Ni_2P/SiO_2 和Ni/SiO_2 催化剂甘油氢解反应性能比较:催化剂活性及产物选择性影响因素的探讨(英文)

采用浸渍法及程序升温还原法制备了Ni2P/SiO2和Ni/SiO2催化剂,利用N2吸附-脱附、X射线衍射、X射线荧光、CO化学吸附、氢气程序升温脱附及氨气程序升温脱附等手段对催化剂进行了表征并用于甘油氢解反应.结果表明,Ni2P/SiO2和Ni/SiO2具有相近的表面Ni密度,但前者表面酸中心和表面氢物种(包括吸附氢和溢流氢)密度明显更高,且在甘油氢解反应中的活性也更高,这与其酸性中心与金属中心之间的协同作用有关.Ni2P/SiO2催化剂上主要产物为1,2-丙二醇及1-丙醇,而Ni/SiO2催化剂上主要产物为1,2-丙二醇、乙二醇和乙醇.提高反应温度和H2压力不能促进Ni2P/SiO2上乙醇和乙二醇的生成,但促进了1,2-丙二醇进一步氢解转化为1-丙醇.由此可见,Ni2P/SiO2具有较强的C-O键断裂活性及较弱的C-C键断裂活性,这可能分别与其较多酸性中心和电子及几何结构性质密切相关.     

多中心d—pπ键与高氧化态钼簇合物的几何构型（I）“碎片结构”模型及分子轨

本文通过对不同构型的二核钼簇合物簇胳结构的分子轨道计算,揭示了Mo-B（T）原子间的多中心d-pπ键与该结构的稳定性及结构参数a,q和之间的内在联系，提出了2－6核高氧化态钼簇合物的簇胳由“碎片结构”组合而成的设想，该模型对以u2-S2为桥的三桥钼簇合物中的“共面－异面”规划的和簇胳为[Mo3S3O]^6 的钼簇中的反[常Mo-Mo键距级出合理解释，确认了桥原子对Mo-Mo键长和键强的决定作用。     

表面分散过程的分形研究

盐类和氧化物等活性组分在一定条件下,可在高比表面载体上自发分散。研究这些过程对多相催化剂、吸附剂的制备过程理解和控制无疑是重要的。这类分散过程已被系统地研究,并提出了单层分散模型,对CuCl_2/γ-Al_2O_3、HgCl_2/活性炭等多种体系,测定了单层分散阈值。表面化学习惯上理解为就是二维的化学。早在1931年Tayor就指出表面是不均匀的,但这种不均匀性是作为对理想二维表面的修正而引入的,如TLK模型。表面科学的这些基本概念其数学基础是欧基里德几何学,其物理背景是晶体结构,不规则性就是指晶体结     

Theoretical Study of Small Water Clusters of Sulfur Dioxide

The intermolecular clusters of sulfur dioxide with water, SO2(H2O)n (n = 2～5), are studied by using B3LYP density functional theory and MP2 ab initio methods along with the large basis sets (6-311++G(d,p) and aug-cc-pVDZ). The equilibrium geometries, intermolecular binding energies, and anharmonic frequencies of the clusters are calculated and compared with those of pure water clusters and available experiments. SO2 tends to form cyclic hydrogen-bonded complexes with two or three water molecules. In the larger clusters, however, water molecules begin to retain the structure of pure water clusters and segregate from SO2. Infrared absorption assignments for the small clusters are discussed to resolve a possible incorrect assignment in a recent spectroscopic experiment on the clusters.     

Theoretical Study on the Adsorption and Decomposition of Methanol over the Pt-Mo（111）/C Surface

The density functional theory(DFT) and self-consistent periodic calculation were used to investigate the methanol adsorption on the Pt-Mo(111)/C surface.The adsorption energies,equilibrium geometries and vibration frequencies of CH3OH on nine types of sites on the Pt-Mo(111)/C surface were predicted and the favorite adsorption site for methanol is the top-Pt site.Both sites of valence and conduction bands of doped system have been broadened,which are favorable for electrons to transfer to the cavity.The possible decomposition pathway was investigated with transition state searching and the calculation results indicate that the O-H bond is first broken,and then the methanol decomposes into methoxy.The activation barrier of O-H bond breaking with Pt-Mo catalyst is only 104.8 kJ mol-1,showing that carbon supported Pt-Mo alloys have promoted the decomposition of methanol.Comparing with the adsorption energies of CH3OH on the Pt(111)/C surface and that of CO,the adsorption energies of CO are higher,and Pt(111)/C is liable to be oxidized and loses the activity,which suggests that the catalyst Pt-Mo(111)/C is in favor of decomposing methanol and has better anti-poisoning ability than Pt(111)/C.     

Theoretical Study on Hydrogen Interaction between 5-Fluorouracil and Glycine

The geometries,electronic structure,IR spectrum and other properties of hydrogen interaction between 5-fluorouracil and glycine were studied at the B3LYP/6-31+G* level.Single point energy calculations were executed at the B3LYP/6-311++G** and B3LYP/aug-cc-pvdz levels,and natural bond orbital (NBO) analysis was carried out at the B3LYP/6-31+G* level.Finally,the hydrogen bonds were discussed via AIM electronic density topology analysis.     

Theoretical Studies on Structures and Electron Affinities of 5-and 6-Halouracils

The molecular structures and electron affinities of 5-and 6-halouracils(XU,X=F,Cl,Br) were determined by means of five different density functional methods. The basis set used in this work is of double-ζ plus polarization(DZP) quality with additional diffuse s-and p-type functions,denoted DZP++. The geometries were fully optimized with each density functional theory(DFT) method,and discussed. Three different types of the neutral-anion energy separations reported in this work are the adiabatic electron affin...     

1777年11月：利希滕贝格图形的发现

 被闪电击中的人在他们的皮肤上经常会产生红色、分枝状的图案,并常会持续好几天,这很可能是皮肤下易脆的微血管因电流冲击而破裂所致,是不规则分形的自然例子;俗语称之为“闪电花”,也被叫作“利希滕贝格图形”,以纪念18 世纪的物理学家利希滕贝格（Georg Christoph Lichtenberg）。     

定向断裂控制爆破下层理页岩的致裂机理

为探究定向断裂控制爆破下层理页岩的爆破致裂机理,采用切缝药包,对四种切缝角度下的页岩立方体试件进行爆破试验,采用数字图像相关技术（DIC）对页岩试件表面应变场的演化过程进行监测,分析了微裂纹孕育至宏观裂纹贯通的内在机理,并基于盒维数理论计算了不同切缝角度下页岩试件表面裂纹的分形维数,采用Matlab软件对爆后块度的筛分方法进行了编程分析,开发了全自动的粒径分析程序,实现了粒径圈定的可视化。试验结果表明：试件在不同比例爆距内的裂纹总密度与比例爆距之间存在负相关的幂函数关系,切缝方向与层理弱面的夹角对微观损伤区域出现的位置影响显著,当层理弱面与切缝方向平行时,损伤区域多集中于层理弱面处,对宏观裂纹的扩展路径影响显著,易于形成单一裂纹;层理弱面处的能量泄漏是造成页岩爆破破碎效果较差的重要因素,当切缝方向与层理弱面一致时,试件爆后的大块占比较高,爆后块度的分形维数平均值在各组间最低,仅为0.7843,而当切缝方向与层理面垂直时,试件的爆后块度分布较为均匀,爆后块度的分形维数平均值达到了2.5233,爆破破碎效果相对较好。