碱金属助剂对 Au-Pt/CeO2 催化剂催化水煤气变换反应活性的影响

 制备了碱金属 M (M = Na, K, Rb 和 Cs) 掺杂的 Au-Pt/CeO2 催化剂, 考察了其催化水煤气变换反应的活性, 并采用 X 射线衍射、H2 程序升温还原、紫外-可见漫反射光谱和 X 射线光电子能谱技术研究了 K 助剂对 Au-Pt/CeO2 催化剂结构和表面性质的影响. 结果表明, 添加少量电负性较低的 K 虽然使 Pt 的还原变得困难, 但有利于 Au 金属态的稳定, 并使催化剂表面 Ce3+ 富集而产生氧空位, 显著提高了 Au-Pt/CeO2 催化剂活性. 当 K 负载量为 0.025%, 反应温度 250 oC 时, CO 转化率可达 95%.     

关于度量及纲函数的Hausdorff测度的两个反例

本文研究了度量空间中Hausdorff测度与度量及纲函数的关系.利用拓扑学及Hausdorff测度论中一些性质,构造了两反例来说明存在不等价纲函数g,h和某一紧度量空间(ρ,X),使得Hρ,g与Hρ,h对此紧度量空间等价等问题.这些反例有助于从另一个角度理解文胜友、文志英[4]中主要结果.     

煤溶剂萃取物组成的气相色谱/质谱分析

分别采用丙酮、N,N-二甲基甲酰胺、乙醇胺、乙二胺对陕西某一地区煤进行了索氏萃取和搅拌萃取,其中以乙二胺为溶剂,采用简单搅拌萃取的萃取率最高,可达17.1%。建立了气相色谱/质谱法(GC/MS)测定乙二胺和乙醇胺萃取物的分析方法,结果表明:乙二胺萃取物中可检测出53种化合物,主要为芳香烃、脂肪烃、含氮及含氧化合物四类组分。含氮化合物的成分含量最高,气相色谱分析其面积归一化相对含量为75.64%。检测出的乙醇胺萃取物种类较少,与乙二胺萃取物的组成成分也有差别。并对影响萃取率和萃取物组成成分的因素进行了分析。     

Loss of cold atoms due to collisions with residual gases in free flight in a magneto-optical trap

The loss rate of cold atoms in a trap due to residual gas collisions differs from that in a free state after the cold atoms are released from the trap. In this paper, the loss rate in a cold rubidium-87 atom cloud was measured in a magneto-optical trap(MOT) and during its free flight. The residual gas pressure was analyzed by a residual gas analyzer, and the pressure distribution in a vacuum chamber was numerically calculated by the angular coefficient method. The decay factor, which describes the decay behavior of cold atoms due to residual gas collisions during a free flight, was calculated. It was found that the decay factor agrees well with theoretical predictions under various vacuum conditions.