Pt/CexZr1-xO2 催化剂在含硫合成气中催化水煤气变换反应活性

 采用浸渍法制备了 Pt/Ce_xZr_1-xO₂ 催化剂, 通过 X 射线衍射和程序升温还原等方法对催化剂进行了表征, 并在固定床反应器中评价了催化剂在合成气和含硫合成气中的水煤气变换活性. 结果表明, 铈锆固溶体的氧化还原能力强于 CeO₂, Zr 的掺杂明显改善了 CeO₂ 的孔道结构, 其担载的 Pt 催化剂具有更高的金属分散度, 因而活性更高. 两种催化剂在含硫合成气中的催化活性较无硫合成气中的均有所降低, 且 H₂S 浓度越大, 催化剂活性下降越多, 但这种因吸附硫而引起的失活是可逆的, 即催化剂重新暴露在无 H₂S 重整气的还原性气氛下活性能基本恢复.     

HPLC-直链淀粉手性固定相拆分卡维地洛对映体

建立了卡维地洛对映体的高效液相色谱分析方法。使用Chiralpak AD-H手性色谱柱,考察了流动相中极性调节剂的种类和体积分数、流动相中二乙胺的体积分数、柱温以及流速对卡维地洛对映体拆分的影响。确定了最佳拆分条件:流动相为正己烷-异丙醇-二乙胺(体积比70∶30∶0.05);流速1.0 mL/min;检测波长243 nm;柱温30℃。卡维地洛与固定相相互作用的焓变差值Δ(ΔH0)和熵变差值Δ(ΔS0)分别为-505.6 J/mol和-1.055 J/(mol.K)。研究手性合成了(S)-卡维地洛,对映体过量值(e.e.)达99.0%以上。在优化实验条件下,通过考察峰面积的显著差异,得到卡维地洛对映体的出峰顺序为:先S体,后R体。所建立的方法简单快捷、重复性好,可用于卡维地洛的质量研究和控制。     

宽电压范围下阳极氧化制备TiO_2纳米管阵列及其热稳定性

采用电化学阳极氧化技术,以含有NH4F和H2O的甘油溶液为电解液,在宽氧化电压范围(20~100V)下于纯钛表面制备了结构高度有序的TiO2纳米管阵列。利用扫描电子显微镜(SEM)考察了阳极氧化工艺(氧化电压、NH4F浓度、环境温度、水分含量等因素)及退火处理对纳米管形貌的影响;采用X射线衍射分析(XRD)表征了不同氧化电压和退火前后TiO2纳米管阵列的物相;并从电流-时间曲线出发简要地分析了纳米管阵列的形成机理。结果表明,纳米管的内外径和管长随氧化电压的增大而增大;NH4F浓度和环境温度对纳米管形貌有一定的影响;水分含量的多寡决定了能否在高电压下自组装形成纳米管阵列;TiO2纳米管阵列具有良好的热稳定性,管状形貌可以保持到700℃;直接制备的TiO2纳米管阵列均为无定型结构,经450℃退火处理后,无定型的TiO2纳米管转变为锐钛矿相,而600℃退火处理后,部分锐钛矿相转变为金红石相。     

差分脉冲伏安法同时测定α-山竹黄酮和γ-山竹黄酮

研究了α-山竹黄酮和γ-山竹黄酮在玻璃碳电极上的电化学行为,研究了pH和静置时间等因素的影响,探讨了α-山竹黄酮和γ-山竹黄酮在玻璃碳电极上的氧化机理,建立了差分脉冲伏安法同时测定α-山竹黄酮和γ-山竹黄酮的方法。在pH 3.1的BR缓冲介质中,α-山竹黄酮在0.822 V产生灵敏的氧化峰,γ-山竹黄酮在0.426 V和0.700 V产生灵敏的氧化峰。对α-山竹黄酮,相应的氧化峰的峰高与浓度在5.00×10-6mol/L~2.00×10-4mol/L范围内呈良好的线性关系,线性相关系数为0.9950;对γ-山竹黄酮,其在0.426 V氧化峰的峰高与浓度在2.00×10-5mol/L~6.00×10-4mol/L浓度范围内呈良好的线性关系,线性相关系数为0.9904。该方法测量2.00×10-4mol/L的α-山竹黄酮和γ-山竹黄酮相对标准偏差分别为3.3%和4.1%(n=10)。     

3-[(1H-1,2,4-三唑-1-基)甲基]-1,1′-联萘酚的合成及晶体结构

成功地合成了化合物rac-3-[(1H-1,2,4-三唑-1-基)甲基]-1,1′-联萘酚,利用X射线单晶衍射确定了其空间结构;与此同时,利用1H NMR1、3C NMR和元素分析确认了所合成的中间体及目标产物的化学结构.结果表明,目标化合物晶体属于单斜晶系,P21/C空间群,晶胞参数a=1.141 39(10)nm,b=0.955 53(8)nm,c=1.688 16(14)nm,β=97.305(4)°,V=1.826 2(3)nm3,Z=4,Dc=1.336 g/cm3,F(000)=768,wR=0.105 9.目标分子通过分子间氢键作用相互堆积,形成空间三维结构.     

Molecular dynamics simulations of gas separations using faujasite-type zeolite membranes

Gas separations with faujasite zeolite membranes have been examined using the method of molecular dynamics. Two binary mixtures are investigated, oxygen/nitrogen and nitrogen/carbon dioxide. These mixtures have been found experimentally to exhibit contrasting behavior. In O(2)/N(2) mixtures the ideal selectivity (pure systems) is higher than the mixture selectivity, while in N(2)/CO(2) the mixture selectivity is higher than the ideal selectivity. One of the key goals of this work was to seek a fundamental molecular level understanding of such divergent behavior. Our simulation results (using previously developed intermolecular models for both the gases and zeolites investigated) were found to replicate this experimental behavior. By examining the loading of the membranes and the diffusion rates inside the zeolites, we have been able to explain such contrasting behavior of O(2)/N(2) and N(2)/CO(2) mixtures. In the case of O(2)/N(2) mixtures, the adsorption and loading of both O(2) and N(2) in the membrane are quite competitive, and thus the drop in the selectivity in the mixture is primarily the result of oxygen slowing the diffusion of nitrogen and nitrogen somewhat increasing the diffusion of oxygen when they pass through the zeolite pores. In N(2)/CO(2) systems, CO(2) is rather selectively adsorbed and loaded in the zeolite, leaving very little room for N(2) adsorption. Thus although N(2) continues to have a higher diffusion rate than CO(2) even in the mixture, there are so few N(2) molecules in the zeolite in mixtures that the selectivity of the mixture increases significantly compared to the ideal (pure system) values. We have also compared simulation results with hydrodynamic theories that classify the permeance of membranes to be either due to surface diffusion, viscous flow, or Knudsen diffusion. Our results show surface diffusion to be the dominant mode, except in the case of N(2)/CO(2) binary mixtures where Knudsen diffusion also makes a contribution to N(2) transport.     

Crystalline Hetero‐Stereocomplexed Polycarbonates Produced from Amorphous Opposite Enantiomers Having Different Chemical Structures

Stereocomplexation is the stereoselective interaction between two opposite enantiomeric polymers through an interlocked orderly assembly. Most studies focus on the stereocomplex formation from the crystalline opposite enantiomers having the identical structure; nevertheless, rare examples were reported regarding the crystalline stereocomplexes from enantiomeric polymers having different chemical structures. Herein we show a strategy for polymer orderly assembly through the formation of crystalline hetero‐stereocomplexed polymeric materials by the cocrystallization of amorphous isotactic polycarbonates with different chemical structures and opposite configurations. The behaviors in the crystalline state are significantly different from that of the component enantiomeric polymers or their homo‐stereocomplexes. This study is expected to open up a new way to prepare various semicrystalline materials having a wide variety of physical properties and degradability.     

Clicked Isoreticular Metal–Organic Frameworks and Their High Performance in the Selective Capture and Separation of Large Organic Molecules

Three highly porous metal–organic frameworks (MOFs) with a uniform rht‐type topological network but hierarchical pores were successfully constructed by the assembly of triazole‐containing dendritic hexacarboxylate ligands with Zn^II ions. These transparent MOF crystals present gradually increasing pore sizes upon extension of the length of the organic backbone, as clearly identified by structural analysis and gas‐adsorption experiments. The inherent accessibility of the pores to large molecules endows these materials with unique properties for the uptake of large guest molecules. The visible selective adsorption of dye molecules makes these MOFs highly promising porous materials for pore‐size‐dependent large‐molecule capture and separation.     

Liquid‐Crystalline Mesogens Based on Cyclo[6]aramides: Distinctive Phase Transitions in Response to Macrocyclic Host–Guest Interactions

Producing macrocyclic mesogens that are responsive to guest encapsulation presents a significant challenge. Cyclo[6]aramides, a type of macrocycle with a hydrogen‐bond‐constrained backbone, exhibit thermotropic lamellar, discotic nematic, hexagonal, and rectangular columnar mesophases over a considerably wide temperature range, including at room temperature. Additionally, cyclo[6]aramides show unusual mesophase transitions from lamellar to hexagonal columnar phase mediated by macrocyclic host–guest (H–G) interactions between the macrocycles and alkylammonium salts. The phase transition, triggered by an organic guest engaging in H–G interactions with a macrocyclic cavity, provides a novel strategy for manipulating the properties of liquid‐crystalline materials. The crystal structure of a homologous cyclo[6]aramide reveals a disk‐shaped, near‐planar molecular backbone that facilitates intermolecular π–π stacking and leads to columnar assembly.     

Wrinkled Graphene Monoliths as Superabsorbing Building Blocks for Superhydrophobic and Superhydrophilic Surfaces

Superhydrophobic and superhydrophilic surfaces are of great interest because of a large range of applications, for example, as antifogging and self‐cleaning coatings, as antibiofouling paints for boats, in metal refining, and for water–oil separation. An aqueous ink based on three‐dimensional graphene monoliths (Gr) can be used for constructing both superhydrophobic and superhydrophilic surfaces on arbitrary substrates with different surficial structures from the meso‐ to the macroscale. The surface wettability of a Gr‐coated surface mainly depends on which additional layers (air for a superhydrophobic surface and water for a superhydrophilic surface) are adsorbed on the surface of the graphene sheets. Switching a Gr‐coated surface between being superhydrophobic and superhydrophilic can thus be easily achieved by drying and prewetting with ethanol. The Gr‐based superhydrophobic membranes or films should have great potential as efficient separators for fast and gravity‐driven oil–water separation.