介孔SiO2负载的纳米金及其催化应用

金（Au）的催化作用已成为催化领域的前沿研究课题。本文综述了近年来采用不同方法制备介孔二氧化硅(MCM-41, MCM-48, SBA-15)负载的纳米Au催化剂以及在CO低温氧化、环己烯加氢和环己烷氧化等反应中的催化作用。讨论了影响纳米Au催化剂活性的相关因素, 包括载体的种类、表面性质、Au纳米颗粒的尺寸、分散度以及稳定性等。最后对各种制备纳米Au的方法进行了总结。     

CO2加氢合成甲醇催化反应中CO的作用

研究了铜基催化剂上CO₂加氢合成甲醇反应中掺人CO的作用,结果表明,在原料中添加少量CO,甲醇的选择性提高38%,收率提高25%;TPD-MS和TPSR-MS结果表明,CO能抑制催化剂表面起逆水汽变换作用的活性位对CO₂的吸附,从而提高了CO₂加氢合成甲醇的选抒性.     

Review of magnetocaloric effect in perovskite-type oxides

We survey the magnetocaloric effect in perovskite-type oxides (including doped ABO 3-type manganese oxides, A3B2O7-type two-layered perovskite oxides, and A2B'B'O6-type ordered double-perovskite oxides). Magnetic entropy changes larger than those of gadolinium can be observed in polycrystalline La1-xCaxMnO3 and alkali-metal (Na or K) doped La0.8Ca0.2MnO3 perovskite-type manganese oxides. The large magnetic entropy change produced by an abrupt reduction of magnetization is attributed to the anomalous thermal expansion at the Curie temperature. Considerable magnetic entropy changes can also be observed in two-layered perovskites La1.6Ca1.4Mn2O7 and La2.5-xK0.5+xMn2O7+δ (0 x 0.5), and double-perovskite Ba2Fe1+xMo1-xO6 (0 ≤ x ≤ 0.3) near their respective Curie temperatures. Compared with rare earth metals and their alloys, the perovskite-type oxides are lower in cost, and they exhibit higher chemical stability and higher electrical resistivity, which together favor lower eddy-current heating. They are potential magnetic refrigerants at high temperatures, especially near room temperature.     

原子团簇P10模型的理论计算

用分子图形学方法设计出２６种Ｐ１２模型,并对其进行了分子力学、ＰＭ３半经验量子化学和Ｈａｒｔｒｅｅ－Ｆｏｃｋ从头算优化。在Ｐ１０原子团簇模型设计中,磷原子采用一、二、三或四配位。大部分Ｐ１０的模型是在Ｐ９＾＋和Ｐ８的模型上分别增加、,２个原子生成的。这些模型包括１５种在势能面上局域极小点和１１种鞍点（或过流态）。从模型优化后的能量比较可知,２个四面体Ｐ４与１个Ｐ２通过４个单键连接的桥式结构最稳定。