Abstract:

In this paper the changes of Mo species of Mo/Al_2O_3 and Mo/TiO_2-Al_2O_3 catalysts in reducing and sulfiding process have been studied by in situ LR spectroscopic technique. The results show: (1) The reducibility of various Mo species in Mo/Al_2O_3 is different.The bands of octahedral Mo species and their polymer at 215 and 971 cm~(-1) disappeared first at 100 ℃, and then crystalline MoO_3 at 820 cm~(-1) at below 300 ℃ in H_2. The bands of Al_2(MoO_4)_3 phase at 377 and 1003 cm~(-1) disappeared at 400 ℃. Polymer of octahedral Mo species at 961 cm~(-1) and crystalline MoO_3 at 289, 666, 816 and 994 cm~(-1) exist in Mo/TiO_2-Al_2O_3 catalysts. The former was reduced at lower temperatures than the latter. (2) When H_2S-H_2 flowed into sample cell at room temperature, the bands of oxidic Mo/Al_2O_3 disapeared, and simultaneously, the bands of MoS_2 at 377, 401 cm~(-1) and complicated molybdenum oxysulfide at 325, 348, 450, 540 cm~(-1) emerged. After sulfiding at 400 ℃, only MoS_2 phase exists. For Mo/TiO_2-Al_2O_3, the bands of Mo and TiO_2 disappeared upon sulfiding of a sample at room temperature, and the bands of MoS_2 at 375 and 398 cm~(-1) emerged. This reveals that modification of the Al_2O_3 surface by TiO_2 strongly enhances the sulfiding of Mo supported catalysts.

Key words: In situ LRS, Reduction, Sulfidation, Mo/Al2O3, Mo/TiO2-Al2O3