The Structure Property And In-Situ Characterization Of Hydrodesulfurization Catalyst

The production of clean gasoline has to face enormous challenges now, then the basic research about hydrodesulfurization catalyst becomes more necessary. In-situ technology, which is a powerful tool for the catalyst studying, is often used for researching the changes of the structure of catalyst when it’s on work, by this way some important information can be obtained such as active phase structure, adsorption mode, reaction intermediates and reaction mechanism and so on.A series of industrial hydrodesulfurization catalysts are produced in this experiment by the equal volume impregnation method, which are Co/y-A12O3、Mo/γ-Al2O3、MOCO/γ-AI2O3、CoMo/γ-AI2O3. Then the catalysts are sulfided, at last oxydic states and sulfided catalysts are characterized by BET, XRD, FTIR, Laser Raman, by that way the structure of catalyst surface can be obtained.The results show that:it is very easy to form Co3O4on the surface of Co/γ-A12O3. For MO/γ-AI2O3, there are tetrahedral Mo species, octahedral Mo species, polymer Mo species and crystalline MoO3and so on. When supported by Co, CoMoO4appears and the MoO3crystal decreases, which indicates that Co can promote the dispersion of the Mo on the surface of Y-A12O3.In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS) results show that:thiophene can be adsorbed on unsaturated coordination Mo atoms. Besides, S atom and Mo can form S-M bond, then electrons flow to Mo from S. which can destroy the aromaticity of thiophene and weaken the C-S bond to achieve the purpose of desulfurization. Obviously, with the adding of Co, the distribution of Mo is improved and more active phase is formed. On the other hand, the electron-deficient of Mo will increase and S-M bond will enhance when Co is added, which make it much easier for the removal of S and improve the reactivity.Deactivated catalysts can easily be activated to form MoS2under hydrogen atmosphere. Under reaction conditions, only MoS2being found is a secondary evidence that MoS2is the active phase of hydridesulfurization. For Co/λ-Al2O3、Mo/λ-Al2O3、MoCo/λ-Al2O3, the reduction temperatures are not the same and the reduction temperatures of different vibration modes are diverse from each other, either.In-situ XRD experiments confirm:in the heating process of sulfided catalyst, phase transition occurs at400℃and the catalyst forms MoO3phase, then the sulfided catalyst will transform to oxidation state because S atoms is replaced by O atoms when temperature is continuing to heat up.