Treatment of exhaust gases from a methanol fueled vehicle over perovskite oxide catalysts

As a study on the treatment of exhaust gases from a methanol-fueled vehicle, catalytic oxidation of formaldehyde and methanol on perovskite-type oxides was performed. La_0.8Sr_0.2MnO₃, La_0.8Sr_0.2CoO₃, YBa₂Cu₃O₇ (superconductor), and ErBa₂Cu₃O₇ (superconductor) were used as catalysts. La-based catalysts were prepared by a citrate method and calcined at 650°C, 800°C, and 900°C, respectively. The catalytic activity of La-based catalysts increased with the increase in the surface area that was dependent on the calcination temperature. Superconductive oxides were also prepared by a citrate method and calcined at 920°C. The catalytic activity of ErBa₂Cu₃O₇ was found to be better than that of YBa₂Cu₃O₇. For La-based perovskite calcined at 650°C, the catalytic activity of La_0.8Sr_0.2MnO₃ was higher than La_0.8Sr_0.2CoO₃. Calcining at 800°C and 900°C, however, the catalytic activity of LLa_0.8Sr_0.2 CoO₃ was higher than La_0.8Sr_0.2MnO₃.     

Enhancing p-xylene productivity for disproportionation of toluene in microstructured reactors

Microstructured monolith reactors washcoated with ZSM5 and La₂O₃-loaded ZSM5 (LaZSM5) were used for disproportionation of toluene for studying the effect of washcoat thickness on reactor productivity and yield of the commercially important p-xylene isomer. The toluene conversion and p-xylene yield in the ZSM5 washcoated monolith reactor was superior to that in a packed bed reactor using ZSM5 pellets. Modification of the surface properties of ZSM5 due to addition of La₂O₃ reduced the toluene conversion but resulted in a substantial enhancement in p-xylene yield. The decrease in catalytic activity and p-xylene yield with increase in washcoat thickness was attributed to the lengthening of the diffusional path length. The reactor productivity was highest with thin washcoats and low conversion on La₂O₃-loaded ZSM5 washcoated monoliths. The advantage of higher p-xylene productivity using monoliths is offset by the increase in the cost of recycling unreacted toluene.     

Electrochemical characterization of La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>MnO<Subscript>3</Subscript>-coated NiO as cathodes for molten carbonate fuel cells

La_0.8Sr_0.2MnO₃ was coated on porous NiO cathode using a simple combustion process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed in the cathode characterizations. The electrochemical behavior of La_0.8Sr_0.2MnO₃-coated NiO cathodes (LSM–NiO) were also evaluated in a molten 62 mol%Li₂CO₃+38 mol%K₂CO₃ eutectic at 650 °C under the standard cathode gas condition by electrochemical impedance spectroscopy (EIS). The impedance response of the NiO and LSM–NiO cathode at different immersion times is characterized by the presence of depressed semicircles in the high frequency range and an extension at low frequencies. Impedance analysis showed that the behavior of the developed cathode was similar to that of the conventional nickel oxide cathode. The LSM–NiO showed a lower dissolution and a better catalytic efficiency superior to the state-of-the-art NiO value. Thus the cathode prepared with coating method to coat La_0.8Sr_0.2MnO₃ on the surface of NiO cathode is able to reduce the solubility of NiO to lengthen the lifetime of MCFC while maintaining the advantages of NiO cathode. The LSM–NiO shows promise as an alternate cathode in molten carbonate fuel cells (MCFCs).     

Tailoring La0.8Sr0.2MnO3/La/Sr nanocomposite using a novel complementary method as well as dissecting its microwave,shielding, optical,and magnetic characteristics

In this work, a novel approach was introduced to reduce the oxide nanoparticles and extract the pure metal from them. Accordingly, La_0.8Sr_0.2MnO₃ nanoparticles were prepared through the conventional citrate gel method, and then they were reduced using a solvothermal method by ethylene glycol as a reductive agent. Chemical species, magnetic parameters, crystal structures, and morphological properties of the fabricated structures were deeply studied by Fourier transform infrared (FT-IR), vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), and field emission scanning electron microscopy (FE-SEM) analyses, respectively. Noticeably, the curves of the diffuse reflection spectroscopy (DRS) suggested a lower energy gap for the La_0.8Sr_0.2MnO₃/La/Sr nanocomposite. Finally, the microwave absorbing characteristics of the specimens were scrupulously investigated using the polystyrene (PS) and polyvinylidene fluoride (PVDF) media. It was found that La_0.8Sr_0.2MnO₃/La/Sr blended in PVDF gained a remarkable reflection loss of 94.68 dB at 15.31 GHz with an only thickness of 1.75 mm, meanwhile displaying an efficient bandwidth as wide as 6.74 GHz (reflection loss (RL) > 10 dB). Noteworthy, La_0.8Sr_0.2MnO₃/PS illustrated a considerable efficient bandwidth of 2.36 GHz (RL > 20 dB). Moreover, La_0.8Sr_0.2MnO₃ composites demonstrated more than 88% electromagnetic interference shielding efficiency (SE) along the X and Ku-band frequency.     

NO SCR reduction by hydrogen generated in line on perovskite-type catalysts for automotive diesel exhaust gas treatment

This paper deals with the preparation (by solution combustion synthesis, SCS), characterization (by XRD, BET, FESEM and TPD/R analyses), catalytic activity evaluation (in a temperature-programmed reaction—TPRe apparatus), and the assessment of the reaction mechanism of NO reduction by H₂ in the presence of oxygen on a series of perovskite-type catalysts belonging to the LaFeO₃ family (LaFeO₃, La_0.8Sr_0.2FeO₃, Pd/La_0.8Sr_0.2FeO₃, La_0.8Sr_0.2Fe_0.9Pd_0.1O₃, La_0.7Sr_0.2Ce_0.1FeO₃, Pd/La_0.7Sr_0.2Ce_0.1FeO₃, La_0.7Sr_0.2Ce_0.1Fe_0.9Pd_0.1O₃). The catalysts have been studied in the 25-350 °C temperature range. Significant catalytic activities were measured at 150-250 °C. Among the catalysts screened, La_0.8Sr_0.2Fe_0.9Pd_0.1O₃, showed the best performance. Hence, it was deposited directly over a ceramic honeycomb monolith by in situ SCS and then tested in a lab-scale test rig. A mechanistic analysis is presented concerning the relationship between the observed activity and the reducibility of the B site, determined from TPR experiments, as well as the correlation between the observed oxygen inhibition and the proposed NO_x reduction mechanism.Some final conclusions are drawn on the perspective of the practical application of the investigated after-treatment route for diesel exhaust gases.     

Development of Monolithic Catalysts with Low Noble Metal Content for Diesel Vehicle Emission Control

Monolith washcoated catalysts with potential for diesel emission control have been developed. Two types of catalysts have been prepared for further study: (1) MnO _x supported on granulated -Al₂O₃, (2) MnO _x supported on cordierite monolith washcoated with -Al₂O₃. Both catalysts have been calcined at 500 and 900 °C and subsequently modified by doping with 0.1–1.0 wt% of Pt or Pd. The influence of the concentration of both manganese oxide (0–10 wt%) and noble metals Pt and Pd in the range 0–1.0 wt% on the catalytic activity in methane oxidation has been studied. Comparison of the catalytic activity of MnO _x /Al₂O₃ and MnO _x + Pt(Pd)/Al₂O₃ with that of a standard 1 wt%Pt/Al₂O₃ catalyst shows the existence of a synergetic effect. This effect is more pronounced for the samples calcined at 900 °C. The developed monolithic catalysts MnO _x + Pt(Pd)/Al₂O₃ demonstrate higher activity and thermal stability (up to 900 °C) compared to the commercial monolithic catalyst (TWC's).     

Enhanced high temperature microwave absorption of La0.9Sr0.1MnO3/MgAl2O4 composite ceramics based on controllable electrical conductivity

The high temperature microwave absorbing efficiency (HTMAE) of xLa_0.9Sr_0.1MnO₃/(1 − x)MgAl₂O₄ composite ceramics was investigated by studying the crystal structure, electrical conductivity, and permittivity. The crystal structure of La_0.9Sr_0.1MnO₃ and MgAl₂O₄ were maintained, but the Mn³⁺ and Al³⁺ ions were exchanged with each other through doping. The conductivity and permittivity of the composite ceramics increased with the increase of La_0.9Sr_0.1MnO₃ content and test temperature. When x = 0.36, the electrical conductivity in La_0.9Sr_0.1MnO₃ significantly enhanced the microwave polarization of the composite ceramics at high temperature. According to transmission/reflection modelling, the composite ceramics with x = 0.24 showed excellent HTMAE near the optimal thickness of 1.8 mm. Although the optimal thickness of the composite with x = 0.36 was reduced to 1.1 mm, the HTMAE was seriously lessened due to an impedance mismatch. xLa_0.9Sr_0.1MnO₃/(1 − x)MgAl₂O₄ are promising as thin and efficient microwave absorbing materials at high temperatures and the microwave permittivity can be further enhanced by adjusting the conductivity of La_0.9Sr_0.1MnO₃.     

Au改性La0.8Sr0.2MnO3催化剂的催化燃烧性能

采用共沉淀（CP）和沉积-沉淀法（DP）分别制备了0.5%(质量分数)金掺杂的Au-LSM和Au/LSM钙钛矿催化剂,以甲苯催化燃烧为模型反应测试催化剂活性,并用XRD、BET、H₂-TPR对其进行表征。结果表明,Au掺杂并不改变La_0.8Sr_0.2MnO₃催化剂的织构性质,但明显增强了催化剂表面氧的活动性,提高了其低温催化氧化活性。与DP法制备的Au/LSM相比,Au-LSM表现出更好的催化性能,其催化活性与商业贵金属Pd/Al₂O₃相当。通过对焙烧温度考察以及50 h的变温活性测试,Au-LSM催化性能并没有发生较大变化,催化剂具有良好的稳定性。     

Electrochemical performance of La0.8Sr0.2MnO3 oxygen electrode promoted by Ruddlesden-Popper structured La2NiO4

The effects of introducing La₂NiO₄ nanocatalyst on the electrochemical performance of La_0.8Sr_0.2MnO₃ are investigated under solid oxide electrolysis cell and fuel cell modes, as well as open circuit voltage. Extracted data from impedance spectroscopy are interpreted with the analysis of distribution of relaxation times. La₂NiO₄ infiltration effectively reduces the activation energy of the oxygen reactions from 1.35 to 0.99 eV. It also changes the rate controlling process of the overall reaction. Polarization behavior of La₂NiO₄-infiltrated La_0.8Sr_0.2MnO₃ electrode shows superior performance under electrolysis mode compared to the fuel cell mode. Drastic increase in the size of low frequency arc during anodic current passage in the non-infiltrated La_0.8Sr_0.2MnO₃ electrode is hampered by infiltration of La₂NiO₄ nanocatalyst. By applying anodic current on infiltrated La_0.8Sr_0.2MnO₃, no displacement is observed in the position of high frequency peaks in the distribution of relaxation time graphs and only a small increase in height occurs for the low frequency arc. Additionally, La₂NiO₄-infiltrated electrode impressively decreases overpotential by 74% compared to the non-infiltrated one under electrolysis mode at 800°C.     

Low-temperature synthesis of La0.6Sr0.4Co0.2Fe0.8O3−δ perovskite powder via asymmetric sol–gel process and catalytic auto-combustion

La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ powder was synthesized by a combined EDTA-citrate complexing process via low-temperature auto-combustion synthesis with NH₄NO₃ as an oxidizer and a combustion trigger. Two novel methods were explored to improve this auto-combustion technology with reduced NH₄NO₃ addition: the use of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ as the combustion catalyst and the application of asymmetric sol–gel process to provide the precursor with different NH₄NO₃ concentrations. The prepared perovskite powder was characterized by BET, SEM, XRD and iodometric titration techniques. The catalytic performance of the powder was also examined in the decomposition of peroxide hydrogen. Experimental results indicate that powders from catalytic combustion and asymmetric precursor routes have more advantages in terms of better crystallites, higher specific surface area, higher B-site valence state, improved sintering capability and better catalytic performance in peroxide hydrogen decomposition than that from the synthesis with uniform NH₄NO₃ distribution.     

Electrical and magnetic properties of La1−xSrxMnO3 (0.1 ≤ x≤ 0.25) ceramics prepared by sol–gel technique

La_1−xSr_xMnO₃ (0.1 ≤ x ≤ 0.25) high density ceramics were prepared by sol-gel method using methanol as solvent. X-ray diffraction analysis showed that all samples exhibited single perovskite structure and no second phase was detected. Scanning electron microscopy images exhibited good particle connectivity on the surface of sample, and grain size increased with the increase in Sr doping. Resistivity-temperature curves of samples were measured by standard four-probe method, and curves exhibited significant differences in studied range of Sr doping. Magnetic measurement results indicated that the variation of susceptibility of different samples was quite different, and the Curie temperature of samples increased with the increase in Sr content. For x = 0.2, temperature coefficient of resistance value of the sample was larger, and corresponding peak TCR temperature was 307.1 K, which is very close to room temperature. Thus, La_0.8Sr_0.2MnO₃ ceramics exhibited high TCR value close to room temperature. Combined with its excellent magnetic properties, La_0.8Sr_0.2MnO₃ ceramics may potentially act as effective candidates for uncooled radiation calorimeter and uncooled magnetic sensor. Applications of La_0.8Sr_0.2MnO₃ ceramics in uncooled infrared radiation calorimeter at room temperature will be highly beneficial.     

Phase interaction and oxygen transport in oxide composite materials

Abstract

The oxygen permeability of oxide composite membranes containing similar volume fractions of the components, including (La_0.9 Sr_0.1)_0.98 Ga_0.8 Mg_0.2 O_3-δ(LSGM)–La_0.8 Sr_0.2Fe_0.8Co_0.2O_3-δ (LSFC), LSGM–La₂Ni_0.8Cu_0.2O_4+δ (LNC), SrCoO_3-δ–Sr₂Fe₃O_{6.5 ±δ}, Ce_0.8Gd_0.2O_2-δ (CGO)–LSFC and CGO–La_0.7Sr_0.3MnO_3-δ (LSM), was studied at 973–1223 K. In most cases, oxygen transport is substantially affected by component interaction, decreasing ionic conductivity due to cation interdiffusion, and formation of intermediate phases and/or blocking layers at grain boundaries. This interaction is maximised in systems where the phase components have similar structure and thus may form continuous solid solutions, for example LSGM–LSFC, or intermediate compounds such as Roddlesden–Popper phases in LSGM–LNC composites. The results show that, in addition to knowledge of the transport properties and volume fractions of percolating phases, analysis of ionic conduction in oxide composite materials requires assessment of phase interaction and grain boundary processes.     

Nanonickel Particles Supported on Silica. Morphology Effects on Their Surface and Hydrogenating Properties

The combustion of light hydrocarbons finds an important application in volatile organic compounds (VOCs) abatement. Catalytic combustion is interesting in this domain, because it may be carried out at relatively low temperatures and under large air excess. For this purpose, precious metal-based catalysts are very performing, but the quest for a lower-cost alternative solution is necessary. In this field, conducting mixed oxides such as perovskites are good candidates, especially when they are electrochemically promoted. The present work shows that electrochemical promotion of catalytic activity (NEMCA effect) in propene total combustion can be carried out with La_0.8Sr_0.2Co_0.8Fe_0.2O₃, an electron-conducting perovskite-type oxide, deposited on YSZ.     

Catalytic decomposition of nitrous oxide over perovskite type solid oxide solutions and supported noble metal catalysts

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been investigated over various solid oxide solutions (SOS), La_0.8Sr_0.2MO_3– (M=Cr, Fe, Mn, Co or Y), La_1.8Sr_0.2CuO_4– and supported Pd, Pt catalysts. The reaction was carried out in a gradientless recycle reactor at 1 atm pressure with a feed gas containing about 0.5% N₂O (in helium). Among the various solid solutions, La_0.8Sr_0.2CoO_3– showed a maximum N₂O conversion of 90% at 600C. The order of activity observed for N₂O decomposition was La_0.8Sr_0.2CoO_3–>La_0.8Sr_0.2FeO_3–>La_1.8Sr_0.2CuO_4–> La_0.8Sr_0.2MnO_3–La_0.8Sr_0.2CrO_3–La_0.8Sr_0.2YO_3–. The activity of La_0.8Sr_0.2CoO_3– was compared with supported Pd, Pt and also with unsubstituted LaCoO₃ catalysts under similar reaction conditions. Among all the catalysts tested in this study, Pd/Al₂O₃ showed the lowest light-off temperature for N₂O decomposition. The activity of La_0.8Sr_0.2CoO_3– was found to be comparable to Pd/Al₂O₃ catalyst at temperatures above 500 C. The influence of added oxygen (about 4%) in the feed was examined over La_0.8Sr_0.2CoO_3– and Pd/Al₂O₃ catalysts and only in the case of cobalt catalyst was the conversion of N₂O decreased by 13%. By choosing varied sintering conditions, La_0.8Sr_0.2CoO_3– of different BET surface areas were prepared and the light-off temperature was found to decrease with increase in surface area. The results obtained over solid solutions are discussed on the basis of the cation mixed valency and oxygen properties of the catalyst.     

A Study on the Relationship Between Low-Temperature Reducibility and Catalytic Performance of Single-Crystalline La0.6Sr0.4MnO3+δ Microcubes for Toluene Combustion

Single-crystalline La_0.6Sr_0.4MnO_3+δ microcubes of cubic perovskite phase were prepared hydrothermally. The adopted temperature and time of hydrothermal treatment and the amount of KOH used had great effects on the low-temperature reducibility of La_0.6Sr_0.4MnO_3+δ . The initial H₂ consumption rate of La_0.6Sr_0.4MnO_3+δ played a vital role in determining its catalytic activity for toluene combustion. It is concluded that the perovskite-type oxide catalyst with a higher initial H₂ consumption rate displayed a higher catalytic activity for the addressed reaction.     

Single step reactive sintering and chemical compatibility between La9Sr1Si6O26.5 and selected cathode materials

Apatite-type silicates are considered as promising electrolytes for solid oxide fuel cells (SOFC). However more studies on the chemical compatibility of these materials with common SOFC electrodes are required. Here, we report the synthesis of single phase La₉Sr₁Si₆O_26.5 composition by reactive sintering at 1650 °C for 10 h. Fully dense pellets showed very high oxide-anion conductivity, 25 mS cm^?1 at 700 °C. Furthermore, the chemical compatibility of La₉Sr₁Si₆O_26.5 with some selected cathode materials has also been investigated. The lowest reaction temperatures were determined to be 1100 °C, 1000 °C and 900 °C for La_0.8Sr_0.2MnO_3?δ, La₂Ni_0.8Cu_0.2O₄ and La_0.6Sr_0.4Co_0.8Fe_0.2O₃, respectively. The segregation of minor amounts of SiO₂ seems to be a key limiting factor that must be overcome. Finally, these cathode materials were deposited over dense oxy-apatite pellets and the area specific resistances in symmetrical cells were determined. These values, at 700 °C, were 14.4 and 2.6 Ω cm² for La_0.8Sr_0.2MnO_3?δ and La_0.6Sr_0.4Co_0.8Fe_0.2O_3?δ, respectively. Furthermore, the area specific resistances are notably improved 0.6 Ω cm² when a 50 wt.% composite of La_0.6Sr_0.4Co_0.8Fe_0.2O_3?δ and Ce_0.8Gd_0.2O_1.9 is used.     

Electrode materials for intermediate temperature proton-conducting fuel cells

Some electrode materials for intermediate temperature proton-conducting fuel cells are analysed from the perspective of surface reaction and ionic conductivity type. The performance of H₂/O₂ fuel cells using these materials as electrodes with LiNaSO₄–Al₂O₃ as the electrolyte indicates that Ni–Al alloy, Ni–Al₂O₃ catalyst and Ni–YSZ cermet are potential candidates for anode materials and that LiNiO₂, LiCoO₂, Ag–SnO₂ and La_0.8Sr_0.2MnO₃ are good candidates for cathode materials. Among the tested electrode materials, for the same electrolyte, the LiNiO₂/Ni–Al₂O₃ electrode pair gives the best cell performance.     

Synthesis,Characterization, and Catalytic Activity of Mn‐doped Perovskite Oxides for Three‐Way Catalysis

Mn‐doped La_0.8Sr_0.2CoO₃ perovskite oxides (La_0.8Sr_0.2Co_1–xMn_xO₃; x = 0, 0.1, 0.3, 0.5) were synthesized by a modified sol‐gel method. The phase‐pure oxides were obtained. CoO and carbonates were formed on the surface of La_0.8Sr_0.2CoO₃. With increasing doping content, these impurities were reduced while the stability of the perovskite structure was improved. The valence state of B‐site ions and the amount of absorbed oxygen were influenced by Mn doping. The catalytic activity of the perovskite catalysts was investigated for CO oxidation and simultaneous removal of CO, C₃H₈, and NO. For CO and NO removal, La_0.8Sr_0.2Co_0.9Mn_0.1O₃ exhibited the best performance. For C₃H₈ removal, the reactivity was promoted linearly with the doping content. The structure‐activity relationship is also discussed.     

Magneto-caloric properties of La0.8-xSmxSr0.2MnO3 (x=0.0, 0.05, 0.1, and 0.15)

In this work, the manganite's magnetocaloric properties are studied by changing their chemical composition for a group La_0.8-xSm_xSr_0.2MnO₃ (x = 0.0, 0.05, 0.10, and 0.15) ceramic synthesized by the solid-state reaction method. According to the X-ray powder diffraction (XRD) analysis, no sign of a secondary phase is detected. It is found that the prepared samples are formed in the rhombohedral crystal structure with an R-3c space group. There is a decreasing trend in the unit cell volume, which indicates the gradual replacement of Sm in La sites. The results obtained from the energy-dispersive X-ray (EDAX) spectroscopy test indicated that the ratio of elements in the compounds is close to their nominal values. Based on the M measurements (upon the change of temperature) of the as-prepared specimens, an FM transition is observed. The transition temperature decreases upon the increase of the x value. The measured magnetic entropies of all the La_0.8-xSm_xSr_0.2MnO₃ samples are an illustration of a magnetocaloric impact on these compounds. This observation introduces La_0.8-xSm_xSr_0.2MnO₃ as a potential candidate for applications related to magnetic refrigeration.     

Combination of Ag/Al2O3 and Fe-BEA for High-Activity Catalyst System for H2-Assisted NH3-SCR of NO x for Light-Duty Diesel Car Applications

Low-temperature active Ag/Al₂O₃ and high-temperature active Fe-BEA zeolite were combined and tested for H₂-assisted NH₃-selective catalytic reduction (SCR) of NO _x . The catalysts were either washcoated onto separate monoliths that were placed up- or downstream of each other (dual-brick layout) or washcoated on top of each other in a sandwiched layout (dual-layer). Our results showed that it is highly preferred to have Ag/Al₂O₃ as the upstream or outer layer catalyst. Fe-BEA showed a high NH₃ oxidation giving an NH₃ deficit over the Ag/Al₂O₃. Ag/Al₂O₃ formed NO₂ which enhanced the activity over Fe-BEA through the “fast”-SCR reaction when Fe-BEA was placed downstream or as inner layer. When no H₂, which is needed for the SCR reaction over Ag/Al₂O₃, was added, the dual-layer layout was preferred. The shorter diffusion distance between the layers is a probable explanation.