Bulk LaMnO3 Research Articles

Supercritical CO2-Guided Passivation Strategies for Oxygen Vacancy Modulation in LaMnO3.

The development of 2D magnetic materials and the modulation of intrinsic magnetism are essential for the exploration of new materials in the field of information storage. Despite its strong ferromagnetic properties, LaMnO3 is hindered by a high number of oxygen defects, which result in a relatively short lifetime when employed in electronic memory devices. Here the successful transformation of bulk LaMnO3 into a 2D structure using supercritical carbon dioxide.is reported. This technique enables the successful modulation of the magnetic properties of the material. Interestingly, it is found that the oxygen defect is repaired, which is in sharp contrast to conventional perovskites. These promising results demonstrate the potential of using the magnetic properties of LaMnO3, which is of great importance in the context of expanding its application in electronic devices.

Emergent half-metal with mixed structural order in (111)-oriented (LaMnO3)2n|(SrMnO3)n superlattices

Using first-principles techniques, we study the structural, magnetic, and electronic properties of (111)-oriented (LaMnO3)2n|(SrMnO3)n superlattices of varying thickness (n=2,4,6). We find that the properties of the thinnest superlattice (n=2) are similar to the celebrated half-metallic ferromagnetic alloy La2/3Sr1/3MnO3, with quenched Jahn-Teller distortions. At intermediate thickness (n=4), the a−a−a− tilting pattern transitions to the a−a−c+ tilting pattern, driven by the lattice degrees of freedom in the LaMnO3 region. The emergence of the Jahn-Teller modes and the spatial extent needed for their development play a key role in this structural transition. For the largest thickness considered (n=6), we unveil an emergent separation of Jahn-Teller and volume-breathing orders in the ground-state structure with the a−a−c+ tilting pattern, whereas it vanishes in the antiferromagnetic configurations. The ground state of all superlattices is half-metallic ferromagnetic, not affected by the underlying series of structural transitions. Overall, these results outline a thickness-induced crossover between the physical properties of bulk La2/3Sr1/3MnO3 and bulk LaMnO3. Published by the American Physical Society 2024

Raman spectroscopy of the Jahn–Teller phonons in a magnetic LaMnO3 thin film grown on KTaO3

Bulk LaMnO3 is an A-type antiferromagnetic material in which the Jahn–Teller (JT) planes each have a ferromagnetic arrangement, but are stacked in antiparallel. Here, we report the growth of epitaxial LaMnO3 films on (001)-oriented cubic KTaO3 substrates in such a way that the JT plane is parallel to the nonmagnetic substrate. We verify the presence of the JT distortion and confirm the orientation of the plane by symmetry analysis with angle-resolved polarized Raman spectroscopy. The temperature evolution of the Raman spectra indicates that the B1g JT phonon softens below the magnetic transition temperature of ∼145 K, where ferro- or ferri-magnetism with magnetic easy axis along the out-of-plane direction is exhibited.

In situ fabrication of robust three dimensional ordered macroporous γ-MnO2/LaMnO3.15 catalyst for chlorobenzene efficient destruction

Catalytic activity of perovskite oxides as LaMnO3+δ is greatly limited by their low surface area and deficient active site density though they are thought to be one category of desired candidates for noble metal-based catalysts. Here, a robust three dimensional ordered macroporous (3DOM) γ-MnO2/LaMnO3.15 (Mn/3DLM) was in situ fabricated by the strategy of selectively dealloyed surface La cations. Mn/3DLM displayed excellent activity with 90% of chlorobenzene destructed at 207 °C (apparent activation energy of 45.4 kJ/mol), obviously lower than those of γ-MnO2 (244 °C; 51.9 kJ/mol) and bulk LaMnO3.15 (311 °C; 70.2 kJ/mol) owing to large surface area, excellent reducibility, and improved surface active oxygen concentration. Nucleophilic substitution was the main process for active oxygen attacking, while electrophilic substitution mainly contributed to chlorinated byproducts formation. Remarkably, reaction byproducts as phenol, o-dichlorobenzene, trichloroethylene, and bichloroethylene over Mn/3DLM can be efficiently inhibited during the long-term operations via weakened the electrophilic substitution effect.

Casein templated synthesis of porous perovskite and its application in visible-light photocatalytic degradation of methylene blue

Porous LaMnO3 perovskite was successfully fabricated by biotemplate method utilizing casein as template to control the morphology. The impact of casein template on the phase structure, microstructure and morphologies of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray Energy dispersive spectrometer (EDS). The photocatalytic degradation test of methylene blue revealed that the biotemplated porous LaMnO3 showed superior performance in comparison to the bulk LaMnO3 particles, which was probably due to its small crystallite size, porous structure, large surface area and narrow band gap.

Enhanced low-temperature activity of LaMnO3 for toluene oxidation: The effect of treatment with an acidic KMnO4

In this work, MnO2/LaMnO3 catalysts derived from LaMnO3 perovskite were prepared in situ via a facile selective removal and oxidation method using acidic KMnO4 solution. For bulk LaMnO3 perovskite, the A-site cations (La) were dissolved and B-site cations (Mn3+) were simultaneously oxidized to Mn4+ with acid treatment. The modified catalyst exhibited better activity for toluene oxidation than bulk LaMnO3. This method improves the Mn4+ content on the LaMnO3 surface with good low temperature reducibility. Meanwhile, this method increases the specific surface area and provides more oxygen vacancies on the surface. These results are beneficial for the toluene adsorption and its ring-opening reaction. Moreover, MnO2/LaMnO3 still maintained good thermal stability for toluene oxidation at high temperatures resulting from the presence of the perovskite structure.

Strain-induced insulating ferromagnetism in LaMnO3 thin films from first-principles investigations

Previous experiments have found that LaMnO3 thin films grown on SrTiO3 substrate exhibit insulating ferromagnetism different from that of the bulk LaMnO3. Utilizing first-principles calculations based on density functional theory, magnetic transitions, energy gaps and spin exchange interactions of LaMnO3 thin films with different epitaxial strains are investigated, and the effect of the Jahn-Teller distortion, rotation and tilt of oxygen octahedrons on magnetic and electrical properties are analyzed in detail. A relative narrow insulating ferromagnetic area without structural phase transition is obtained during the transition from metallic ferromagnetic phase to insulating A-type antiferromagnetic phase. If the magnetic transition of LaMnO3 film is attributed to Jahn-Teller distortion, then the metal–insulator transition should be ascribed to the tilt of the oxygen octahedron and large change of the O1-Mn-O2 angle in ab plane, which is helpful to understand the insulating ferromagnetic characters during the preparations of the LaMnO3 superlattices or heterostructures, also indicates that the insulating ferromagnetic properties of LaMnO3 films can be tuned by epitaxial strain-controlled oxygen octahedrons distortions.

Density Functional Theory Modeling of Cation Diffusion in Bulk Lanthanum Manganite and Tetragonal Zirconia for Solid Oxide Fuel Cell Applications

Cation diffusion in perovskites such as La1-xSrxMnO3±δ (LSM) and fluorites such as Yttria Stabilized Zirconia (YSZ) plays a key role in controlling performance and long-term stability of solid oxide fuel cells (SOFCs) and of the corresponding electrode/electrolyte interfaces. For point defects based cation migration mechanisms, discrepancies between experimental studies and atomistic modeling results are generally observed when trying to identify the apparent activation energies of the cation diffusivities. In particular, computational modeling of the simple point defect migration generally overestimates the apparent activation energies by several eVs [1-3] relative to experimental results. Despite the existence of few proposed defect cluster pathways in the SOFC literature, the corresponding energetics based on atomistic level modeling is quite limited. As a result, outstanding questions related to the influence of the local bonding environment of the material upon the activation energies of cation diffusion and upon the energetics of the defect cluster carriers are still open. In this presentation, density functional theory (DFT) calculations of the cation diffusion involving mechanisms beyond the isolated point defect migration mechanism are discussed in connection to SOFC applications. The barriers of the cations, cation vacancy clusters, and cation impurities migration as well as their corresponding saddle point configurations in bulk LaMnO3±δ (LMO) and tetragonal ZrO2 are investigated. For cation vacancy migration in both LaMnO3 and tetragonal ZrO2 systems, it was revealed that significant reduction in the barriers of 1~3 eV takes place when there exists an additional nearest neighbor vacancy or a nearest neighbor vacancy pair bound to the original cation vacancy transport carrier (i.e., partially or fully bound Schottky defects). Such a significant reduction in the migration barriers of isolated cation vacancy migration due to the presence of an additional nearest neighbor vacancy or a vacancy pair invokes the need to examine other possible defect cluster diffusion mechanisms that exhibit attractive or weakly repulsive interactions between point defects. For example, our recent studies [1,3] suggest that the presence of a nearest neighbor B-site cation vacancy in bulk LMO decreases the electrostatic repulsion and steric constraints to the migrating A-site cations in the transition state configurations, leading to a more active A-site cation diffusion with apparent activation energies in good agreement with the experimental measurements. An analogous scenario is also observed for the Lanthanide impurity migration (via a cation vacancy related mechanism) in tetragonal ZrO2, where the migration barriers of partial and full Schottky bound defects are about 1.5 and 2.4 eV lower than those of simple cation vacancy migration (about 3 eV). By considering the attractive interactions of -1.0 and -1.4 eV for the partial (VZr-VO) and full (VO-VZr-VO) bound Schottky defects along with the separated Schottky defect formation energies of 4~5 eV (in a 288-atom ZrO2 supercells), it follows that cation impurity diffusion via partially and fully bonded Schottky defects could be more active than the cation vacancy migration of the separated Schottky defects in tetragonal ZrO2. Finally, the trends in the migration barriers of the defect cluster mechanisms among several types of cation impurities relevant for SOFC applications in LMO and tetragonal ZrO2 will be also discussed.

Evolution of structure and magnetic properties of stoichiometry and oxygen rich LaMnO3 nanoparticles

In this report, the evolution of structure and magnetic properties in stoichiometry and oxygen rich LaMnO3 samples synthesized by a simple, cost effective, conventional co-precipitation technique are systematically studied. While X-ray powder diffraction reveals a monoclinic, I2/a structure in both samples, Reitveld refinement demonstrates higher John-Teller (J-T) distortion in the former one. Higher J-T distortion is accompanied with a large deviation in MnO bond length. FESEM (Field Emission Scanning Electron Microscopy) analysis combined with crystallite size calculated from XRD peak profile suggest that the particles are of 50–60nm and are polycrystalline in nature. The antiferromagnetism observed in bulk LaMnO3 with TN=140K evolves towards a ferromagnetic order in both stoichiometry and oxygen rich samples. However, Curie temperature, TC, is found to be higher in oxygen rich sample due to higher MnOMn bond angle. The large effective magnetic moment calculated from Curie-Weiss plot is found to be higher in stoichiometry sample. Higher moment is ascribed to high oxygen vacancies evidenced from XPS analysis. Dispersion behavior observed in frequency dependent ac susceptibility (χ) indicates the spin-glass, cluster-glass and interacting superparamagnetic behavior. Fitting the susceptibility data with phenomenological models such as Neel-Arrhenius, Vogel-Fulcher and Power law, while canonical spin-glass, cluster-glass and interacting superparamagnetism is ruled out, the spin-glass behavior with a higher relaxation time in oxygen rich sample is confirmed.

Density Functional Theory Modeling of A-site Cation Diffusion in Bulk LaMnO3 ±δ for Solid Oxide Fuel Cell Cathodes

In this work, the diffusion barriers of A-site cation and dopants in bulk LaMnO3±δ (LMO) are determined based on density functional theory (DFT) simulations. These properties are highly relevant for solid oxide fuel cell (SOFC) cathode applications. Due to the weak repulsive interactions (0.2~0.3 eV) between the nearest neighbor A-site and B-site cation vacancies, the A-site and B-site cation vacancy clusters can readily form in LMO. The DFT modeling unveils a facile A-site cation diffusion pathway via a cation vacancy cluster mechanism with a migration barrier reduction of about 1.3 eV versus the direct A-site vacancy migration. By combining these results with the bulk LMO defect modeling, the temperature and oxygen partial pressure dependences of the A-site cation tracer diffusion coefficients are assessed based on the concentration of transport carriers and the migration barriers associated with the A-site cation transport in bulk LMO. The trends in the migration barriers vs. various types of metal cations relevant to SOFC applications i.e. La3+, Sr2+, Zr4+, Y3+, are also investigated, and the results obtained suggest that both the ionic charge and the ionic radius correlate with the calculated cation migration barriers

Modelling oxygen defects in orthorhombic LaMnO3 and its low index surfaces.

LaMnO3-based perovskites, which have been extensively studied as cathodes for high temperature solid oxide fuel cells (SOFCs), are also of interest for intermediate temperature SOFCs (T = 600-1000 K). Oxygen vacancy formation is required in LaMnO3 for oxygen diffusion, therefore a low vacancy formation energy is preferable. The stability of the low index surfaces of orthorhombic LaMnO3 has been investigated, with the {010} surface found to be the most stable. Surface stability was found to be affected by the La and Mn coordination, and the Mn-O bonds cleaved on surface formation. The crystal morphology has been predicted, in order to determine the most likely terminations to be present. The formation of oxygen vacancies in bulk LaMnO3 and at all of its low index surfaces has been examined, and it has been found that formation of vacancies in the bulk has a high energy, while there is a large variation in formation energies at the low index surfaces, which is likely to lead to segregation of vacancies to the surface of orthorhombic LaMnO3.

Fabrication of LaMnO3+ δ Oxygen Reduction Reaction Catalyst using Laser Ablation Synthesis in Solution Method

The catalysts play an important role in energy devices including fuel cell and Li-air batteries. Usually, platinum (Pt) and platinum alloy (Pt alloy) are used in these devices, due to their good catalytic performance such as high oxygen reduction reaction (ORR) activity and high onset potential. However, Pt is very expensive in comparison with the other metal and non-metal catalysts, which limits commercialization of energy technologies. Cost-effective perovskite structure transition-metal oxide catalysts have shown reasonably high activity for the ORR as well as high electronic and ionic conductivity.[1] Especially, LaMnO3+δ exhibits the highest ORR activity value among perovskite catalysts because it satisfies the Sabatier’s principle as possessing approximately 1 electron in e g band of d orbital.[2] In the catalytic reaction, nanometer-sized (<10 nm) particles possess a large surface area which leads to a high catalytic efficiency; however, it is hard to achieve nanometer-sized particles from typical chemical reaction synthesis. Laser ablation synthesis in solution (LASiS), which is a simple, fast, and clean process, is suitable to achieve nanometer-sized pure LaMnO3+δ particles by controlling laser parameters. In this study, we fabricated the LaMnO3+δ catalyst powder which has large surface area for improving catalytic efficiency using LASiS. Also, we compared the ORR efficiency among synthesized LaMnO3+δ/GCB powder, LaMnO3+δ bulk, and Pt/C through a rotation disk electrode (RDE) method. The LaMnO3+δ target for LASiS was prepared using solid state reaction with La2O3 and MnO2 powder. The powder was put in zirconia jar with isopropyl alcohol (IPA) and zirconia ball, and then mixed using planetary ball mill for 120 minutes. Mixed powder was dried at 100°C in oven and then calcined at 900°C for 12 hours under air atmosphere in furnace. A disk- pellet was made using cold isostatic pressure (CIP) method. The pellets were sintered at 1200°C for 24 hours under the air atmosphere. The target soaked in ethanol was ablated to a Q-switched Nd:YAG pulsed laser source providing a 8-ns pulse width with wavelength of 266 nm with repetition rate of 10 Hz. The laser energy and spot size were around 65 mJ/pulse and 1.5 mm respectively, which corresponded to a laser energy density of 3.67 J/cm2. Colloidal solution from LASiS was mixed with 6M HCl treated GCB before drying at 80°C in oven and then obtained powder were annealed at 500°C to 800°C for 30 minutes under the air atmosphere in furnace. We found that the synthesized LaMnO3+δ/GCB powder annealed at 800°C for 30 minutes shows the highest ORR activity. Its half wave potential value was around 0.83 V versus reversible hydrogen electrode (vs. RHE), corresponding to around 150 mV higher than bulk LaMnO3+δ. Also, the conventional Tafel plot results indicate that the ORR efficiency of LaMnO3+δ/GCB catalyst is similar to that of Pt/C 20 wt%. Specific activity at 0.8 V vs. RHE was improved by more than 15 times in comparison to bulk LaMnO3+δ. [1] D. Chen et al., Chem. Rev. 115, 9869 (2015). [2] J. Suntivich et al., Nature Chemistry. 3, 546 (2011).

First-principles study of the electronic properties and magnetism of LaMnO3/SrTiO3 heterointerface with the different component thickness ratios

Using first-principles calculations based on density functional theory and projector augmented wave method, we investigate the thickness ratio dependences of the ionic relaxation, electronic structure, and magnetism of (LaMnO3)n/(SrTiO3)m heterostructure. Polar and nonpolar oxide interfaces have become a hot point of research in condensed matter physics; in this system, polar discontinuity at the interface may cause charge transfer to occur at interfaces between Mott and band insulating perovskites. Here, we consider two types of interfaces, namely n-type (LaO)+/(TiO2)0 and p-type (MnO2)-/(SrO)0 interfaces. The results show that the different thickness ratios and interface-types lead to different degrees of ionic relaxation, inducing charges of different concentrations to transfer. The distortions of the oxygen octahedra are found to vary distinctly with the component thickness ratio (n:m), which is consistent with recent experimental results. Furthermore, both n and m are found to strongly affect the charge transfer. When the thickness of LaMnO3 reaches a thickness of critical layers of 6 unit cells, the Mn-eg electrons are transferred to the Ti-dxy orbitals of SrTiO3, which is caused by the interface polar discontinuity. Two-dimensional electron gas with high mobility is formed in an n-type (LaMnO3)n/(SrTiO3)2 interface region. Meanwhile, spin polarization of interface-layer Ti atoms becomes more obvious, which induces Ti magnetic moment to be close to 0.05B. We find that Mn magnetic moment of 3.9B is a larger value at the n-type interface than at the p-type interface. The above studied heterostructure favours ferromagnetic spin ordering rather than the A-type antiferromagnetic spin ordering of bulk LaMnO3. Whether n-type or p-type (LaMnO3)2/(SrTiO3)8 interfaces consist of ultrathin LaMnO3 layer and thicker SrTiO3 layer, there is no structure distortion at the side of SrTiO3 basically, which is in agreement with experimental results. Stronger interface-layer polar distortions for p-type interface prevent the electron transfer from occurring, and spin polarization of Ti cannot occur either. In addition, it is found that the two types of interfaces possess 2 eV potential difference by comparing the average electrostatic potential, thus charge transfer is more difficult to occur in the p-type interface than in the n-type interface.

Trends in (LaMnO3)n/(SrTiO3)m superlattices with varying layer thicknesses.

We investigate the thickness dependence of the structural, electronic, and magnetic properties of (LaMnO3)n/(SrTiO3)m (n, m = 2, 4, 6, 8) superlattices using density functional theory. The electronic structure turns out to be highly sensitive to the onsite Coulomb interaction. In contrast to bulk SrTiO3, strongly distorted O octahedra are observed in the SrTiO3 layers with a systematic off centering of the Ti atoms. The systems favour ferromagnetic spin ordering rather than the antiferromagnetic spin ordering of bulk LaMnO3 and all show half-metallicity, while a systematic reduction of the minority spin band gaps as a function of the LaMnO3 and SrTiO3 layer thicknesses originates from modifications of the Ti dxy states.

Surface Energetics of Nanoscale LaMnO3+δ Perovskite

Perovskite type LaMnO3 and related materials are important compounds with many useful and unique physical and chemical properties. There is a lack of experimental thermochemical data on the energetics of LaMnO3 nanoparticles. In this work, a series of LaMnO3+δ samples were synthesized via the citrate method and calcined at 700°C–1050°C. All samples displayed rhombohedral structure (X‐ray diffraction) with similar oxygen stoichiometry 3+δ = 3.16–3.18 (iodometric titration coupled with gravimetric analysis). The BET surface area varied from null for bulk sample to 6.88 ± 0.08 × 103 m2/mol for the sample calcined at 700°C. The water content varied linearly with the surface area with the highest value being 2.34 wt%. The chemisorbed water adsorption enthalpy was −63.0 ± 4.1 kJ/mol with the chemisorbed water coverage of 8 H2O/nm2. High‐temperature oxide melt drop solution calorimetry, performed in sodium molybdate at 702°C, yielded enthalpy of formation from La2O3, Mn2O3, and O2 of bulk LaMnO3.16 of −77.85 ± 1.94 kJ/mol. After correction of drop solution enthalpies of nanometric samples for water content, the calorimetric data were used to calculate the surface energy of LaMnO3+δ. The energy of the anhydrous surface was 2.27 ± 0.29 J/m2, and that of the hydrous surface was 2.02 ± 0.27 J/m2. These values are higher than the surface energies of LaMnO3.00 predicted elsewhere by theoretical methods, probably due to the different oxygen content and possibly more complex surface structure and exposed surface planes. The measured surface energy of LaMnO3+δ lies between the values reported recently for BaTiO3 and PbTiO3 and close to the reported values for MnO2. This suggests that LaMnO3+δ surface is predominantly MnO2‐terminated, in line with the trends predicted by theoretical calculations.

PMMA-templating generation and high catalytic performance of chain-like ordered macroporous LaMnO3 supported gold nanocatalysts for the oxidation of carbon monoxide and toluene

Rhombohedrally crystallized chain-like LaMnO3 and its supported gold (xAu/LaMnO3; x=1.4, 3.1, and 4.9wt%) catalysts have been prepared using the poly(ethylene glycol)-assisted polymethyl methacrylate-templating and gas bubble-assisted polyvinyl alcohol-protected reduction methods, respectively. It is shown that there were good correlations of surface adsorbed oxygen species concentration and low-temperature reducibility with catalytic activity of the samples for the oxidation of CO and toluene. Among the LaMnO3 and xAu/LaMnO3 samples, 4.9Au/LaMnO3 performed the best, giving the T50% and T90% of 61 and 91°C for CO oxidation, and of 201 and 226°C for toluene combustion, respectively. The apparent activation energies (29–50 and 47–62kJ/mol) of the chain-like LaMnO3 and xAu/LaMnO3 samples were much smaller than those (63 and 97kJ/mol) of the bulk LaMnO3 sample for the oxidation of CO and toluene, respectively. We believe that the higher surface area and oxygen adspecies concentration and better low-temperature reducibility as well as the strong interaction between Au nanoparticles and chain-like LaMnO3 support might account for the high catalytic performance of 4.9Au/LaMnO3.

High mobility half-metallicity in the (LaMnO3)2/(SrTiO3)8 superlattice

First principles calculations have been performed to investigate the LaMnO3/SrTiO3 superlattice. Structural relaxation within the generalized gradient approximation results in no significant tiltings or rotations of oxygen octahedra, but in distinct distortions in the SrTiO3 region. Taking into account the onsite Coulomb interaction, we find that the Mn spins order ferromagnetically, in contrast to the antiferromagnetic state of bulk LaMnO3. Most importantly, the interface strain combined with charge transfer across the interface induces half-metallicity within the MnO2 layers. The superlattice is particulary interesting for spintronics applications because the half-metallic states are characterized by an extraordinary high mobility.

Magnetocaloric properties of nanocrystalline LaMnO3: Enhancement of refrigerant capacity and relative cooling power

We report the significantly improved magnetocaloric properties of sol–gel prepared nanocrystalline samples of LaMnO3 with average particle size ∼200nm and ∼40nm in comparison with their bulk counterpart. The samples show negligible hysteresis losses in the ferromagnetic state and exhibit large magnetocaloric effect associated with their paramagnetic to ferromagnetic (PM–FM) transition. In comparison with bulk LaMnO3, both refrigerant capacity (RC) and relative cooling power (RCP) are greatly enhanced (up to 65%) in the nanocrystalline samples. This is attributed to the presence of superparamagnetic (SPM) nanoclusters near and above the PM–FM transition for the nanoparticles. For a field change of 5T, the sample with average particle size ∼40nm shows RCP as large as ∼369J/kg, which is about 2.6 times larger than that reported for Gd nanoparticles (mean size ∼15nm) and even comparable to that of bulk Gd (∼410J/kg). Our studies reveal that the reduction of particle size to the nanoscale can be an effective way of increasing RC and RCP of manganite materials.

Lysine-aided PMMA-templating preparation and high performance of three-dimensionally ordered macroporous LaMnO3 with mesoporous walls for the catalytic combustion of toluene

Rhombohedrally crystallized three-dimensionally ordered macroporous (3DOM) perovskite-type oxides LaMnO3 with mesoporous skeletons were prepared using the poly(ethylene glycol) (PEG)- and/or l-lysine-assisted poly(methyl methacrylate) (PMMA)-templating method. Physicochemical properties of the materials were characterized by numerous analytical techniques. Catalytic performance of the as-prepared LaMnO3 samples was evaluated for the combustion of toluene. It is found that addition of appropriate amounts of PEG400 and l-lysine was beneficial for the generation of high-quality 3DOM-structured LaMnO3 (denoted as LaMnO3-PL-1, LaMnO3-PL-2, and LaMnO3-PL-3 derived with a PEG400/l-lysine molar ratio of 1.23, 0.61, and 0.31, respectively) with mesoporous skeletons and high surface areas (32–38m2/g). Among the LaMnO3 samples, the LaMnO3-PL-2 one possessed the largest surface area and the highest contents of surface Mn4+ and adsorbed oxygen species. 3DOM-structured LaMnO3 showed better low-temperature reducibility than bulk LaMnO3, with the LaMnO3-PL-2 sample displaying the best low-temperature reducibility. Under the conditions of toluene concentration=1000ppm, toluene/O2 molar ratio=1/400, and space velocity=20,000mL/(gh), the porous LaMnO3 catalysts remarkably outperformed the nonporous bulk counterpart; over the best-performing LaMnO3-PL-2 catalyst, the temperatures required for toluene conversion=50 and 90% were ca. 226 and 249°C, respectively. The apparent activation energies (58–61kJ/mol) for toluene combustion over the LaMnO3-PL-1–3 catalysts were much lower than that (97kJ/mol) over the bulk LaMnO3 catalyst. It is concluded that the large surface area, high oxygen adspecies content, good low-temperature reducibility, and unique bimodal pore structure were responsible for the good performance of 3DOM-architectured LaMnO3 with mesoporous skeletons for toluene combustion.

Controlled preparation and high catalytic performance of three-dimensionally ordered macroporous LaMnO3 with nanovoid skeletons for the combustion of toluene

Three-dimensionally ordered macroporous (3DOM) single-phase rhombohedral perovskite-type oxide LaMnO3 materials with nanovoid skeletons were prepared using the poly(methyl methacrylate)-templating methods with the assistance of surfactant (poly(ethylene glycol) (PEG) or triblock copolymer (Pluronic P123)). The nature of surfactant influenced the pore structure of the LaMnO3 sample. The use of PEG400 alone led to a 3DOM-structured LaMnO3 without nanovoid skeletons; with the addition of PEG400 and P123, however, one could prepare LaMnO3 samples with high-quality 3DOM structures, nanovoid skeletons, and high surface areas (37–39m2/g). Under the conditions of toluene concentration=1000ppm, toluene/O2 molar ratio=1:400, and space velocity=20,000mL/(gh), the porous LaMnO3 samples were superior to the bulk counterpart in catalytic performance, with the nanovoid-containing 3DOM-structured LaMnO3 catalyst performing the best (the temperatures for toluene conversions of 50% and 90% were 222–232 and 243–253°C, respectively). The apparent activation energies (57–62kJ/mol) over the 3DOM-structured LaMnO3 catalysts were much lower than that (97kJ/mol) over the bulk LaMnO3 catalyst. We believe that the excellent performance of the 3D macroporous LaMnO3 materials in catalyzing the combustion of toluene might be due to factors such as large surface area, high oxygen adspecies concentration, good low-temperature reducibility, and unique nanovoid-containing 3DOM structure of the materials.