Lacunary Keggin Polyoxotungstate as Reaction-controlled Phase-transfer Catalyst for Catalytic Epoxidation of Olefins

A new reaction-controlled phase-transfer catalyst system, lacunary Keggin polyoxotungstate [C7H7N(CH3)3]9PW9O34 has been synthesized and used for catalytic epoxidation of olefins with H2O2 as the oxidant. Infrared spectra were used to analyze the behavior of the phase transfer of catalyst. In this system, the catalyst not only can act as homogeneous catalyst but also as heterogeneous catalyst to be easily filtered and reused. The epoxidarion reaction is clean and exhibits high conversion and selectivity as well as excellent catalyst stability.     

等离子体中涡旋光束自聚焦与成丝现象的模拟研究

涡旋光束在低密度等离子体传输过程中出现的非线性物理效应与光子携带的轨道角动量(拓扑荷)存在密切关联.基于亥姆霍兹方程理论获得描述涡旋光束传输的旁轴近似方程,解析求出涡旋光束在低密度等离子体中传输的自聚焦临界功率表达式.利用分步傅里叶数值方法,针对不同参数条件下涡旋光束的自聚焦和成丝现象进行了模拟分析.研究结果表明,涡旋光束的拓扑荷数决定了自聚焦临界功率大小.涡旋光束发生成丝不稳定性现象的功率阈值和最大成丝数目与拓扑荷数存在密切关联.