Ba-doped vs. Sr-doped LaCoO3 perovskites as base catalyst in diesel exhaust purification (original) (raw)
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Catalysis Today, 2018
Here we report the effects of strontium doping of perovskites (La 1-x Sr x CoO 3) on NO x storage and reduction (NSR) as well as the effects of supporting the perovskite onto an alumina support. The NSR capacity of La 0.7 Sr 0.3 CoO 3 improved with strontium doping: this material displayed a good balance between NO oxidation capacity and adsorption sites accessibility. Increased accessibility was mainly due to the strontium oxide segregates. In addition, different loadings of La 0.7 Sr 0.3 CoO 3 perovskite (10, 20, 30, 40 and 50%) were impregnated onto alumina in order to increase the exposed surface area of the perovskite. This had the effect of increasing the NSR capacity of the perovskite. The results of X-Ray diffraction, UV-vis-NIR spectroscopy, N 2 adsorption-desorption, electron microscopy, and temperature programmed techniques, demonstrated that the cobalt ions preferably formed cobalt aluminate (CoAl 2 O 4) in the case of low perovskite loadings (< 20%). Meanwhile, a well-developed perovskite phase was observed with the higher loadings (> 30%). The specific NO oxidation rate per gram of perovskite increased dramatically with the incorporation onto an alumina support. 30% LSCO/Al 2 O 3 sample had an oxidation rate of 138 μmol min-1 (g LSCO)-1 at 350°C, more than double the rate of the bulk La 0.7 Sr 0.3 CoO 3 (49 μmol min −1 (g LSCO) −1). Likewise, the 30% LSCO/Al 2 O 3 sample had a higher NO x storage capacity than its bulk counterpart at 400°C: 306 vs. 115 μmol (g LSCO) −1. The higher oxidation capacity of the alumina-supported samples also facilitated the diffusion of the intermediate compounds from oxidation to adsorption sites. Impregnating alumina with perovskite could be used to improve the efficiency of perovskite mediated NO x removal in automobile applications. Furthermore, adding palladium onto optimum alumina-supported perovskite sample, i.e. 1.5% Pd-30% LSCO/Al 2 O 3 , resulted in a clear improvement in NO x storage and reduction capacity. This last sample demonstrated a nitrogen yield as high as 65%, an improvement over the model Ptbased NSR catalyst.
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.
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.
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, 2017
Perovskites have attracted attention in recent years as an economic alternative to noble metals in oxidation processes. Synthesis conditions of LaCoO 3 and LaMnO 3 perovskites have been studied varying citrate to nitrate molar ratio in the starting solution, pH and calcination protocol, with the aim of obtaining high purity perovskites, absence of impurities, and with enhanced textural properties. Once synthesis conditions were established, strontium was incorporated in the perovskite lattice as a textural and structural promoter, by substituting lanthanum with different doping levels, i.e.
Journal of Thermal Analysis and Calorimetry, 2017
In this paper, catalytic reduction of NO by CO over perovskite-type oxides LaCu 0.7 B 0.3 O 3 (B = Mn, Fe, Co) synthesized by sol-gel method was investigated. LaCu 0.7 Mn 0.3 O 3 showed the highest activity among LaCu 0.7 B 0.3 O 3 perovskite catalysts (88% CO conversion and 93% NO conversion at 350°C). The effect of alkali and alkaline earth metals (Rb, Sr, Cs and Ba) on the structure and catalytic activity of LaCu 0.7 Mn 0.3 O 3 perovskite catalysts was also investigated. The results showed that catalytic activity was improved by partial substitution of La by alkali and alkaline earth metals. The superior activity of La 0.8 Sr 0.2 Cu 0.7 Mn 0.3 O 3 with respect to other catalysts (93% CO conversion and 96% NO conversion at 350°C) was associated with a higher reducibility at low temperature, more oxygen vacancies and synergistic effect between Cu and Mn. The catalysts were characterized by XRD, BET, H 2-TPR, XPS and SEM.
Perovskite-Based Catalysts as Efficient, Durable, and Economical NOx Storage and Reduction Systems
Catalysts, 2020
Diesel engines operate under net oxidizing environment favoring lower fuel consumption and CO2 emissions than stoichiometric gasoline engines. However, NOx reduction and soot removal is still a technological challenge under such oxygen-rich conditions. Currently, NOx storage and reduction (NSR), also known as lean NOx trap (LNT), selective catalytic reduction (SCR), and hybrid NSR–SCR technologies are considered the most efficient control after treatment systems to remove NOx emission in diesel engines. However, NSR formulation requires high platinum group metals (PGMs) loads to achieve high NOx removal efficiency. This requisite increases the cost and reduces the hydrothermal stability of the catalyst. Recently, perovskites-type oxides (ABO3) have gained special attention as an efficient, economical, and thermally more stable alternative to PGM-based formulations in heterogeneous catalysis. Herein, this paper overviews the potential of perovskite-based formulations to reduce NOx fr...
Applied Catalysis B: Environmental, 2020
Here we report the influence of surface composition on the NO x removal efficiency of lean NO x trap Pd-La 1x A x CoO 3 /Al 2 O 3-type catalysts. Three catalysts were prepared by the sequential impregnation of 30 wt.% of La 1x A x CoO 3-type perovskites and 1.9 wt.% of Pd over alumina. The following perovskite compositions were used: La 0.7 Sr 0.3 CoO 3 , La 0.7 Ba 0.3 CoO 3 or La 0.5 Ba 0.5 CoO 3. The results of X-Ray diffraction, N 2 adsorption-desorption at −196°C, electron microscopy, temperature programmed techniques, and Raman and X-ray photoelectron spectroscopies demonstrated that lanthanum partial substitution by barium promoted the presence of Ba-based phases homogeneously distributed at the surface. This fact together with the higher basicity of Ba than Sr led to an increase of the surface basicity for Ba-doped samples. Likewise, Ba doping also favors the formation of small PdO particles homogenously distributed over the surface in close contact with the perovskite phase. Hence, the interactions between Pd and surface basic sites were also promoted. As a result, 1.9 wt.% Pd-30 wt.% La 0.5 Ba 0.5 CoO 3 /Al 2 O 3 catalyst exhibited the highest NO x adsorption and reduction efficiency. Specifically, the NO global conversion and nitrogen production were as high as 90 % and 72 % at 350°C, respectively. The enhancement of NO x storage capacity during the lean period is mainly assigned to the displacement of gas/solid equilibrium between NO 2 and the available NO x adsorption sites due to the presence of higher concentration of basic sites at the surface. Meanwhile, the promotion of the NO x reduction capacity is due to the higher strength of NO x adsorbed species, which slows down the decomposition rate of NO x adsorbed species. Furthermore, the high proximity of Pd and perovskite phase favors the intermediate compounds diffusion. These results confirmed the excellent NO x removal efficiency of the 30 wt.% La 0.5 Ba 0.5 CoO 3-based catalyst, even above than Pt-based model catalyst.