Synthesis and hydrolytic degradation of poly (glycerol succinate) based polyesters

The limited availability of petroleum resources motivates the research towards value-added products production from bio-resources. This study reports the synthesis of glycerol and succinic acid-based polyesters and their detailed characterization. The modification of poly (glycerol succinate) was done by using other diacids like glutaric acid, adipic acid, azelaic acid, sebacic acid, and dodecanedioic acid. The sysnthesized polyesters were characterized using various techniques such as thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), Nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The addition of different dicarboxylic acids to poly (glycerol succinate) based co-polyesters increased the thermal stability of poly (Glycerol succinate). Glass transition temperatures were obtained in the range of ?17.2 to ?22.5 °C and it increased with chain length. The progress of reaction was monitored by determining acid number, ester number, and degree of esterification. The hydrolytic degradation of polyesters was carried out in acidic and basic medium. The polyesters was found to degrade under basic conditions whereas no weight loss of poly (glycerol succinate) was found under acidic conditions. Particularly, about 40% of poly (glycerol succinate) was degraded within 24 h under basic conditions (pH = 12). The analysis of morphology of polyesters during degradation showed that the increase in hydrolysis time increased the heterogeneity in polyester matrix.     

Direct Detection of FeVI Water Oxidation Intermediates in an Aqueous Solution

In situ detection of highly-oxidized metal intermediates is the key to identifying the active center of an oxygen evolution reaction (OER) catalyst, but it remains challenging for NiFe-based catalysts in an aqueous solution under working conditions. Here, by utilizing the dynamic stability of the Fe^VIO₄²⁻ intermediates in a self-healing water oxidation cycle of NiFe-based catalyst, the highly-oxidized Fe^VI intermediates leached into the electrolyte are directly detected by simple spectroelectrochemistry. Our results provide direct evidence that Fe is the active center in NiFe-based OER catalysts. Furthermore, it is revealed that the incorporation of Co into NiFe-based catalyst facilitates the formation of Fe^VI active species, thus enhancing the OER activity of NiCoFe-based catalyst. The insights into the mechanisms for the sustainable generation of Fe^VI active species in these NiFe-based catalysts lay the foundation for the design of more efficient and stable OER catalysts.     

Brnsted-Evans-Polanyi关系筛选最优催化剂

基于反应活化能和反应热间存在的线性Brnsted-Evans-Polanyi (BEP)关系,对双原子分子、三原子分子和多原子分子等无机小分子的活化和有机分子键的断裂等进行概要的描述. BEP关系能够帮助人们定量地理解催化活性的"火山图形",结合各个反应的特性寻找最优吸附能的范围,同时也为研究反应进行的优先顺序,反应速率快慢提供了一个方法 .随着计算能力的不断提高,相关理论的不断发展,寻找和筛选高效廉价的催化剂会越来越方便、快速、精确. BEP关系简单、快速、有选择性的特点使人们能够结合各种情况选择非稀有、环境友好、便宜、催化效率高的多相催化剂.     

Surfactant-assisted synthesis of defective zirconia mesophases and Pd/ZrO2: Crystalline structure and catalytic properties

Mesoporous zirconia nanophases with structural defects were synthesized by using a surfactant-templated method. Physicochemical properties and crystalline structures of the zirconia nanophases were studied by means of thermogravimetric analysis (TGA), N₂ physosorption isotherm and in situ Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques. The resultant materials show typical mesoporous features which vary with calcination temperature. The cationic surfactant in the network of the solids induces structural deformation and defect creation. The zirconia consists of monoclinic and tetragonal nanophases which contains many structural defects, and its crystalline structure shows microstrain. Both, concentration of lattice defects and degree of the crystal microstrain, decrease as the calcination temperature is increased. When CO is adsorbed on the surface of Pd/ZrO₂, linear bonds of CO–Pd⁰, CO–Pd^δ+ and CO–Zr⁴⁺ are formed, accompanying with CO₂ production. Catalytic evaluation shows that the Pd/ZrO₂ catalyst is very active for CO oxidation and NO reduction. In the case of oxygen absence from reaction mixture, high selectivity to N₂ is achieved without any NO₂ formation. In the oxygen rich condition, CO conversion is enhanced but less than 19% NO₂ is produced. N₂O is formed only in the reducing condition and its selectivity is sensitive to reaction temperature. The possible mechanisms of NO + CO and NO + CO + O₂ reactions over Pd/ZrO₂ catalyst related to reactant dissociation on the Pd metals and to defective structure of the nanozirconia support are discussed.     

Kinetic study on catalytic gasification of a modified sludge fuel

A new type of mixture fuel, sludge-oil-coal agglomerate (SOCA), was catalytically gasified with steam in a thermobalance reactor under atmospheric pressure. All the four catalysts studied (KeCO3, CaO, NiO and Fe2O3) were found capable of enhancing the steam gasification rate and significantly increasing the conversion of carbon. The ranking of catalytic activity was found to be K2CO3 >> CaO > NiO > Fe2O3. A modified volumetric-reaction model in the literature was used to describe the conversion behavior of the steam gasification studied by evaluating the kinetic parameters. Expressions of the apparent gasification rates for SOCA were presented for the design of catalytic gasification processes.     

Polymerization Kinetics of Propylene with the MgCl_2-Supported Ziegler-Natta Catalysts——Active Centers with Different Tacticity and Fragmentation of the Catalyst

The catalytic activity and stereospecificity of olefin polymerization by using heterogeneous TiCl_4/MgCl_2 Ziegler-Natta(Z-N) catalysts are determined by the structure and nature of active centers, which are mysterious and fairly controversial. In this work, the propylene polymerization kinetics under different polymerization temperatures by using Z-N catalysts were investigated through monitoring the concentration of active centers [C*] with different tacticity. SEM was applied to characterize the catalyst morphologies and growing polypropylene(PP) particles. The lamellar thickness and crystallizability of PP obtained under different polymerization conditions were analyzed by DSC and SAXS. The PP fractions and active centers with different tacticity were obtained with solvent extraction fractionation method. The catalytic activity, active centers with different tacticity and propagation rate constant k_p, fragmentation of the catalyst, crystalline structure of PP are correlated with temperature and time for propylene polymerizations. The polymerization temperature and time show complex influences on the propylene polymerization. The higher polymerization temperature(60 ℃) resulted higher activity, k_p and lower [C*], and the isotactic active centers C_i* as the majority ones producing the highest isotactic polypropylene(iPP) components showed much higher k_p when compared with the active centers with lower stereoselectivity. Appropriate polymerization time provided full fragmentation of the catalyst and minimum diffusion limitation. This work aims to elucidate the formation and evolution of active centers with different tacticity under different polymerization temperature and time and its relations with the fragmentation of the PP/catalyst particles, and provide the solutions to the improvement of catalyst activity and isotacticity of PP.     

Bimetal-organic frameworks derived Co/N-doped carbons for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries have received extensive attention due to their high theoretical specific energy density. However, the utilization of sulfur is seriously reduced by the shuttle effect of lithium polysulfides and the low conductivity of sulfur and lithium sulfide (Li₂S). Herein, we introduced bimetal-organic frameworks (Co/Zn-ZIF) derived cobalt and nitrogen-doped carbons (Co/N-C) into Li-S batteries through host design and separator modification. The Co/N-C in Li-S batteries effectively limits the shuttle effect through simultaneously serving as polysulfide traps and chemical catalyst. As a result, the Li-S batteries deliver a high reversible capacity of 1614.5 mAh/g and superior long-term cycling stability with a negligible capacity decay of only 0.04% per cycle after 1000 cycles. Furthermore, they have a high area capacity of 5.5 mAh/cm².     

Neuronal nicotinic receptor agonists: a multi-approach development of the pharmacophore

Based on the results obtained with different automated computational approaches as applied to the study of eleven high-affinity agonists of the neuronal nicotine acetylcholine receptor (nAChR), belonging to different chemical classes, new relevant features were detected which complement the existing pharmacophores. Convergent results from DISCO (Distance Comparison), QXP (Quick Explore), Catalyst/HipHop, and MIPSIM (Molecular Interaction Potential Similarity) allowed us to identify and locate, in a well defined spatial arrangement, three geometrically independent key structural features: (i) a positively charged nitrogen atom for ionic or hydrogen bond interactions, (ii) a lone pair of the pyridine nitrogen or a specific lone pair of a carbonyl oxygen, as a hydrogen bond acceptor, and (iii) a centre of a hydrophobic area generally occupied by aliphatic cycles. The pharmacophore presented herein, along with predictive 2D and 3D QSAR models recently developed in our group, could represent valuable computational tools for the design of new nAChR agonists having therapeutical potential.     

Preparations of Pure Alkaline Earth Molybdate Phases from Single Molecular Precursors

IntroductionMetal molybdates are extensively used as cata-lysts for the partial oxidation and dehydrogenationreactions of hydrocarbons.Particularly,magne-sium molybdates have been studied for being ap-plied in the oxidative dehydrogenation of propaneand butane[1_ 5] .Because of the limited availabilityof well- characterized molybdenum compounds,thepreparations of such Mo- based catalysts in the purephase are not straightforward.Therefore,new re-searches on the suitable Mo precursors seem to b…     

Pt/HM、Pd/HM催化剂上CO氧化反应活性和动力学研究

研究了Pt/HM、Pd/HM催化剂上CO氧化反应的活性,求出了各种催化剂的CO氧化反应动力学方程。考察了不同气氛下CO氧化活性的演变规律和V⁴⁺、Co²⁺离子对Pt、Pd的助催化作用,并用催化剂集团结构适应模型对以上结果作出了解释。