Surface acidity study of Mn+-montmorillonite clay catalysts by FT-IR spectroscopy: Correlation with esterification activity

A simple method for evaluating the surface acidity of different cation-exchanged montmorillonite (mont) clay catalysts, Mⁿ⁺-mont (Mⁿ⁺=Al³⁺, Fe³⁺, Cr³⁺, Zn²⁺, Ni²⁺, Cu²⁺, and H⁺), involving treatment with pyridine is described. After treating with pyridine, the samples were heated at 120 °C and the FT-IR spectra were directly recorded in the region 1650 and 1350 cm⁻¹. The data obtained show the presence of both Lewis and Brønsted acid sites. The activities of the catalysts to bring about Brønsted acid catalysed esterification of succinic acid with iso-butanol to yield di-(iso-butyl) succinate have been studied. The Brønsted acidity data obtained for Mⁿ⁺-mont correlated well with activity in the esterification reaction. The activities of the catalysts were found to decrease in the order of exchange ions Al³⁺ > Fe³⁺ > Cr³⁺ > Zn²⁺ > Ni²⁺ > Cu²⁺ > Na⁺-mont. They also correlated well with the charge to radius ratio of the cations. The catalysts exchanged with trivalent cations showed stronger absorption bands attributed to Brønsted acidity (1540 cm⁻¹) whereas those exchanged with divalent cations showed an increased Lewis acidity (1450 cm⁻¹) and reduced Brønsted acidity along with charge to radius ratio. Zn²⁺-, Cu²⁺- and Ni²⁺-exchanged clays showed an additional peak around 1605 cm⁻¹ which is attributed to the pyridine adsorption on surface sites through its π electrons. The method suggested here to evaluate the acidity is suitable for active sites which are thermally unstable such as water molecules in the hydration shell of a cation in exchanged clay.     

基于总有界变分的森林火灾烟雾图像检测方法

森林火灾烟雾浓度升高时,所对应的图像模糊程度升高,总有界变分会逐渐下降,基于变分的特征性质,可以将边界之 间的差异有效表征出来。 由此,提出一种基于总有界变分的森林火灾烟雾图像检测方法。 以分块平稳分析的思想对目标函数 求极值,得到总有界值,通过两次比较总有界变分值从分块结果图中提取疑似烟雾分块,利用特征数据的融合聚类处理获得最 终的疑似烟雾区域。 为了得到更好的烟雾检测效果,对疑似烟雾特征区域进行运动特性分析,融合判定烟雾区域,给出火灾报 警。 算法屏蔽了对烟雾静态特征的复杂计算,在对疑似烟雾特性进行分析时,只需关注其运动特征便可以准确进行烟雾检测输 出,避免了繁琐计算带来的误差,对比验证效果显示,算法结果输出高效稳定。     

Photocatalytic activity of titania modified mesoporous silica for pollution control

A series of titania modified mesoporous silicates with variable Si/Ti ratios were prepared using titanium tetrabutoxide by impregnation method. The samples were characterized by different analytical techniques such as XRD, TEM, FT-IR, low temperature N₂ sorption, and UV–Vis diffused reflectance spectroscopy. The TiO₂ supported on mesoporous silica was found to be in the anatase form. Crystallite size calculated using Scherrer’s formula was found to be in the range 18–20 nm. However, the TiO₂ particle diameter estimated by TEM was 5 nm. UV–Vis spectra showed a blue-shift of the absorption edge for all the samples. The BET surface area decreased with TiO₂ loading. Photodegradation of basic dye-like methylene blue (MB) was studied on these titania modified mesoporous silica using UV irradiation. Volatile organic pollutants like phenol and toluene can also be photocatalytically degraded using these titania modified mesoporous silicates.     

Highly durable Sr-doped LaMnO3-based cathode modified with Pr6O11 nano-catalyst for protonic ceramic fuel cells based on Y-doped BaZrO3 electrolyte

Sr-doped LaMnO₃ (LSM) is one of the state-of-the-art cathodes with outstanding chemical stability but suffers from poor electrochemical activity. It is promising that LSM can be used as good cathode for protonic ceramic fuel cells (PCFCs), provided that its catalytic activity can be improved. Herein, we have developed a high-performance and durable LSM-based cathode used for PCFCs with stable Y-doped BaZrO₃ electrolyte. In this work, commercial LSM cathode is mixed with high-performance BaZr_0.85Y_0.15O_3-δ particles. Pr₆O₁₁ nano-catalysts are homogeneously dispersed into the composite cathode, resulting in a significant decrease in the cathode polarization resistance from 0.51 to 0.12 Ω·cm² at 600 °C. The power output improves by ~96% at 600 °C. Distribution of relaxation time analysis indicates that the processes of oxygen adsorption/dissociation and oxygen species diffuse to triple phase boundary sites are significantly promoted by Pr₆O₁₁. Furthermore, the 100 h stability tests show that the modified cathode is extremely stable.     

Personnel Selection Using Interval 2‐Tuple Linguistic VIKOR Method

Personnel selection is a very important activity in the human resource management of an organization. However, in many practical circumstances, due to time pressure and lack of information about candidates, decision makers generally tend to provide linguistic assessments and use different linguistic term sets to express their opinions during the personnel selection process. In this article, the VIKOR method combined with interval 2‐tuple linguistic variables is proposed to choose appropriate individuals among candidates in a group decision‐making environment. The interval 2‐tuple linguistic variable, which comprises two linguistic terms and two real numbers, is more flexible and precise to deal with linguistic information in solving personnel selection problems. To demonstrate the applicability and effectiveness of the proposed interval 2‐tuple linguistic VIKOR method, a numerical example of personnel selection in a tertiary care hospital is provided.     

Advanced fuel cell based on semiconductor perovskite La–BaZrYO3-δ as an electrolyte material operating at low temperature 550 °C

As an electrolyte, enough ionic conductivity, either proton (H⁺) or oxide (O²⁻) conduction, has demanded the better performance of low-temperature (especially below 550 °C) solid oxide fuel cell (LT-SOFCs). Notably, that either conductivity, higher performance, reliability, or higher cost is hampering the LT-SOFC marketing. In our current subject, we report the La-doped BZY proton conductor as an electrolyte has exhibited high ionic conductivity of 0.15 S/cm with a higher performance of 0.78 W/cm² at 550 °C. Also, the performance of LBZY is superior to the un-doped BZY electrolyte. Such high performance mainly ascribed due to the doping of La into BZY. Besides, the mechanism for high ion conductivity is explained. This work manifests that using the LBZY semiconductor perovskite as an electrolyte is more suitable for fuel cell technology.     

Oxygen ionic transport in SrFe1−yAlyO3−δ and Sr1−xCaxFe0.5Al0.5O3−δ ceramics

The oxygen permeability of mixed-conducting Sr_1−xCa_xFe_1−yAl_yO_3−δ (x=0–1.0; y=0.3–0.5) ceramics at 850–1000 °C, with an apparent activation energy of 120–206 kJ/mol, is mainly limited by the bulk ionic conduction. When the membrane thickness is 1.0 mm, the oxygen permeation fluxes under pO₂ gradient of 0.21/0.021 atm vary from 3.7×10⁻¹⁰ mol s⁻¹ cm⁻² to 1.5×10⁻⁷ mol s⁻¹ cm⁻² at 950 °C. The maximum solubility of Al³⁺ cations in the perovskite lattice of SrFe_1−yAl_yO_3−δ is approximately 40%, whilst the brownmillerite-type solid solution formation range in Sr_1−xCa_xFe_0.5Al_0.5O_3−δ system corresponds to x>0.75. The oxygen ionic conductivity of SrFeO₃-based perovskites decreases moderately on Al doping, but is 100–300 times higher than that of brownmillerites derived from CaFe_0.5Al_0.5O_2.5+δ. Temperature-activated character and relatively low values of hole mobility in SrFe_0.7Al_0.3O_3−δ, estimated from the total conductivity and Seebeck coefficient data, suggest a small-polaron mechanism of p-type electronic conduction under oxidising conditions. Reducing oxygen partial pressure results in increasing ionic conductivity and in the transition from dominant p- to n-type electronic transport, followed by decomposition. The low-pO₂ stability limits of Sr_1−xCa_xFe_1−yAl_yO_3−δ seem essentially independent of composition, varying between that of LaFeO_3−δ and the Fe/Fe_1−γO boundary. Thermal expansion coefficients of Sr_1−xCa_xFe_1−yAl_yO_3−δ ceramics in air are 9×10⁻⁶ K⁻¹ to 16×10⁻⁶ K⁻¹ at 100–650 °C and 12×10⁻⁶ K⁻¹ to 24×10⁻⁶ K⁻¹ at 650–950 °C. Doping of SrFe_1−yAl_yO_3−δ with aluminum decreases thermal expansion due to decreasing oxygen nonstoichiometry variations.     

PyC interphase growth mechanism and control models of C/SiC composites

To better understand the pyrocarbon (PyC) interphase growth mechanism, a series of experiments was conducted on the PyC deposited on T-300™ and T-700™ carbon fibers by the chemical vapor infiltration (CVI) method. Nine groups of fabrication parameters were used to analyze the effects of deposition temperature, pressure, and residence time on the PyC interphase growth mechanism. Atomic force microscopy (AFM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), Raman spectroscopy, and nanoindentation tests were performed to characterize the microstructures of carbon fibers and PyC interphase. The PyC interphase growth mechanism was discussed, and the relationships between the fabrication parameters, R (C₂/C₆) value, texture type, and interphase thickness were established through numerical simulations. The hardness and modulus of PyC for T-300™ and T-700™ carbon fibers were measured. The tensile behaviors of C/SiC minicomposites with medium and high textures PyC interphases were analyzed. The C/SiC composite with the medium texture PyC interphase possessed the higher fracture strength and failure strain with a longer fiber pullout length at the fracture surface.     

Structures and hydrogen storage properties of AeVH3 (Ae = Be,Mg, Ca,Sr) perovskite hydrides by DFT calculations

The capability of hydrogen to be an energy source has made the hydrogen storage as one of the most investigated research fields during the recent years, and novel perovskite materials have become the current focus for hydrogen storage applications. Here we study the AeVH₃ (Ae = Be, Mg, Ca, Sr) perovskite-type hydrides to explorer their potential for hydrogen storage applications using the density functional theory (DFT) implemented CASTEP code along with exchange correlation potential. The study examines the electronic structure, optical properties, elastic features and mechanical stability of the materials. The crystal structure of AeVH₃ compounds is found to be cubic with lattice constant as 3.66, 3.48, 3.76 and 3.83 for Ae = Be, Mg, Ca and Sr compounds, respectively. The calculated electronic structures of these compounds show ionic bonding and no energy bandgap. The mechanical characteristics of compounds are also investigated as to meet the Born stability criterion, these compounds should be mechanically stable. The Cauchy pressure and Pugh criteria revealed that these materials have a brittle character and rather hard. In low energy range, all optical properties are found to be suitable as needed for storing the hydrogen. Furthermore, the gravimetric ratios suggested that all the compounds are suitable for hydrogen storage as a fuel for a longer time and may provide remarkable contributions in diversity of power and transportation applications.