The influence of alkali metal cations in substituted nanostructured LaCoO3 on oxidation catalytic activity (original) (raw)
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Manganese Oxide Promoted LACOO3 Nano-Perovskite for Oxidation of a Model Exhaust Gas
2012
Catalysts with the formula of LaCoMnxO(3+a), where x is 0.0, 0.2, 0.3 and 0.5 were studied for CO and C2H6 oxidation. Ethane was selected as a model for hydrocarbon combustion. Samples were prepared by the citrate method and calcined at 600 o C for 8 h. Prepared catalysts were characterized by FT-IR, XRD, SEM, TEM, TPR and EDS analyses. Structural studies show that the manganese oxide addition up to 0.5 mol, i.e. 50%, has no effect on the LaCoO3 perovskite phase formation. Crystallite size of different phases, comprising perovskite and manganese oxide, was determined by the Scherrer equation. Addition of 0.3 mol manganese was observed to improve the catalytic property of the lanthanum cobaltite; oxidizes the CO and hydrocarbons at lower temperature.
Industrial & Engineering Chemistry Research, 2011
Perovskite-type La 1Àx K x CoO 3 and LaCo 1Ày Fe y O 3 catalysts were prepared and characterized by nitrogen sorption, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. Catalytic activity for the simultaneous removal of NO x and soot was investigated using temperatureprogrammed reactions. For the La 1Àx K x CoO 3 series, the introduction of K ions into the A-site caused the enhancement of Co valence state, which was beneficial to improving the catalytic activity. Excess K ions produced a Co 3 O 4 phase adhering to the perovskite crystals, but the rhombohedral perovskite structure was well-maintained. In contrast, the B-site could be substituted by Fe ions with the doping ratio changing from null to 0.5, and no secondary phases were detected. With increasing K substitution, NO x conversion in the La 1Àx K x CoO 3 series showed a declining trend after an initial ascent. The Co 3 O 4 particles produced at high K content were responsible for this falling catalytic activity. For the LaCo 1Ày Fe y O 3 series, catalytic performances showed a monotonously decreasing trend as a function of Fe substitution. Among all of the perovskite oxides tested in this study, the La 0.6 K 0.4 CoO 3 sample exhibited the highest catalytic activity for the simultaneous removal of NO x and soot.
Ba-doped vs. Sr-doped LaCoO3 perovskites as base catalyst in diesel exhaust purification
Molecular Catalysis, 2020
Perovskites (ABO 3) have emerged in recent years as an economic alternative to noble metals for oxidationreduction reactions in diesel engines aftertreatment systems. Sr-doped La 1-x Sr x CoO 3 perovskites have shown high efficiency in NO oxidation and limited NO x reduction efficiency. Alternatively, in this work, the effects of barium doping on NO x removal efficiency of LaCoO 3 perovskite are explored with the aim of developing a more promising perovskite base catalyst. Bulk perovskites were prepared by substituting La 3+ with increasing Ba 2+ doping levels, i.e. La 0.9 Ba 0.1 CoO 3 , La 0.8 Ba 0.2 CoO 3 , La 0.7 Ba 0.3 CoO 3 , La 0.6 Ba 0.4 CoO 3 and La 0.5 Ba 0.5 CoO 3. The prepared catalysts were characterized in terms of crystalline structures identification (XRD), specific surface area (N 2 adsorption-desorption at-196°C), reducibility and oxidation state of Co ions (H 2-TPR), concentration and strength of adsorbed oxygen species (O 2-TPD) and surface basicity (CO 2-TPD). The characterization results suggest that charge imbalance associated to Ba 2+ accommodation in the perovskite lattice in substitution of La 3+ leads to a preferential formation of oxygen vacancies. As a result, Ba-doped perovskites improve NO-to-NO 2 conversion with respect to LaCoO 3 perovskite. La 0.7 Ba 0.3 CoO 3 perovskite shows the best NO oxidation efficiency (66 % at 350°C). This fact is associated to the higher oxygen vacancies concentration, which favors the exchange capacity between oxygen in the lattice and in the gas phase. This sample also shows the best NO x storage and reduction efficiency (maximum NO x-toN 2 reduction of 40 % at 350°C). On the one hand, NO x adsorption is promoted due to the best balance between NO oxidation capacity and NO x adsorption sites accessibility. On the other hand, the higher strength of NO x adsorption sites promotes a slower nitrates decomposition, which favors NO x reduction during rich period. The obtained results improve the NO x removal efficiency of reference La 0.7 Sr 0.3 CoO 3 sample (maximum NO x-toN 2 reduction of 10 % at 350°C). Thus, La 0.7 Ba 0.3 CoO 3 catalyst is considered as a more promising base material for automotive applications.
La0.9Ba0.1CoO3 perovskite type catalysts for the control of CO and PM emissions
Catalysis Communications, 2010
Perovskite type catalysts with LaCoO 3 and La 0.9 Ba 0.1 CoO 3 compositions have been prepared by sol-gel method and their catalytic activity was studied for CO oxidation in presence of CO 2 , water and also for particulate matter (PM)/carbon oxidation. The catalysts were characterized using XRD, BET-SA, SEM, TPD, XPS and their catalytic activity was evaluated using a steady state gas evaluation assembly, as well as thermo gravimetric analysis. La 0.8 Ba 0.1 CoO 3 catalyst shows enhanced catalytic activity as compared to LaCoO 3 for CO and PM oxidation. Barium substitution appears to be responsible for low temperature activity of the catalyst by influencing redox and oxygen desorption properties as also suggested by TPD studies.
Alumina-supported LaCoO3 perovskite for selective CO oxidation (SELOX)
International Journal of Hydrogen Energy, 2012
Perovskite-type LaCoO 3 oxide was prepared using Pechini's method and supported on alumina using a physical mixture and thermal treatment in order to obtain catalysts with different perovskite loadings (10, 20 and 40 wt.%). The catalysts were characterized by different methods and their catalytic potential was tested in the selective CO oxidation reaction (SELOX). Characterizations indicated that structural properties of LaCoO 3 did not change after supporting on the alumina and that the perovskite structure is resistant to reduction in the temperature range of SELOX reaction. The most active catalysts were the supported 40% LaCoO 3 /Al 2 O 3 and LaCoO 3 . The supported catalyst presented ca. twice as many metallic surface area than the unsupported sample, which suggests also twice as many perovskite at the surface and therefore higher activity. These results evidence that the supported perovskite oxides are very good alternative for SELOX reaction when compared to noble metal supported catalyst.
Co-doped LaAlO3 perovskite oxide for NOx-assisted soot oxidation
Applied Catalysis A: General, 2019
In the framework of nowadays challenges in the automotive catalysis, directed to the mitigation of pollution caused by the emissions of internal combustion engines, a series of LaAl1-xCoxO3 perovskites were investigated with the purpose of enhancing the oxidation of soot in the presence of NOx. Perovskite oxides LaAl1-xCoxO3 (x=0; 0.25; 0.5; 0.75 and 1) were synthesized by a solgel route and characterized by different methods: X-Ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), N2-sorption, O2/NOx-temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The perovskite oxides were tested as catalysts for NO oxidation in isothermal mode and for NOx-assisted soot oxidation in temperature programmed reaction. Structural results reveal that Co is well incorporated in the perovskite structure expanding the unit cell, and doping Co may result in the distortion of the BO6 octahedra of the general ABO3 perovskite structure. An increase in Co substitution with x up to 0.75 remarkably promotes the oxidation activity, whereas total replacement of Al by Co degrades the catalytic performance. Among the prepared solids, LaAl0.25Co0.75O3 is the most active for NO oxidation, with a conversion of 78% at 320 °C, and it also exhibits the highest activity for NOxassisted soot oxidation, with a T10% of 377 °C while maintaining high NO2 production (71%). The outstanding performance of LaAl0.25Co0.75O3 is associated with the high mobility of lattice oxygen species and the role of surface adsorbed oxygen seems not to be prominent. The strong correlation of catalytic activity with NOx-TPD profiles suggests that NOx adsorption on catalyst surface is an essential step in soot oxidation. It is also shown that higher calcination temperature promotes the crystallinity of perovskite phase and leads to the improvement in the catalytic activity. The present work indicates that the prepared perovskite catalysts are competitive with noble-metal rivals for NOx-assisted soot oxidation and outperform them in NO2 production for further NOx abatement.
Applied Catalysis B: Environmental, 2008
The nanometric Ln-Na-Cu-O (Ln = La, Pr, Nd, Sm, Gd) perovskite-like complex oxide catalysts were prepared by sol-gel auto-combustion method using citric acid as a ligand and an adjusting agent of particle-size and morphology. Their structures and physico-chemical properties were examined by chemical analysis, XRD, SEM, FT-IR, H 2 -TPR and MS-NO-TPD. The catalytic performances of these perovskite-like oxides for the simultaneous removal of soot and NO x were investigated by a technique of the temperature-programmed reaction (TPR). In the Ln-Na-Cu-O catalysts, the partial substitution of Na for La at A-site led to the formation of Cu 3+ and/or oxygen vacancy, thus the catalytic activity was remarkably enhanced. The optimal substitution amount of Na (x) is equal to 0.3 for the reduction of NO x , and x is equal to 0.7 for soot combustion. Moreover, attributing to the effects of very small surface particle sizes of the catalysts and the strong oxidizing ability of NO 2 which was produced from NO and O 2 in the reactant gases on these catalysts, the nanometric Ln-Na-Cu-O perovskite-like oxides exhibit very high catalytic activities for soot combustion even under loose contact conditions between soot and the catalyst. #