甲烷化反应过程中硫化的钼催化剂的拉曼光谱研究

本文研究了以γ-Al_2O_3、ZrO_2、CeO_2及La_2O_3为载体的硫化态钼催化剂在甲烷化反应过程中的激光拉曼光谱,发现在反应初期,催化剂表面氧硫钼结构变化较大,其活性下降也较快.在反应温度下,催化剂表面上的-S-键松动,部分硫原子升华,并发生一系列氧硫交换,形成体相MoS_2.甲烷化催化剂活性达到稳定后,则催化剂表面上的主要变化是MoS_2.晶粒不断长大.由于载体效应的影响.各个催化剂上表面结构的不同,与其达到活性稳定的时间有着直接的联系.另外,在反应过程中,催化剂表面上均无积碳形成.提出了硫化态钼催化剂在甲烷化反应过程中的表面结构变化模型.     

Nonlinear Optical Properties and Ultrafast Dynamics of Undoped and Doped Bulk SiC

Ultrafast third-order nonlinear optical response of bulk 6H-SiC undoped and doped with different nitrogen concentrations are investigated utilizing femtosecond Z-scan and optical Kerr effect （OKE） techniques at the wavelength of 800hm. The Z-scan measurement shows that the third-order nonlinear optical susceptibilities of the doped samples are improved in comparison to the intrinsic sample. The OKE results additionally reveal that the instantaneous nonlinear optical response of the samples can be ascribed to the distortion of the electron cloud. The ultrafast transient spectroscopic measurements with the one-color and two-color pump-probe techniques demonstrate that the ultrafast recovery process in subpicosecond domain is induced by two-photon absorption process, while the slow relaxation component reflects the carrier dynamics of the excited electrons.