LaMnO3 perovskite oxides prepared by different methods for catalytic oxidation of toluene (original) (raw)
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Korean Journal of Chemical Engineering, 2016
Catalytic oxidation of toluene over perovskite-type oxides of the general formula LaMn 1−x B x O 3 (B=Cu, Fe and x=0, 0.3, 0.7) and La 0.8 A 0.2 Mn 0.3 B 0.7 O 3 (A=Sr, Ce and B=Cu, Fe) was investigated, where the catalysts were synthesized by sol-gel auto combustion method. The catalysts were characterized by XRD, BET, H 2-TPR, XPS, and SEM. Obtained XRD patterns confirmed the perovskites to be single-phase perovskite-type oxides. Specific surface areas of perovskites were obtained between 25-40 m 2 /g. The perovskite catalysts showed high activity for the toluene oxidation. Based on the results, Fe-containing perovskite catalysts exhibited higher activity than Cu-containing perovskite catalysts. The substitution of Sr and Ce in A-site of the perovskite catalysts enhanced their activity for toluene oxidation. Among different synthesized catalysts in this research, La 0.8 Ce 0.2 Mn 0.3 Fe 0.7 O 3 has the highest activity. Nearly complete elimination of toluene was achieved at 200 o C with this catalyst. Based on Langmuir-Hinshelwood mechanisms, kinetic studies were conducted on toluene oxidation, indicating LH-OS-ND (adsorption of reagents on same types of sites and non-dissociative adsorption of oxygen) as the most probable mechanism which could predict the experimental data with correlation coefficient of R 2 =0.9952.
2017
In this paper, LaBO3 perovskite type catalyst formulations were prepared by sol-gel auto combustion method using citric acid as the fuel. Activity of catalysts was tested in catalytic oxidation of toluene as a model of volatile organic compounds. LaCoO3 perovskite formulation showed the highest activity among LaBO3 (Fe, Mn and Co) perovskite catalysts. So, LaCoO3 perovskite based catalyst was selected for further investigation and modification in order to improve catalytic activity. LaBO3 perovskite catalysts were modified by substitution of Co by Fe and Mn. The catalytic activity of LaCoO3 improved due to partial substitution of Co by Fe and Mn cations. LaCo0.7Mn0.3O3 showed the highest catalytic activity among the synthesized catalysts. The structures and morphology of synthesized perovskites were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. The results of X-ray diffraction indicated that the LaBO3 and LaCo0.7B′0.3O3 samples obtained usi...
Advances in Environmental Technology, 2019
In this study, La-Mn-Cr perovskite-type catalysts were synthesized as LaMnO3, LaCrO3, and LaMn0.5Cr0.5O3 by a microwave-assisted gel-combustion method. They were then calcined at 600 o C for 5h in air. X-ray diffraction (XRD) analysis indicated that the crystalline perovskite phase is the dominant phase formed in all the synthesized samples. The scanning electron microscopy (SEM) analysis showed that the perovskites have a full spongy and porous structure. The specific surface area (BET) analysis showed a specific surface area of about 12.4-26.8 m 2 /g, and the highest specific surface area belonged to the LaMn0.5Cr0.5O3 perovskite. Moreover, the highest oxygen mobility revealed by the temperature-programmed desorption of oxygen (O2-TPD) analysis was related to the LaMn0.5Cr0.5O3 sample. The catalytic activity of the synthesized perovskites in catalytic oxidation of 1000 ppm trichloroethylene (TCE) in air was investigated at different temperatures. The substituted perovskite (LaMn0.5Cr0.5O3) with the highest BET specific surface area and the highest oxygen mobility yielded the best catalytic performance among the probed perovskites.
Journal of Electroanalytical Chemistry, 2018
Lanthanum based electrocatalytically active LaMO 3 (M=Cr, Mn, Fe, Co, Ni) perovskites were synthesized using a single step solution combustion technique. The structural and morphological properties of the catalysts were studied using XRD, SEM, and TEM. The synthesis conditions are found to have a siginificant effect on the nature of the nanoparticles and it can be tuned to synthesize amorphous or crystalline materials. The perovskites showed exceptional performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in alkaline medium. LaMnO 3 is found to be most active for ORR, whereas LaCoO 3 for OER. The onset potential of LaMnO 3 is-0.12 V, and for other La-transition metals is nearly-0.2 V. The Koutechy-Levich
La1−xCaxMnO3 perovskites as catalysts for total oxidation of volatile organic compounds
Catalysis Today, 2011
La 1−x Ca x MnO 3 perovskites were prepared by the citrate method and characterized by means of X-ray diffraction, temperature programmed desorption of oxygen, temperature programmed reduction, and measurement of specific surface area. The characterization results indicated that pure perovskite phases were obtained and their specific surface areas are appropriate for the application in catalytic oxidation. The unsubstituted perovskite, LaMnO 3 , could present a certain amount of Mn 4+ and cationic vacancies, which is generally called oxidative nonstoichiometry. The electronic unbalance yield by the partial substitution of lanthanum by calcium, a cation of lower oxidation state, caused an oxidation state increase of part of the manganese occupying the B sites of the structure. Concurrently, the amount of cationic vacancies decreased with the increase of calcium amount. The catalytic activity was evaluated in the combustion of ethanol and n-hexane. Both reactions would occur by means of a suprafacial reaction mechanism in which the adsorbed oxygen species are relevant.
Applied Catalysis B: Environmental, 2008
Two new series of perovskite-type oxides LaMO 3 (M = Mg, Ti, Fe) with different ratio Mg/Fe (MF) and Ti/Fe (TF) in the B cation site were prepared by annealing the precursor, obtained by the mechanochemical activation (MCA) of constituent metal oxides, at 1000 8C in air. In addition, two closely related perovskites LaFeO 3 (LF) and LaTi 0.5 Mg 0.5 O 3 (TM (50:50)) were synthesized in the similar way. Using MCA method, perovskites were obtained in rather short time and at room temperature. The samples were characterized by X-ray powder diffraction (XRPD), Xray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), temperature programmed desorption of oxygen (TPD), Mössbauer spectroscopy, BET surface area measurements and tested in methane deep oxidation. According to XRPD analysis all synthesized samples are almost single perovskite phase, with trace amounts of La 2 O 3 phase. Data of Mössbauer spectroscopy identify Fe 3+ in octahedral coordination. The activity of perovskite in methane deep oxidation increases in the order TM (50:50) < MF series < TF series. Higher activity of TF samples in respect to MF with similar Fe content can be related to the structural characteristic, mainly to the presence of predominantly most labile oxygen species evidenced by TPD at lowest temperature of oxygen evaluation. In used experimental conditions, the Fe substituted perovskite are thermal stable up to the temperature of 850 8C. The stability of Fe active sites is probably the most important parameter responsible for thermal stability of perovskite, but the atomic surface composition also should be taken into account. #
Study of Oxygen Reactivity in La1−x Sr x CoO3−δ Perovskites for Total Oxidation of Toluene
Catalysis Letters, 2012
The total oxidation of toluene is studied over catalytic systems based on perovskite with general formula AA 0 CoO 3-d (A = La, A 0 = Sr). The systematic and progressive substitution of La 3? by Sr 2? cations in the series (La 1-x Sr x CoO 3-d system) of the perovskites have been studied to determine their influence in the final properties of these mixed oxides and their corresponding reactivity performance for the total oxidation of toluene as a model volatile organic compound with detrimental effects for health and environment. The structure and morphology of the samples before and after reaction have been characterized by XRD, BET and FE-SEM techniques. Additional experiments of temperature programmed desorption of O 2 in vacuum and reduction in H 2 were also performed to identify the main surface oxygen species and the reducibility of the different perovskites. It is remarkable that the La 1-x Sr x CoO 3-d series presents better catalytic performance for the oxidation of toluene, with lower values for the T 50 (temperature of 50 % toluene conversion) than the previously studied LaNi 1-y Co y O 3 series.
Materials Chemistry and Physics, 2003
Three kinds of Mn-containing perovskites, LaMnO3, La0.9MnO3 and LaMn0.9O3, have been investigated for methane combustion in the temperature range 475–600°C. It has been possible to evidence that LaMn0.9O3 shows the greatest catalytic activity, probably because of its surface area, and also because its defect structure is favourable for development of active sites. The conversion observed as a function of temperature
Catalytic Oxidation of CO Over LaMn1−xBxO3 (B = Cu, Fe) Perovskite-type Oxides
Catalysis Letters, 2016
In this paper, catalytic oxidation of CO over perovskite-type oxides LaMn 1-x B x O 3 (B = Cu, Fe and x = 0, 0.1, 0.3, 0.5) were investigated. The perovskite catalysts were synthesized by sol-gel method and characterized by XRD, BET, H 2-TPR, XPS and SEM. XRD patterns showed that the samples are single-phase perovskite. By introduction of Cu and Fe in the structure, Specific surface area of LaMnO 3 was decreased, but the reducibility and oxygen vacancy were increased. The synthesized perovskite catalysts show high activity for the CO oxidation. Substitution of Mn by Cu and Fe enhanced the catalytic activity. The cu-containing perovskites showed a higher activity in CO oxidation compared with Fe-containing perovskites. The LaMn 0.7 Cu 0.3 O 3 perovskite showed the highest activity among the synthesized perovskites (T50 and T90 % of 110 and 142°C). The excellent activity of LaMn 0.7 B 0.3 O 3 was associated to reducibility at low temperature, more oxygen vacancies and synergistic effect between Cu and Mn. The apparent activation energies were obtained and LaMn 0.7 Cu 0.3 O 3 as the most active catalyst, has the least activation energy compared with other synthesized catalysts.
Three-Way Catalytic Activity and Oxygen Storage Capacity of Perovskite LaMn0.976Rh0.024O3+δ
Journal of Catalysis, 1997
A La(MnRh)O 3.15 catalyst, containing 1 wt% Rh, was prepared by a citrates/polyacrylamide gel method, leading to a sample with a specific surface area of 27 m 2 /g after calcination at 700 • C. This catalyst shows high activity in three-way catalysis reactions for the simultaneous reduction of NO and oxidation of CO and C 3 H 6 . However, the addition of 10 vol.% steam slightly deactivates the catalyst, mainly for NO reduction. Large amplitude oscillations of the feed streams between oxidizing and reducing compositions do not deactivate the sample: these variations in the composition are compensated for by the high mobility of the over-stoichiometric oxygen, which is available to oxidize CO under a reducing feed stream and is easily replenished by O 2 or NO in the presence of an oxidizing feed stream. This mobility corresponds to the reversible structural change, at low temperature, between hexagonal La(MnRh)O 3.15 and orthorhombic La(MnRh) 3.00 , leading to an oxygen storage capacity of 0.15 mole [O] per mole of catalyst.