钙钛矿型稀土复合氧化物超细粒子对CO还原SO2的催化性能

以共沉淀－－超临界干燥法制钙钛矿型ＬａＣｏＯ３和ＬａＭｎＯ３稀土合氧化物超细粒子,测试了该超细粒子对ＣＯ还原Ｓ煌催化性能,发现随ＬａｃｏＯ３和ＬａＭｎＯ３颗粒粒径减小和比表面积增大其对ＣＯ还原Ｓ煌催化活性提高。反应产物证棂单质硫,有微量ＣＯＳ和ＣＳ２生成,其中ＣＯＳ可能是ＣＯ还原ＳＯ２生成单质硫过程中的中间产物。     

钙钛矿型氧化物LaFeO3光催化活性的研究

本文用柠檬酸络合法制备了ＬａＦｅＯ２及Ｌａ１－ｘＣａｘＦｅＯ３、ＬａＦｅ１－ｘＣｕｘＯ３等钙钛矿型复合氧化物。以这些氧化物作催化剂在荧光高压汞灯照射下进行水溶性染料光催化降解试验,探讨了掺杂对ＬａＦｅＯ３光催化活性的影响。     

钙钛矿型LaFeO3和SrFeO3的光催化性能

采用柠檬酸法合成钙钛矿型复合氧化物LaFeO3和SrFeO3,并以其为光催化剂对不同水溶性染料进行光催化降解实验.结果表明:SrFeO3的光催化活性明显高于LaFeO3,这与A位离子(La3+,Sr2+)的电子构型的不同有关.     

钙钛矿型稀土复合氧化物催化活性研究进展

概述了近年来对钙钛矿型稀土复合氧化物催化活性研究的进展。研究发现,与其他催化剂相比,钙钛矿型稀土复合氧化物作为燃烧催化剂时,特别是对大气污染物降解具有较好的催化活性,而钙钛矿型稀土复合氧化物作为光催化剂时,对水体污染物降解方面具有很好的光催化作用,具有很大的应用价值。     

稀土钙钛矿型复合氧化物催化剂研究现状(Ⅱ)

综述了近年来国内外稀土钙钛矿型复合氧化物的研究进展，研究了ABO，稀土钙钛矿型催化剂对各种气体的催化效果及反应机理，并讨论了催化剂的S与P的中毒机理。对稀土钙钛矿型催化剂的优缺点以及当前需要解决的问题进行了分析。     

稀土钙钛矿型复合氧化物催化剂研究现状(Ⅰ)

综述了近年来国内外稀土钙钛矿型复合氧化物的研究进展，阐述了由于ABO3稀土钙钛矿型催化剂A、B位的取代，出现了许多钙钛矿型及类似钙钛矿型晶体结构，增加了氧格空位，提高了钙钛矿型催化剂的催化活性。并且详细介绍了催化剂及其载体的制备方法及工艺。     

负载型La2-xSrxCoO4类钙钛矿复合氧化物CO催化氧化性能

采用柠檬酸络合-浸渍法制备了以镁铝尖晶石MgAl2O4为载体、复合氧化物La2-xSrxCoO4(X=0.2、0.4、0.6和0.8)为活性组分的催化剂,通过XRD、H2-TPR和BET等分析方法对催化剂进行表征,利用固定床微型反应器测试催化剂对CO氧化的催化性能,并考察水蒸汽和SO2对其活性的影响.结果表明,X=0....     

钙钛矿型复合氧化物催化剂应用研究进展

概述了钙钛矿型复合氧化物催化剂的结构特征,阐述了在光催化降解、汽车尾气净化、烟气催化脱硫、固体氧化物燃料电池以及固体推进剂催化燃烧等领域的应用研究进展,并分析了该类催化剂在各应用领域存在的技术难题以及发展前景.     

类钙钛矿型复合氧化物La_2NiO_4的制备和性能研究

采用共沉淀法、硝酸盐分解法、溶胶-凝胶法3种不同的方法制备了纳米级的类钙钛矿型复合氧化物La2NiO4;采用XRD、SEM、BET等实验技术对催化剂进行了表征,并且考察了该催化剂对CH4/CO2重整反应的催化活性。实验结果发现,不同方法制备的催化剂在粒子大小、比表面积、催化活性等方面存在差异,其中溶胶-凝胶法制备的催化剂表现较好。     

稀土钙钛矿型复合氧化物的制备及其在催化方面的研究进展

主要介绍了稀土钙钛矿型复合氧化物的结构及其主要制备方法,评述了各种制备方法的优劣.简述了目前国内外稀土钙钛矿型复合氧化物在催化方面的应用情况与研究进展,并对其前景进行了展望.     

Auto-combustion synthesis and characterization of perovskite-type LaFeO3 nanocrystals prepared via different routes

LaFeO₃ was prepared via simple, economical and environmentally friendly auto-combustion methods using different fuels, including citrate, urea, sucrose, egg whites, gelatin and chitosan. The prepared ferrites were systematically characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, high resolution transmission electron microscopy (HRTEM), vibrating sample magnetometry (VSM) and electrical measurements to study the impact of the synthetic routes on the various properties. XRD showed the formation of a single orthorhombic phase, except for the samples prepared via egg white, gelatin and urea methods, which indicated a secondary La₂O₂CO₃ phase. The FT-IR and TEM studies confirmed the formation of the phase. Differential thermal analysis-thermogravimetry techniques (DTA-TG) were used to characterize the auto-combustion process up to ferrite formation. The obtained unsaturated magnetization for all of the samples suggested the presence of anti-ferromagnetic ordering in addition to weak ferromagnetic ordering. The egg white method showed higher magnetization (1.78 emu/g), while the urea and chitosan methods indicated lower magnetization (0.13 emu/g). The coercivity measurements confirmed the presence of ferromagnetic/anti-ferromagnetic interfaces with higher values than those reported in the literature. The AC-conductivity measurements indicated semiconducting characteristics and exhibited a change in the conduction mechanism from hopping to polaron conduction by increasing the temperature. LaFeO₃ prepared via the egg white method indicated an anti-ferromagnetic/paramagnetic transition at approximately 715 K. The dielectric measurements confirmed the AC-conductivity results and exhibited values higher than those reported in the literature.     

Ionic/electronic mixed conduction relations in perovskite-type oxides by defect structure

Perovskite-type oxides La_1-aA_aM_1-bB_bO_3-x with A=Sr²⁺, Ln³⁺, Ce⁴⁺ and M=Fe, Co, Ga; B=Co, Fe, Mg were prepared in the concentration range a=0·1 to 1 mol and b=0·1 to 0·5 mol. Additionally, A-substoichiometric compositions were prepared. Preparation conditions for monophase materials and structure types of the perovskite were determined by X-ray investigation. The electrical conductivity as a function of pO₂ in the range 10⁵>pO₂>10⁻¹⁴ Pa and temperature (500 to 1000°C) was measured on ceramic shapes by a dc four-point technique in combination with solid electrolyte coulometry. The ionic part of conductivity in mixed conductors was determined by oxygen permeation measurements. The II–III-perovskites Sr(Co,Fe)O_3-x in their stabilized form are excellent mixed conductors (maximum 500 S cm⁻¹ at 400°C) and have up to 2 orders of magnitude higher oxygen ionic conductivity than the preferred III–III-perovskite La(Sr)Mn(Co)O_3-x. The oxygen ionic conductivity of the electrolyte La(Sr)Ga(Mg)O_3-x, was increased by doping with 0·1 mol Co. By applying higher Co or Fe doping concentrations the lanthanum gallate, becomes a mixed conductor.     

La1-xSrxMnO3钙钛矿复合氧化物研究进展

综述了钙钛矿型复合氧化物La1-xSrxMnO3的制备方法，分析各种制备方法与传统材料制备方法的差别；根据其结构和性能特点介绍了其主要应用方向。     

Studies of the activation process over Pd perovskite-type oxides used for catalytic oxidation of toluene

Calcined and reduced catalysts Pd/LaBO₃ (B = Co, Fe, Mn, Ni) were used for the total oxidation of toluene. Easiness of toluene destruction was found to follow the sequence based on the T₅₀ values (temperature at which 50% of toluene is converted): Pd/LaFeO₃ > Pd/LaMnO_3+δ > Pd/LaCoO₃ > Pd/LaNiO₃. In order to investigate the activation process (calcination and reduction) in detail, the reducibility of the samples was evaluated by H₂-TPR on the calcined catalysts. Additionally, characterization of the Pd/LaBO₃ (B = Co, Fe) surface was carried out by X-ray photoelectron spectroscopy (XPS) at each stage of the global process, namely after calcination, reduction and under catalytic reaction at either 150 or 200 °C for Pd/LaFeO₃ and either 200 or 250 °C for LaCoO₃. The different results showed that palladium oxidized entities were totally reduced after pre-reduction at 200 °C for 2 h (2 L/h, 1 °C/min). As LaFeO₃ was unaffected by such a treatment, for the other perovskites, the cations B are partially reduced as B³⁺ (B = Mn) or B²⁺ even to B⁰ (B = Co, Ni). In the reactive stream (0.1% toluene in air), Pd⁰ reoxidized partially, more rapidly over Co than Fe based catalysts, to give a Pd²⁺/Pd⁴⁺ and Pd⁰/Pd²⁺/Pd⁴⁺ surface redox states, respectively. Noticeably, reduced cobalt species are progressively oxidized on stream into Co³⁺ in a distorted environment. By contrast, only the lines characteristic of the initial perovskite lattice were detected by XRD studies on the used catalysts. The higher activity performance of Pd/LaFeO₃ for the total oxidation of toluene was attributed here to a low temperature of calcination and to a remarkable high stability of the perovskite lattice whatever the nature of the stream which allowed to keep a same palladium dispersion at the different stages of the process and to resist to the oxidizing experimental conditions. On the contrary, phase transformations for the other perovskite lattices along the process were believed to increase the palladium particle size responsible of a lower activity.     

Structural and catalytic properties of mesoporous nanocrystalline mixed oxides containing magnesium

Oxide compounds are promising catalysts for VOC flameless combustion. In this paper the catalyst properties of two Mg-containing oxide compounds with different crystalline structures and chemical compositions (Mg spinel ferrite and La–Pb–Mg–Mn–O perovskite) were investigated. The samples, prepared by a combined sol–gel and self-combustion method and heat treatment, were characterized using X-ray diffraction, scanning electron microscopy, EDAX spectroscopy, and BET analysis. The two samples have been catalytically tested in flameless combustion reaction of acetone, benzene and propane at atmospheric pressure. The results revealed a higher catalytic activity of the perovskite catalyst that may be ascribed to smaller crystallite size (26 nm), larger surface specific area (8.6 m²/g) and the presence of manganese cations with variable valence (Mn^3 +–Mn^4 +).     

Synthesis of LaFeO3 perovskite-type oxide via solid-state combustion of a cyano complex precursor: The effect of oxygen diffusion

The effect of oxygen diffusion on the thermal decomposition kinetics of La[Fe(CN)₆]·5H₂O has been explored. In particular, the critical conditions under which LaFeO₃ can be synthesized via solid-state combustion of this cyano complex precursor were analytically and numerically investigated. Thermal analysis experiments as well as simulations showed that the oxygen diffusion enhancement facilitates the formation of a self-propagating combustion front during the decomposition of La[Fe(CN)₆]·5H₂O. As a consequence, the sample undergoes local overheating that raises its temperature by several hundreds of degrees. This enables the production of LaFeO₃ perovskite-type oxide with a minimum contribution of external heat resources. Although the self-propagating high-temperature method has already proven to be successful for the synthesis of perovskite-type oxides from cyano complex precursors under oxygen atmosphere, we will show that under the appropriate settings, air can be used instead. Moreover, the temperature of the front is related to the ease of oxygen diffusion. Therefore, the surface area and the crystal size of LaFeO₃ perovskite-type powders obtained via solid state combustion have been controlled by controlling the gas flow rate at which the sample has been exposed during the treatment.     

Liquid phase catalytic oxidation of alcohols over mixed metal oxides

Oxidation of alcohols was studied over CoO–CeO₂ using tert-butyl hydroperoxide (TBHP) and n-hexane as a solvent in liquid phase reaction. The catalyst used for this synthetically useful transformation showed considerable level of reusability besides good activity.     

Simultaneous removal of nitrogen oxides and diesel soot particulates catalyzed by perovskite-type oxides

Perovskite-type oxides (ABO₃) catalyzed the simultaneous removal of NO_x and diesel soot particulates in the presence of oxygen, and were superior to transition metal simple oxides in the selectivity for NO_x reduction. Although the catalytic activity of perovskite-type oxides depended on both A-site and B-site cations, the substitution of potassium at A sites prominently promoted the oxidation of soot and the reduction of NO_x.     

Oxidation of methane over Pd/mixed oxides for catalytic combustion

Palladium catalysts supported on mixed oxides (Pd/Al₂O₃–MO_x; M=Co, Cr, Cu, Fe, Mn, and Ni) were investigated for the low-temperature catalytic combustion of methane. Although the surface area decreased with increasing NiO in Pd/mAl₂O₃–nNiO, Pd/Al₂O₃–36NiO demonstrated an excellent activity due to the small particle size of palladium. Also, the catalytic activity strongly depended on the composition of the support. Temperature-programmed desorption of oxygen revealed that the catalytic activity in the low-temperature region depends on the adsorption state of oxygen on palladium. The activity was enhanced when the amount of adsorbed oxygen increased. In-situ XRD analysis indicated that the PdO phase was thermally stabilized on Pd/Al₂O₃–36NiO.