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In this paper the changes of Mo species of Mo/Al2O3 and Mo/TiO2-Al2O3 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/Al2O3 is different.The bands of octahedral Mo species and their polymer at 215 and 971 cm(-1) disappeared first at 100 degrees C, and then crystalline MoO3 at 820 cm(-1) at below 300 degrees C in H-2. The bands of Al-2(MoO4)(3) phase at 377 and 1003 cm(-1) disappeared at 400 degrees C. Polymer of octahedral Mo species at 961 cm(-1) and crystalline MoO3 at 289, 666, 816 and 994 cm(-1) exist in Mo/TiO2-Al2O3 catalysts. The former was reduced at lower temperatures than the latter. (2) When H2S-H-2 flowed into sample cell at room temperature, the bands of oxidic Mo/Al2O3 disapeared, and simultaneously, the bands of MoS2 at 377, 401 cm(-1) and complicated molybdenum oxysulfide at 325, 348, 450, 540 cm(-1) emerged. After sulfiding at 400 degrees C, only MoS2 phase exists. For Mo/TiO2-Al2O3, the bands of Mo and TiO2 disappeared upon sulfiding of a sample at room temperature, and the bands of MoS2 at 375 and 398 cm(-1) emerged. This reveals that modification of the Al2O3 surface by TiO2 strongly enhances the sulfiding of Mo supported catalysts

A series of molybdena catalysts supported on titania-modified alumina carrier was characterized by X-ray diffraction (XRD), analytical electron microscopy (AEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction (TPR). The results show that the type of Mo6+ species depends upon the coverage of titania on alumina. The molybdenum atomic concentration was improved when most of the surface of alumina was occupied by titania. TPR profiles of molybdena/titania-alumina exhibit two peaks at 680-710 K and 1090-1100 K. The amount of hydrogen consumption in the TPR process increases with a rise in titania content, which suggests that titania promotes the reduction of molybdena to much lower valency. The XPS data is in agreement with the TPR results. The measurements of the activity of the catalyst in hydrodesulphurization (HDS) of thiophene and hydrogenation (HYD) of cyclohexene indicate that titania-modified alumina supports can improve the HDS primary activity of the catalyst.

IR-spectroscopy and chemisorption in accompanying with CO, NO, H-2, O-2 as probe molecules have been used to elucidate the function of cobalt and ruthenium in the reduced Co-Mo/Al2O3, Ru-Mo/Al2O3, Ru-Co-Mo/Al2O3 catalysts. It is found, the location of cobalt has a partial block effect on Mo sites in its low oxidation state for adsorbing CO, NO, H-2, O-2 probes on reduced Co-Mo/Al2O3 catalysts, the intensities of CO and NO bands on Co sites are increased and the NO bands are shifted to the higher freqency side by about 20 cm(-1) in comparing with that on Co/Al2O3 catalysts. In contrast to cobalt, uptake of CO, NO, H-2, O-2 probes are increased evidently on the Mo sitesin the coordination unsaturated state with the addition of ruthenium in the Ru-Mo/Al2O3 and Ru-Co-Mo/Al2O3 catalysts. It is suggested that ruthenium can promote the dissociation of hydrogen and the spilling of active hydrogen over Mo sites, which will be beneficial to the formation of more coordination unsaturated Mo sites.