CoMo/TiO_2和CoMo/γ-Al_2O_3催化剂硫化行为的研究

STUDIES ON SULFIDATION OF CoMo/TiO_2 AND CoMo/Al_2O_3 CATALYSTS

运用程序升温硫化和原位激光拉曼光谱方法研究了CoMo/Al_2O_3和CoMo/TiO_2催化剂的硫化行为。结果表明,两种载体上Co和Mo氧化态物种的硫化均通过O-S交换,Mo—S或Co—S键断裂,元素S被H_2还原和高温下进一步深度硫化等多步骤完成。由于TiO_2载体上Mo物种主要以八面体配位Mo—O—Mo形式存在以及TiO_2载体参与硫化过程,CoMo/TiO_2比CoMo/Al_2O_3容易硫化。

The sulfidation of CoMo/TiO_2 and CoMo/Al_2O_3 catalysts was studied by means of temperature programmed sulfiding (TPS) and in situ laser raman spectroscopy (LRS). The results showed that CoMo supported on TiO_2 and Al_2O_3 are sulfided to MoS_2 and Co_9S_8 by a multistep process. First, oxidie Co and CoMo species are partially sulfided by O-S exchange at low temperature forming Mo and CoMo oxysulfide. Then, the Mo—S or Co—S bond reptures in the presence of H_2 to produce H_2S. Finally, the deep sulfiding of Mo or CoMo oxysulfide occurs forming crystalline sulfides of Mo and Co. It has been found that the sulfidation of CoMo/TiO_2 catalysts takes place at much lower temperature as compared with CoMo/Al_2O_3 catalyst. The reasons are that the main Mo species on TiO_2 support exist in octahedral Mo—O—Mo bridge structure, which are easilly to be sulfided, while the presence of tetrahedral Mo species on Al_2O_3 support needs higher temperature for sulfiding. Another difference between CoMo/TiO_2 and CoMo/Al_2O_3 is that the oxygen in TiO_2 support can be exchanged with S in H_2S, thus promoting the sulfiding of Co and Mo species, while Al_2O_3 does not.