–xKxNiO3 catalysts with enhanced catalytic activity for soot combustion: the Effect of K-substitution

Three-dimensional ordered macroporous (3DOM) La1–xKxNiO3 perovskite-type catalysts were successfully prepared by a colloidal crystal template method and characterized by scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray scattering elemental mapping, X-ray diffraction, Raman and X-ray photoelectron spectroscopy, and temperature-programmed reduction of H2. Further, their catalytic activity in soot combustion was determined by temperature-programmed oxidation reaction. K substitution into the LaNiO3 lattice led to remarkably improved catalytic activity of this catalyst in soot combustion. Amongst various catalysts, La0.95K0.05NiO3 exhibited the highest activity in soot combustion (with its T50 and values being 338 °C and 98.2%, respectively), which is comparable to the catalytic activities of Pt-based catalysts under the condition of poor contact between the soot and the catalyst. K-substitution improves the valence state of Ni and increases the number of oxygen vacancies, thereby leading to increased density of surface-active oxygen species. The active oxygen species play a vital role in catalyzing the elimination of soot. The perovskite-type La1–xKxNiO3 nanocatalysts with 3DOM structure without noble metals have potential for practical applications in the catalytic combustion of diesel soot particles.

In situ exsolution of Co/CoOx core-shell nanoparticles on double perovskite porous nanotubular webs: A synergistically active catalyst for soot efficient oxidation

The PrBa0.5Sr0.5Co0.2Fe1.8O5+δ double perovskite porous nanotubular webs are prepared by a simple electrospinning technique following calcination. It shows better catalytic activity compared with the bulk PrBa0.5Sr0.5Co0.2Fe1.8O5+δ prepared by citrate method, due to its larger specific surface area and higher utilization of active sites. On basis of this, introducing multiple active sites is conducive to enhancing the catalytic activity. In this work, the PrBa0.5Sr0.5Co0.2Fe1.8O5+δ double perovskite porous nanotubular webs are further reduced at 750 °C in a 10% H2/N2 gas flow, which can give rise to the in situ exsolution of Co core-shell nanoparticles and obtain double active sites. Meanwhile, series of related catalysts are also prepared for comparison, and the physicochemical properties of these catalysts are studied by a lot of characterization techniques. The catalytic performance for soot combustion is evaluated by a temperature programmed oxidation test, which can simulate the soot combustion process. Turn of frequency (TOF) and activation energy (Ea) are calculated by isothermal studies to further evaluate the activity of the as-prepared catalyst. Among all the prepared catalysts, the PrBa0.5Sr0.5Co0.2Fe1.8O5+δ porous nanotubular webs after reductive treatment at 750 °C in H2 atmosphere exhibits the best catalytic activity for soot combustion, showing the lowest activation energy and the highest TOF values. Furthermore, its catalytic activity is significantly promoted compared with the bulk-type catalyst. Firstly, it may be associated with the synergistic effects of sufficient Co core-shell nanoparticles and oxygen vacancies in double perovskite functioned as active sites. Secondly, the structure of porous nanotubular webs can make full use of these active sites.

SrTi1−XMnXO3 and MnOX/SrTiO3 with dendritic morphology: A comparison of physico-chemical properties and soot catalytic combustion

Abstract In this work, a comparative study of the physico-chemical and catalytic properties of doped and impregnated Mn-SrTiO3 for the catalytic combustion of soot has been reported. Results show that SrTiO3 demonstrated dendritic morphology that is attributed to SrTiO3 with perovskite structure. XPS analysis confirmed the successful incorporation of Mn4+ species in Ti4+ lattice sites for doped samples, whereas different MnOX species were formed on the surface of SrTiO3 in the case of impregnated catalysts with different Mn loadings. Among all catalysts tested in this work, samples doped with 1 wt% Mn showed the best catalytic behavior, decreasing the combustion temperature well above 100 °C compared with the uncatalyzed reaction and a Mn-turnover number of 5.77 which is comparable with previous perovskite reports. During the soot catalytic combustion process, accelerated oxidation rates were observed at high temperatures. This may be attributed to the mobility of the bulk oxygen reaching the catalyst surface, promoted by the high redox capacity of Mn-doped perovskites. Despite a reduction in the Mn species observed for MnOx impregnated samples, they showed much less catalytic activity when compared with the doped samples because of the strong contribution of bulk oxygen in the perovskite structure. These doped catalysts also displayed low catalytic activity at temperatures below 500 °C, which is possibly due to the presence of surface carbonates. This work contributes to the idea that bulk oxygen plays an important role in perovskites as a catalyst that provides enhanced catalytic activity for soot combustion.

Decorating CeO2 Nanoparticles on Mn2O3 Nanosheets to Improve Catalytic Soot Combustion

Herein, we synthesized CeO2 nanoparticles-decorated Mn2O3 nanosheets on monolithic Ni foam (Ce/Mn-NF) for catalytic elimination of soot particulates. The macroporous nanostructures created by the Mn2O3 nanosheets improve the soot-catalyst contact efficiency on the external surface of catalysts. The superficial Mn–Ce interaction can produce Mn4+ and oxygen vacancies on the Ce/Mn-NF catalysts through the redox process of Ce4+ + Mn3+ ↔ Mn4+ + Ce3+, simultaneously generating surface active oxygen species. Moreover, our results demonstrate that the surface adsorbed oxygen species induced by the Mn–Ce interaction are more active for catalytic soot oxidation than those on the Mn-NF. Thus, the introduction of the CeO2 nanoparticles to the Mn2O3 nanosheets can significantly improve the catalytic activity for soot combustion. For the Ce/Mn-NF-2, the surface atomic ratio of Ce and Mn is close to 1:1, which will create more Mn–Ce interaction sites to generate active oxygen species compared with other catalysts. Accor...

Nanostructured Potassium-Manganese Oxides Decorated with Pd Nanoparticles as Efficient Catalysts for Low-Temperature Soot Oxidation

Two nanostructured potassium–manganese oxides, with a layered (OL) and tunneled structure (OMS-2), were synthesized and their surface decorated with 1% Pd. All prepared samples were characterized by means of X-ray diffraction, Raman spectroscopy, N2-BET specific surface area analysis, TPR, SEM/TEM. Catalytic activity in soot combustion in different reaction conditions was investigated (tight contact, loose contact, loose contact with NO addition). The obtained results revealed, that manganese oxides are highly catalytically active in soot combustion, shifting the reaction temperature window by 280 °C for OMS-2 and 300 °C for OL in comparison to the non-catalytic process. Furthermore, Pd promotion is beneficial in all cases, lowering the window of soot combustion compared to the unpromoted oxides, with the most significant effect for loose contact conditions. The difference in activity between tight and loose contacts can be successfully bridged in the presence of NO due to its transformation into NO2. The particular activity of 1% Pd/OMS-2 and 1% Pd/OL pave the road for their further development towards catalytic system for efficient soot removal in the conditions present in diesel exhaust gases.Graphical

Cobalt deposited on micro and nanometric structures of ceria and zirconia applied in diesel soot combustion

Two series of shaped catalysts were obtained, one of them from CeO2 and the other one from ZrO2, to which cobalt was added. On the one hand, ceria fibers prepared by electrospinning exhibited greater catalytic activity for soot combustion, under loose contact and in the presence of NO, than those made by hydrothermal synthesis. The deposition of low loads of cobalt (2 wt.%) resulted in a positive effect for soot combustion (maximum soot combustion rate, TM = 360 °C), whereas higher loadings (12 wt.%) did not result in a further improvement. On the other hand, cobalt catalysts supported on zirconia nanorods were prepared by hydrothermal synthesis. In comparison with the ceria catalysts, zirconia showed a better catalytic activity when the cobalt load increased from 2 to 12 wt.%, due to a better dispersion of cobalt on ZrO2. This is in line with STEM and EDX results that indicated the presence of smaller aggregates of cobalt on the zirconia surface. Among the ZrO2 catalysts studied, Co(12%)-ZrO2 presented the best catalytic activity (TM = 360 °C), obtained under loose contact conditions and in the presence of NO. The activity of the catalysts was thoroughly correlated with the characterization of the samples by XRD, SEM, EDX, STEM, LRS and XPS.

Catalytic Oxidation of Soot on a Novel Active Ca-Co Dually-Doped Lanthanum Tin Pyrochlore Oxide.

A novel active Ca-Co dually-doping pyrochlore oxide La2−xCaxSn2−yCoyO7 catalyst was synthesized by the sol-gel method for catalytic oxidation of soot particulates. The microstructure, atomic valence, reduction, and adsorption performance were investigated by X-ray powder diffraction (XRD), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), H2-TPR (temperature-programmed reduction), and in situ diffuse reflection infrared Fourier transformed (DRIFTS) techniques. Temperature programmed oxidation (TPO) tests were performed with the mixture of soot-catalyst under tight contact conditions to evaluate the catalytic activity for soot combustion. Synergetic effect between Ca and Co improved the structure and redox properties of the solids, increased the surface oxygen vacancies, and provided a suitable electropositivity for oxide, directly resulting in the decreased ignition temperature for catalyzed soot oxidation as low as 317 °C. The presence of NO in O2 further promoted soot oxidation over the catalysts with the ignition temperature decreased to about 300 °C. The DRIFTS results reveal that decomposition of less stable surface nitrites may account for NO2 formation in the ignition period of soot combustion, which thus participate in the auxiliary combustion process.