Oxidative coupling of methane over oxide catalysts with layered structure

The catalytic properties of complex oxides with a layered structure Bi₂GeO₅, Bi₂SiO₅, Bi₄Ti₃O₁₂, Bi₂CaSrCu₃O₈+x and YBa₂Cu₃O₆+δ in oxidative coupling of methane (OCM) have been studied. Bi₂EO₅ metastable compounds have been found to possess the high activity and C₂-selectivity 53–70%. It has been assumed that the intergrowth boundaries for the Bi₂EO₅ decomposition products, on which active catalytic sites may be located, play a specific role on the catalytic performance of the oxides. Bi₄Ti₃O₁₂ and Bi₂CaSrCu₃O₈+x have close catalytic activity values but Bi₂CaSrCu₃O₈+x as well as YBa₂Cu₃O₆+δ are not selective in OCM reaction.     

Co3O4-Bi2O2CO3催化剂的制备及其光催化性能

以Bi(NO₃)₃·5H₂O、Co(CH₃COO)₂·4H₂O为原料,采用化学沉淀-水热法制备了Co₃O₄-Bi₂O₂CO₃异质结构复合半导体光催化剂,并通过X射线衍射仪（XRD）、扫描电镜（SEM）、X射线光电子能谱（XPS）、紫外可见漫反射光谱（DRS）、荧光光谱（PL）等手段对所合成的复合型催化剂进行了理化性能表征。研究结果表明：引入Co₃O₄没有改变Bi₂O₂CO₃物相结构,但促进了Bi₂O₂CO₃ 对可见光的吸收能力,提高了Bi₂O₂CO₃表面吸附氧物种的数量,抑制了光生载流子复合。复合光催化剂对罗丹明B（RhB）的光催化脱色实验显示引入Co₃O₄能够明显提高Bi₂O₂CO₃催化剂的光催化脱色能力。尤其是Co₃O₄引入量为0.6%的Co₃O₄-Bi₂O₂CO₃样品对罗丹明B染料的光催化脱色率可达到97%（模拟日光照射30min）。本文为复合型光催化剂制备提供了简单易行的技术路线,制备的新型半导体复合光催化剂Co₃O₄-Bi₂O₂CO₃在环境净化方面表现出了较好的应用前景。     

Synthesis of CeO2–MnOx mixed oxides and catalytic performance under oxygen-rich condition

Ce_0.5Zr_0.5O₂, Ce_0.5Zr_0.2Mn_0.3O₂ and Ce_0.5Mn_0.5O₂ were prepared by citric acid sol–gel method. The effect of manganese on the structural and redox properties of ceria-based mixed oxides was investigated by means of powder X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller analyses, temperature-programmed reduction and catalytic activity evaluation in the presence of excess O₂. The results showed that some Mn cations could enter into the ceria lattice to form solid solutions. Mn₃O₄ appeared due to the instability of the mixed oxides with increment of the Mn doping ratio while another oxide Mn₂O₃ is detected in the physical mixture of ceria and manganese oxide. These Mn-doped mixed oxides, especially Ce_0.5Mn_0.5O₂, presented better catalytic activities than Ce_0.5Zr_0.5O₂ and even Pt-loaded catalyst for total oxidation of C₃H₈ and oxidative sorption of NO in the presence of excess oxygen. The oxidation ability of Mn and the strong interaction between Mn and Ce were suggested to promote the oxygen storage/transport capacity of the mixed oxides as well as reactive adsorption of nitric oxide and hydrocarbons.     

Facile ultrasonic-assisted synthesis of micro–nanosheet structure Bi4Ti3O12/g-C3N4 composites with enhanced photocatalytic activity on organic pollutants

The Bi₄Ti₃O₁₂/g-C₃N₄ composites with microsheet and nanosheet structure were prepared through facile ultrasonic-assisted method. The SEM and TEM results suggested that the nanosheets g-C₃N₄ were stacked on the surface of regular Bi₄Ti₃O₁₂ sheets. Comparing with pure Bi₄Ti₃O₁₂ and g-C₃N₄, the Bi₄Ti₃O₁₂/g-C₃N₄ composites showed significant enhancement in photocatalytic efficiency for the degradation of RhB in solution. With the mass ratio of g-C₃N₄ increasing to 10 wt%, the Bi₄Ti₃O₁₂/g-C₃N₄-10% presented the best photocatalytic activity. Its photocatalysis reaction constant was approximately 2 times higher than the single component Bi₄Ti₃O₁₂ or g-C₃N₄. Meanwhile, good stability and durability for the Bi₄Ti₃O₁₂/g-C₃N₄-10% were confirmed by the recycling experiment and FT-IR analysis. The possible mechanism for the improvements was the matched band positions and the effective separation of photo-excited electrons (e^-) and holes (h⁺). Furthermore, based on the results of active species trapping, photo-generated holes (h⁺) and superoxide radical (·O₂^-) could be the main radicals in reaction.     

Layered bismuth oxide/bismuth sulfide supported on carrageenan derived carbon for efficient carbon dioxide electroreduction to formate

Electrochemical reduction of carbon dioxide (CO₂ER) into formate plays a crucial role in CO₂ conversion and utilization. However, it still faces the problems of high overpotential and poor catalytic stability. Herein, we report a hybrid CO₂ER electrocatalyst composed of layered bismuth sulfide (Bi₂S₃) and bismuth oxide (Bi₂O₃) supported on carrageenan derived carbon (Bi-CDC) prepared by a combined pyrolysis with hydrothermal treatment. In such 3D hybrid, layered Bi₂O₃ and Bi₂S₃ are uniformly grown on nanocarbon supports. Benefiting from strong synergistic effect between Bi₂O₃/Bi₂S₃ and nanocarbon, Bi-CDC-1:2 displays a high Faradic efficiency (FE) of >80% for formate production in the range of -0.9 V to -1.1 V with the maximum formate FE of 85.6% and current density of 14.1 mA·cm^-2 at -1.0 V. Further, a positive onset potential of -0.5 V, a low Tafel slope of 112.38 mV·dec^-1, and a slight performance loss during long-term CO₂ER tests are observed on Bi-CDC-1:2. Experimental results shows that the better CO₂ER performance of Bi-CDC-1:2 than that of Bi₂O₃ can be attributed to the strong interfacial interactions between nanocarbons and Bi₂O₃/Bi₂S₃. In situ ATR-FTIR measurements reveal that the rate-determining step in the CO₂ER is the formation of HCOO* intermediated. Compared with carbon support, Bi-CDC-1:2 can promote the production of HCOO* intermediate and thus promoting CO₂ER kinetic.     

Evaluation of the role played by bismuth molybdates in Bi2Sn2O7–MoO3 catalysts used for partial oxidation of isobutene to methacrolein

The catalytic behaviour of multiphasic catalysts based on -bismuth pyrostannate, Bi₂Sn₂O₇, was investigated in the selective oxidation of isobutene into methacrolein. When -Bi₂Sn₂O₇ is mixed with MoO₃, strong cooperation effects on the yield and selectivity in methacrolein occur. However, XRD analyses performed on samples after test revealed the formation of a low quantity of -bismuth molybdate, -Bi₂Mo₃O₁₂, when the reaction temperature exceeded 673 K. Additional experiments were therefore carried out on the “Bi–Sn–Mo–O” catalysts in order to shed light on the role of Bi₂Mo₃O₁₂ in the synergetic effects observed in the Bi₂Sn₂O₇–MoO₃ system. The experimental results are discussed in terms of several hypotheses. First, the intrinsic activity of Bi₂Mo₃ O₁₂ is probably the simplest explanation for the synergetic effects, although experiments have shown that this phase present in a low quantity is only poorly active. Second, catalytic tests made on Bi₂Sn₂O₇–Bi₂Mo₃O₁₂ mechanical mixtures have evidenced a cooperation between these two ternary oxides, particularly when Bi₂Sn₂O₇ was the major component of the mixture. Consequently, it is likely that a synergy between Bi₂Sn₂O₇ and the in situ generated Bi₂Mo₃O₁₂ might play a role in the synergy observed in the Bi₂Sn₂O₇–MoO₃ association. Third, as bismuth pyrostannate was previously shown to behave as an oxygen donor phase with respect to WO₃, a remote control mechanism could therefore occur between Bi₂Sn₂O₇ and MoO₃, independently from the formation of -Bi₂Mo₃O₁₂.     

An investigation of NO/CO reaction over perovskite-type oxide La0.8Ce0.2B0.4Mn0.6O3 (B = Cu or Ag) catalysts synthesized by reverse microemulsion

The perovskite-type oxides La_0.8Ce_0.2Cu_0.4Mn_0.6O₃ and La_0.8Ce_0.2Ag_0.4Mn_0.6O₃ prepared by reverse microemulsion and sol–gel methods (denoted as R and S, respectively), have been investigated on their catalytic performance for the (NO + CO) reaction, and characterized by means of temperature-programmed desorption (TPD), X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). XRD measurements proved the presence of the perovskite phase with a considerable amount of CeO₂ phase and the formation of CeO₂ phase was restrained with the reverse microemulsion method. TEM investigations revealed that the La_0.8Ce_0.2Cu_0.4Mn_0.6O₃-R nanoparticles were uniform spheres in shape with diameters ranging from 40 to 50 nm, whereas an aggregation of particles was found for the La_0.8Ce_0.2Cu_0.4Mn_0.6O₃-S catalyst. The activity of NO reduction with CO decreased in the order of La_0.8Ce_0.2Cu_0.4Mn_0.6O₃-R > La_0.8Ce_0.2Cu_0.4Mn_0.6O₃-S > La_0.8Ce_0.2Ag_0.4Mn_0.6O₃-R > La_0.8Ce_0.2Ag_0.4Mn_0.6O₃-S. In NO-TPD experiments, the principal desorbed species detected in the effluent was NO with a trace amount of O₂ and N₂O, suggesting that the non-dissociated adsorption of NO on the surface of the perovskite-type oxides was dominant. The XPS results revealed that Ce⁴⁺ and Cu⁺ was the predominant oxidation state for Ce and Cu components in La_0.8Ce_0.2Cu_0.4Mn_0.6O₃ and La_0.8Ce_0.2Ag_0.4Mn_0.6O₃ catalysts. The existence of Cu⁺ ions and its redox reaction (Cu⁺ ↔ Cu²⁺) would benefit the NO adsorption and reduction by CO.     

Bi12TiO20 synthesized directly from bismuth (III) nitrate pentahydrate and titanium glycolate and its activity

Pure phase of sillenite structure, Bi₁₂TiO₂₀, was directly synthesized using stoichiometric bismuth (III) nitrate pentahydrate and titanium glycolate by co-precipitation. The influence of pH on the structure of Bi₁₂TiO₂₀ was studied in the pH range of 3–10. The sillenite structure was characterized using XRD and FTIR. The photo-degradation reaction of 4-nitrophenol (4-NP) was used to study photocatalytic activity of Bi₁₂TiO₂₀ as a function of the preparation pH. The rate of decomposition was followed by UV-vis and TOC. The beginning concentration of 4-NP, 44 ppm, decreased to less than 1 ppm within 30 min for all prepared catalysts. It was found that the decomposition rate constant of Bi₁₂TiO₂₀ is six times higher than those of either TiO₂ or Bi₂O₃ under the same conditions.     

Physico-chemical properties of V-Sb-oxide systems and their catalytic behaviour in oxidative dehydrogenation of light paraffins

Catalysts prepared as bulk VSb_0.1O_x and supported V₂O₅/Al₂O₃, V₂O₅-Sb₂O₃/Al₂O₃ and Sb₂O₃/Al₂O₃ (containing 0.5, 1 or 2 theoretical monolayers of V₂O₅ or Sb₂O₃) were tested in the oxidative dehydrogenation of iso-butane at 550°C in i-C₄H₁₀:O₂:He=20:10:70 gas mixture. Fresh and used catalysts were characterised by BET, XRD and XPS. Reactivity and thermochemistry of active oxygen taking part in the redox cycle with ethane and hydrogene were studied using in situ differential scanning calorimetry. Temperature-programmed desorption of O₂ in He flow was also investigated and in situ DRIFT was applied to investigate surface species of the catalysts in flows of i-C₄H₁₀, O₂ and i-C₄H₁₀/O₂ mixture. Supported VSb_yO_x catalysts are more active and selective than bulk one. V-only supported catalysts display a high efficiency due to the high reactivity of VOX-species. In bulk catalyst, the surface is enriched with antimony. In supported samples, the surfaces V/Sb are close to the calculated ones. In the presence of antimony, the amount of active oxygen species and their reactivity in redox transformation is improved. The rates of vanadium reduction and reoxidation are also higher. Compared to V-only catalysts, supported V-Sb-catalysts display a lower coking activity and higher on-stream stability.     

Influence of oxygen supply rates on performances of catalytic membrane reactors: Application to the oxidative coupling of methane

The impact of oxygen permeability using an ionic oxygen conducting membrane reactor with surface catalyst was investigated for the oxidative coupling of methane to higher hydrocarbons. Dense Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO), Ba_0.5Sr_0.5Mn_0.8Fe_0.2O_3−δ (BSMFO) and BaBi_0.4Fe_0.6O₃ (BBFO) membrane disks with Pt/MgO catalysts were prepared by sol–gel deposition or wash-coating. It is demonstrated that the oxygen supply by permeation needs to fit to the consumption during the coupling reaction. In case of insufficient oxygen supply comparably poor conversions are observed while higher oxygen fluxes lead to increased methane conversions, especially in the presence of an efficient catalyst. Generally, increasing catalytic activity leads to lower C₂ selectivity, especially for low oxygen permeation fluxes. The concept of a reactor employing dense catalytic membranes is viable, but the present study identifies further potential when the activity of the catalyst for the oxidative coupling is improved, leading to an overall enhanced performance of the membrane reactor.     

Bi2O2CO3/Fe3O4磁性复合物在环境污染治理领域中的应用

以Fe₃O₄纳米粒子和Bi₂O₂CO₃为原料,采用溶剂热法制备Bi₂O₂CO₃/Fe₃O₄磁性复合物,并通过对印染废水中染料的去除、剩余污泥厌氧消化过程中产甲烷潜力的影响两方面探讨其在环境污染治理中的应用。借助X射线衍射（XRD）、扫描电镜（SEM）、傅里叶红外光谱（FTIR）和比表面积及孔径分析对Bi₂O₂CO₃/Fe₃O₄复合物进行表征分析,SEM分析结果表明复合物表面较粗糙,BET结果显示复合物的比表面积为9.2294m²/g,Fe₃O₄的引入大幅度增加了Bi₂O₂CO₃的比表面积,使其具有明显的介孔结构。一方面,以甲基橙（MO）为目标污染物,研究了不同实验条件下该材料对染料的去除效果,结果表明,最大吸附量可达14.373mg/g,且该吸附反应过程符合拟二级动力学和Langmuir吸附等温模型,趋于单分子层吸附;另一方面,评估了复合物对污泥厌氧消化产甲烷潜力的影响,结果表明,复合物的引入对污泥厌氧消化产甲烷过程有一定的促进作用,累积产甲烷量相比于对照组提高了10%。分别用一级动力学模型和修正Gompertz模型模拟厌氧消化过程,模拟结果显示一级动力学模型可以更好地描述引入Bi₂O₂CO₃/Fe₃O₄磁性复合物的污泥厌氧消化过程。     

Facile synthesis of spinel LiNi0.5Mn1.5O4 as 5.0 V-class high-voltage cathode materials for Li-ion batteries

LiNi_0.5Mn_1.5O₄ and LiMn₂O₄ with novel spinel morphology were synthesized by a hydrothermal and post-calcination process. The synthesized LiMn₂O₄ particles (5-10 μm) are uniform hexahedron, while the LiNi_0.5Mn_1.5O₄ has spindle-like morphology with the long axis 10-15 μm, short axis 5-8 μm. Both LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ show high capacity when used as cathode materials for Li-ion batteries. In the voltage range of 2.5-5.5 V at room temperature, the LiNi_0.5Mn_1.5O₄ has a high discharge capacity of 135.04 mA·h·g^-1 at 20 mA·g^-1, which is close to 147 mA·h·g^-1 (theoretical capacity of LiNi_0.5Mn_1.5O₄). The discharge capacity of LiMn₂O₄ is 131.08 mA·h·g^-1 at 20 mA·g^-1. Moreover, the LiNi_0.5Mn_1.5O₄ shows a higher capacity retention (76%) compared to that of LiMn₂O₄ (61%) after 50 cycles. The morphology and structure of LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ are well kept even after cycling as demonstrated by SEM and XRD on cycled LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ electrodes.     

New insights in the understanding of the behaviour and performances of bismuth molybdate catalysts in the oxygen-assisted dehydration of 2-butanol

Pure Bi₂Mo₃O₁₂, Bi₂Mo₂O₉, Bi₂MoO₆, MoO₃ and -Sb₂O₄ and their mechanical mixtures were investigated in the oxygen-assisted dehydration of 2-butanol at atmospheric pressure and at low temperature (220 and 250°C). All catalysts were characterized before and after the catalytic reaction by BET surface area measurement, Raman spectroscopy, XRD and XPS. A strong parallelism is confirmed with the results obtained in the selective oxidation of olefins. In the frame of the remote control concept, , β and γ-bismuth molybdates are able to play a dual role: donor of spillover oxygen (Oso) with respect to MoO₃, and acceptor of Oso with respect to -Sb₂O₄. On one hand, this duality leads to mutual increase of activity when the bismuth molybdates are mixed together. In the presence of MoO₃, the phase seems to be a stronger Oso donor than β and γ, and β has a donor strength between and γ. On the other hand, when the Bi molybdates are reacted in the presence of a big quantity of spillover oxygen, like in a mixture with -Sb₂O₄, they undergo a dramatic decrease of activity. The phenomenon originates from the full oxidation of the reduced Mo species to Mo⁶⁺ induced by Oso. In parallel with other reactions involving oxygen, this confirms that the real active and selective state of molybdenum-containing oxides is that slightly reduced possessing Mo⁵⁺.     

Piezocatalytic performance of Fe2O3−Bi2MoO6 catalyst for dye degradation

A Fe₂O₃−Bi₂MoO₆ heterojunction was synthesized via a hydrothermal method. Scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray, powder X-ray diffraction, Fourier transform infrared spectroscopy and ultra-violet−visible near-infrared spectrometry were performed to measure the structures, morphologies and optical properties of the as-prepared samples. The various factors that affected the piezocatalytic property of composite catalyst were studied. The highest rhodamine B degradation rate of 96.6% was attained on the 3% Fe₂O₃−Bi₂MoO₆ composite catalyst under 60 min of ultrasonic vibration. The good piezocatalytic activity was ascribed to the formation of a hierarchical flower-shaped microsphere structure and the heterostructure between Fe₂O₃ and Bi₂MoO₆, which effectively separated the ultrasound-induced electron–hole pairs and suppressed their recombination. Furthermore, a potential piezoelectric catalytic dye degradation mechanism of the Fe₂O₃−Bi₂MoO₆ catalyst was proposed based on the band potential and quenching effect of radical scavengers. The results demonstrated the potential of using Fe₂O₃−Bi₂MoO₆ nanocomposites in piezocatalytic applications.     

镍锰酸锂正极材料及其适配性电解液研究最新进展

随着新能源汽车产业的蓬勃发展,对高能量密度动力电池的需求日益迫切。开发高电压正极材料及其适配性电解液,成为下一代高能量密度动力电池的主要研究方向。镍锰酸锂（LiNi_0.5Mn_1.5O₄）材料以其高电压（4.7 V,vs.Li/Li ⁺）、高能量密度（达650 W·h/kg）、资源丰富且价格低廉而受到广泛关注。然而,镍锰酸锂材料在长期的充放电循环过程中,锰从电极材料中溶解,破坏了电极材料的结构,导致电池性能恶化。介绍了镍锰酸锂正极材料及其适配性电解液研究最新进展。指出离子掺杂、表面包覆、复合方法是改善镍锰酸锂电化学性能的有效途径。同时,通过引入成膜添加剂、改变锂盐的种类及浓度、调整主溶剂的种类及比例等方法,可以提高电解液的耐高压性能,提高镍锰酸锂电极与电解液的界面稳定性,也是提升镍锰酸锂电池性能的重要方法。最后提出,适用于锂离子电池的5 V高电压电解液的研发相对滞后,其是制约高电压电池体系应用的主要问题。     

界面化学对镍锰酸锂正极材料电化学性能影响的研究现状及分析

尖晶石LiNi_0.5Mn_1.5O₄正极材料因理论比容量和理论比能量高、工作电压高、资源丰富且价格低廉等优点而备受关注,但该材料因为高电压下电解液的分解及界面副反应导致循环性能和倍率性能不佳,制约着材料的推广应用。结合近几年的研究报道,介绍了LiNi_0.5Mn_1.5O₄正极材料的结构及脱嵌机制、表/界面化学、改性方法,着重介绍了LiNi_0.5Mn_1.5O₄材料的表面性质及不同组分之间的界面反应机制及对正极材料电化学性能的影响,指出LiNi_0.5Mn_1.5O₄材料的晶面取向、颗粒形貌、表面元素分布、包覆及离子掺杂是改善镍锰酸锂材料电化学性能的有效途径。同时,通过溶剂替代、成膜添加剂的添加、改变锂盐的种类及浓度等方式,开发与之匹配的耐高压电解液也是提升镍锰酸锂电池性能的重要方法。最后,对LiNi_0.5Mn_1.5O₄正极材料表面改性和电解液界面构筑方面进行了总结和展望,旨在为提升该材料性能的相关研究提供参考。     

离子液体作为电解液添加剂用于高压锂离子电池

合成了功能化离子液体1-丁基-3-甲基咪唑双（三氟甲磺酰）亚胺盐（BMIMTFSI）作为高压锂离子电池电解液添加剂,用于抑制有机溶剂的氧化,以提高碳酸酯类电解液的耐高压性。分别采用充放电测试、电化学交流阻抗（EIS）、循环伏安法（CV）和扫描电子显微镜（SEM）等研究了LiNi_0.5Mn_1.5O₄/Li电池的电化学行为和LiNi_0.5Mn_1.5O₄材料表面形貌。结果表明,当在电解液中添加20% （体积分数）BMIMTFSI时,LiNi_0.5Mn_1.5O₄/Li电池在室温、0.2C下的最高放电比容量是126.81 mA·h·g^-1,5C下的放电比容量为109.36 mA·h·g^-1,比在1 mol·L^-1 LiPF₆-EC/DMC电解液中的放电比容量提高了91.7%;且该电池在0.2C下循环50圈后的放电比容量保持率在95%左右,比用碳酸酯类电解液提高了近10%。SEM结果表明,在碳酸酯类电解液中加入BMIMTFSI后,LiNi_0.5Mn_1.5O₄电极表面附着了一层均匀且致密的固态电解质界面（SEI）膜。     

Effect of the support and added oxides on the bistability observed in the oxidative dehydrogenation of 2-propanol over copper-supported catalysts

A bistability phenomenon has been observed in the oxidative dehydrogenation of 2-propanol over supported copper catalysts. Cu/Al₂O₃ and Cu/CeO₂ have been prepared by room temperature adsorption of the copper amino complex on the supports. The comparison of the hysteresis observed when the partial pressure of oxygen is varied, indicates that there is an important effect of the support. This effect is explained by the variation in specific surface areas of the supports and in their reducibilities. The possible influence of a second phase (-Sb₂O₄, SnO₂, Bi₂O₃ and NiO) added to the copper catalysts has also been studied.     

Grain growth in TiO2-added ZnO–Bi2O3–CoO–MnO ceramics prepared by chemical processing

The effect of TiO₂ on the grain growth of the ZnO–Bi₂O₃–CoO–MnO ceramic system prepared by chemical coprecipitation, was studied between 1150 and 1300 °C in air. Bi₂O₃ melts during firing, and then TiO₂ dissolves into Bi₂O₃-rich liquid. TiO₂ initially reacts with Bi₂O₃ to form Bi₄Ti₃O₁₂. Above ≈1050 °C, Bi₄Ti₃O₁₂ reacts with ZnO to form Zn₂TiO₄ spinel phase. The kinetic study of grain growth carried out using the expression Gⁿ–G_oⁿ=K_o·t·exp(−Q/RT) gave grain exponent (n) value as 6 and the apparent activation energy (Q) as 226.46 kJ/mol. 1.00 mol% TiO₂ addition increased the grain growth exponent value from 6 to 7 and apparent activation energy with 1.00 mol% TiO₂ addition was found to be 197.10 kJ/mol. The ZnO grain size gradually increases with increasing TiO₂ content. Addition of TiO₂ may increase the reactivity of the Bi₂O₃-rich liquid towards the ZnO grain, thus affecting the ZnO grain growth.     

Reduction of LaMnO3. Structural features of phases La8Mn8O23 and La4Mn4O11

Two new phases with ordered anion vacancies, La₈Mn₈O₂₃ and La₄Mn₄O₁₁, both having the general formula A_nB_nO_3n·1, form during the reduction of perovskites of the type LaMnO_3.07. The solid LaMnO_3.07, obtained in air at 1100°C and subsequently reduced in flowing carbon monoxide at 350°C, gives the stoichiometric perovskite LaMnO_3.00, whose reduction starts at 420°C and is completed at 450°C with formation of the phase La₈Mn₈O₂₃. The second reduction stage starts at approximately 500°C and is completed at 520°C with formation of La₄Mn₄O₁₁. The solids in the range of composition LaMnO_3.00-La₈Mn₈O₂₃ and La₈Mn₈O₂₃-La₄Mn₄O₁₁ would seem by X-ray examination to be biphasic but the behaviour during reduction is typical of a monophasic substance, the oxygen pressure of which at constant temperature progressively decreases as the composition tends to the limiting values La₈Mn₈O₂₃ and La₄Mn₄O₁₁. The crystal lattice of La₈Mn₈O₂₃ can be considered as resulting from a sequence of seven octahedral sheets, MnO₆, alternated with tetrahedral sheets, MnO₄, and the crystal lattice of La₄Mn₄O₁₁ from a sequence of three MnO₆ sheets alternating with MnO₄ sheets.