CO and soot oxidation over macroporous perovskite LaFeO3

Exploring Reversible Redox Behavior in the 6H-BaFeO3-δ (0 < δ < 0.4) System: Impact of Fe3+/Fe4+ Ratio on CO Oxidation

This work is devoted to evaluating the relationship between the oxygen content and catalytic activity in the CO oxidation process of the 6H-type BaFeO3-δ system. Strong evidence is provided about the improvement of catalytic performance with increasing Fe average oxidation state, thus suggesting the involvement of lattice oxygen in the catalytic process. The compositional and structural changes taking place in both the anionic and cationic sublattices of the catalysts during redox cycles have been determined by temperature-resolved neutron diffraction. The obtained results evidence a structural transition from hexagonal (P63/mmc) to orthorhombic (Cmcm) symmetry. This transition is linked to octahedra distortion when the Fe3+ concentration exceeds 40% (δ values higher than 0.2). The topotactical character of the redox process is maintained in the δ range 0 < δ < 0.4. This suggests that the cationic framework is only subjected to slight structural modifications during the oxygen exchange process occurring during the catalytic cycle.

Insights into the interface of NiCo2O4 spinel /LaCoO3 perovskite nano-composite for CO and soot oxidation

In the quest for the development of thermally stable, highly active and low-cost catalysts for use in catalyzed diesel particulate filter, nano-composites are new areas of research. Therefore, we reported the easy synthesis of spinel NiCo2O4/perovskite LaCoO3 nano-composite, and its individual oxides NiCo2O4 and LaCoO3 for comparison. The detailed insights into the physio-chemical characteristics of formed NiCo2O4/ LaCoO3 nano-composite were done based on various characterization analysis such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR), N2 physiosorption, scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The characterization analysis of NiCo2O4/LaCoO3 revealed the successful formation of a chemical interface possessing strong interfacial interaction, resulting in desirable physicochemical characteristics such as small crystallite size, abundant mesoporosity, high specific surface area and activation of surface lattice oxygen. Owing to the desirable characteristics, the activity results over NiCo2O4/LaCoO3 nano-composite showed the excellent CO oxidation performance and high soot oxidation activity, recyclability and thermal stability. This work mainly attempts to emphasize the effectiveness of the facile, inexpensive and conventionally used precipitation method for the successful formation of highly efficient nano-composites.

Dynamic Regulation Achieving High-Performance La-Containing Prussian Blue Analogues for Aqueous K+ Storage

Lanthanum (La), an "industrial aginomoto" element, exhibits that a small amount of introduction would greatly improve performance. However, La-containing Prussian blue analogues (PBAs) would be dissolved into aqueous solutions, which cannot act as a potassium-ion (K+) storage host. Here, an effective dynamic regulating strategy (chemical components and structures) is developed to overcome the high solubility of La-containing PBA in aqueous electrolytes and achieve high structural stability and superior aqueous K+ storage. For chemical component regulation, Fe3+ ions in the electrolyte fill the La3+ vacancies on the surface and the modified surface hinders the La atoms from further dissolving, and the remaining La atoms in bulk phase improve electron/ion transfer ability and amount of K+ storage. For the structure regulation, the material is transferred from the hexagon to the cubic lattice during charging-discharging procedures, achieving a highly thermodynamically optimal structure. The cathode presents ultrahigh capacities of 171, 155, 132, and 116 at current densities of 1, 2, 3, and 4 A g-1 respectively, and the capacity remains almost constant after 1000 cycles. The mechanism is revealed by experiments and density functional theory (DFT).

Activation of bisulfite by LaFeO3 loaded on red mud for degradation of organic dye

In this study, red mud (RM) was used as a support for LaFeO₃ to prepare LaFeO₃-RM via the ultrasonic-assisted sol-gel method for the removal of methylene blue (MB) assisted with bisulfite (BS) in the aqueous solution. Characterization by scanning electron microscopy and the Brunauer-Emmett-Teller method indicated that LaFeO₃-RM exhibited a large surface area and porous structure with a higher pore volume (i.e. 10 times) compared with the bulk LaFeO₃. The XRD, XPS and FTIR results revealed that the support of porous RM not only dispersed LaFeO₃ particles but also increased Fe oxidation capability, oxygen-containing functional groups and chemically adsorbed oxygen (from 44.3% to 90.3%) of LaFeO₃-RM, which improved the catalytic performance in structure and chemical composition. MB was removed through the synergistic effect of adsorption and catalysis, with MB molecules first absorbed on the surface and then degraded. The removal efficiency was 88.19% in the LaFeO₃-RM/BS system under neutral conditions but only 27.09% in the LaFeO₃/BS system. The pseudo-first-order kinetic constant of LaFeO₃-RM was six times higher than that of LaFeO₃. Fe(III) in LaFeO₃-RM played a key role in the activation of BS to produce SO 4 ⋅ - by the redox cycle of Fe(III)/Fe(II). Dissolved oxygen was an essential factor for the generation of SO 4 ⋅ - . This work provides both a new approach for using porous industrial waste to improve the catalytic performance of LaFeO₃ and guidance for resource utilization of RM in wastewater treatment.

Effect of Heat Treatment on Structural, Magnetic and Electrical Properties of La2FeMnO6

In this study, the effect of heat treatment on the structural, magnetic and electrical properties of La2FeMnO6 prepared via the sol-gel and sintering method were investigated. The heat-treatment conditions, i.e., the calcination temperature (1023 K and 1173 K), sintering temperature and time (1273 K for 1 and 3 h) were carried out. X-ray diffraction (XRD) revealed orthorhombic pnma (62) symmetry without any impurity phase for all samples. X-ray photoelectron spectroscopy confirmed the presence of Fe2+-Fe3+-Fe4+ and Mn3+-Mn4+ mixed states, and lanthanum and oxygen vacancies resulting in various magnetic exchange interactions. Furthermore, the magnetisation hysteresis showed enhanced hysteresis loops accompanied by an increase in magnetisation parameters with calcination temperature. The Raman phonon parameters induced a redshift in the phonon modes, alongside an increase in the intensity and compression of the linewidth, reflecting a decrease in lattice distortion, which was confirmed by XRD. The temperature-dependent conductivity showed that the conduction mechanism is dominated by p-type polaron hopping, and the lowest activation energy was approximately 0.237 ± 0.003 eV for the minimum heat-treatment conditions. These results show that varying heat-treatment conditions can significantly affect the structural, magnetic and electrical properties of the La2FeMnO6 system.

Boosting the surface oxygen activity for high performance Iron-based perovskite oxide

Surface oxygen activities always play an important role in various heterogeneous reaction processes. In this study, the surface oxygen activity of studied perovskite oxides is greatly enhanced after the composition and morphology are tuned. It is worth noting that the surface oxygen activity is enhanced correspondingly, accompanied by higher surface area, better reducibility, and superior low-temperature reactivity of studied catalysts. The sample introduced with nickel atom and nanorods structure possesses higher surface oxygen activity and vacancies with superior performance including T₁₀ at 221 °C and T₉₀ at 243 °C, nearly 90 °C elevations. Double perovskite oxides, especially with nanorods structure are verified to be composed of more surface active oxygen, which could be related to low-temperature redox ability and superior oxygen vacancies. Based on the DFT calculation, introducing nickel element is confirmed to be able to efficiently boost the generation of oxygen vacancies and adsorption of oxygen molecular, in accord with the analysis of characterization. To sum up, the strategy of introducing the nickel atom and nanorods structure could effectively tune the surface oxygen activity and generate more oxygen vacancies, which would be beneficial to the catalytic performance of toluene catalytic oxidation correspondingly.

Enhanced activation of peroxymonosulfte by LaFeO3 perovskite supported on Al2O3 for degradation of organic pollutants

In this study, the effect of various supports on activation of peroxymonosulfate and consequent degradation of Acid Orange 7 (AO7) in aqueous solutions was examined at the presence of LaFeO₃ perovskite as catalyst. Results showed that the AO7 degradation efficiency by LaFeO₃ supported on different supports was in an order of LaFeO₃/Al₂O₃ (86.2%) > LaFeO₃ (70.8%) > LaFeO₃/CeO₂ (59.0%) > LaFeO₃/SiO₂ (52.3%) > LaFeO₃/TiO₂ (32.2%). Moreover, the pseudo first-order rate constant for AO7 degradation by LaFeO₃/Al₂O₃ was 3.2 times than that by LaFeO₃. The enhancement was attributed to its large surface area, abundant chemisorbed surface-active oxygen, redox property and faster electron transfer. AO7 degradation and the leaching of iron ions decreased with the increase of pH. Data of electron spin resonance spectroscopy and quenching experiments revealed that sulfate and hydroxyl radicals were generated on LaFeO₃/Al₂O₃ surface, while sulfate radicals were identified to be the main reactive species responsible for AO7 degradation. Mechanisms for peroxymonosulfate activation were consequently proposed. Furthermore, LaFeO₃/Al₂O₃ catalyst exhibited a superior stability after five cycles. This work provides a new approach for design of iron-based perovskite catalysts with high and stable catalytic activity for removal of organic pollutants from aqueous solutions.

Catalytic Soot Oxidation Activity of NiO-CeO2 Catalysts Prepared by a Coprecipitation Method: Influence of the Preparation pH on the Catalytic Performance

A series of NiO-CeO2 mixed oxide catalysts have been synthesized by a modified coprecipitation method at three different pH values (pH = 8, 9, and 10). The NiO-CeO2 mixed oxide samples were characterized by TGA, XRD, inductively coupled plasma atomic emission spectroscopy (ICP-AES), FTIR, Brunauer-Emmett-Teller (BET) surface area, H2 temperature-programmed reduction (H2-TPR), and electron microscopy (high-angle annular dark-field transmission electron microscopy/energy-dispersive X-ray spectroscopy (HAADF-TEM/EDS)). The catalytic activities of the samples for soot oxidation were investigated under loose and tight contact conditions. The catalysts exhibited a high BET surface area with average crystal sizes that varied with the pH values. Electron microscopy results showed the formation of small crystallites (~5 nm) of CeO2 supported on large plate-shaped particles of NiO (~20 nm thick). XRD showed that a proportion of the Ni2+ was incorporated into the ceria network, and it appeared that the amount on Ni2+ that replaced Ce4+ was higher when the synthesis of the mixed oxides was carried out at a lower pH. Among the synthesized catalysts, Ni-Ce-8 (pH = 8) exhibited the best catalytic performance.

Porous LaFeO3 Prepared by an in Situ Carbon Templating Method for Catalytic Transfer Hydrogenation Reactions

Catalytic transfer hydrogenation is an attractive route for the synthesis of biomass-derived chemicals. However, development of efficient, low-cost, and stable catalysts for that reaction is still a challenge. Here, we report on the preparation and testing of a non-noble perovskite oxide (LaFeO₃) catalyst synthesized by an in situ carbon templating method. We show that our catalyst is quite active and selective toward the hydrogenation of unsaturated organics. Compared to an analogous LaFeO₃ catalyst prepared by a more traditional method, using citric acid, the new LaFeO₃ exhibited a more porous structure, a La-enriched surface composition, and abundant oxygen vacancies, all characteristics that improve contact with the reactants. In the case of the conversion of furfural to furfuryl alcohol (FOL) using iso-propanol as hydrogen donor, the new LaFeO₃ showed a furfural conversion of 90% and a selectivity to FOL of 94%, significantly higher than with the reference LaFeO₃ prepared by the traditional sol-gel method (60 and 91%, respectively). Moreover, our new LaFeO₃ catalyst can be recovered after a calcination treatment, with no appreciable changes in its structure or activity, a test that we repeated six times, and can promote the hydrogenation of other carbonyl compounds containing electron-withdrawing groups. A reaction mechanism is proposed in which metal cations are the adsorption sites for iso-propanol and oxygen vacancies are the adsorption sites for furfural, and where the conversion proceeds following an acid-base mechanism. We believe that the novel use of perovskites as catalysts for hydrogenation reactions reported here may be easily extendable to other processes, and that our carbon-templating synthetic approach offers a way to synthesize viable perovskite catalysts with high surface areas for optimized activity.

Macroporous SmMn2O5 mullite for NOx-assisted soot combustion

A series of mullite SmMn₂O₅ oxides were prepared by citric acid (CA), hydrothermal (HT) and co-precipitation (CP) and combustion of ethylene glycol and methanol solutions (EG&M) methods, and tested for NO_x-assisted soot combustion.

Preparation, characterization and catalytic application of hierarchically porous LaFeO3 from a pomelo peel template

Hierarchically porous LaFeO₃ perovskites are synthesized through a facile process by using pomelo peel as a biotemplate.

Activity and deactivation of Ru supported on La1.6Sr0.4NiO4 perovskite-like catalysts prepared by different methods for decomposition of N2O

Ru/La_1.6Sr_0.4NiO₄ prepared by the addition of ethylene glycol shows excellent activity for N₂O decomposition, even in the presence of O₂ and water.

Facile synthesis of three-dimensionally ordered macroporous silicon-doped La0.8K0.2CoO3 perovskite catalysts for soot combustion

Three-dimensionally ordered macroporous (3DOM) silicon-doped La_0.8K_0.2CoO₃ perovskite catalysts were successfully prepared by a colloidal crystal templating method. The catalysts showed a well-ordered macroporous structure and exhibited high activity for soot removal.

Sulfur resistant LaxCe1−xNi0.5Cu0.5O3 catalysts for an ultra-high temperature water gas shift reaction

Synergistic effect of Ni–Cu with La₂O₃–CeO₂ for high sulfur resistance in water gas shift reaction.