Abstract:  The TiO₂-Al₂O₃ composite oxide was synthesized by the hydrothermal method. The effects of hydrothermal temperature, reactant concentration, average molecular mass of polyethylene glycol, and polyethylene glycol concentration on the structural and textural properties of TiO₂-Al₂O₃ composite oxide were studied. The composite oxide and NiMoP/TiO₂-Al₂O₃ catalyst were characterized by powder X-ray diffraction, N₂ adsorption-desorption, scanning electron microscopy (SEM), thermogravimetric and differential thermal analysis (TG-DTA), NH₃ temperature-programmed desorption (NH₃-TPD), pyridine adsorption in situ infrared spectroscopy (Py-FTIR), and H₂ temperature-programmed reduction (H₂-TPR). The catalytic performance of the catalyst for hydrodesulfurization of fluid catalytic cracking (FCC) diesel was evaluated in a fixed-bed reactor with medium pressure. The results show that both specific surface area and pore volume of the TiO₂-Al₂O₃ composite oxide increased with increasing hydrothermal temperature, reactant concentration, average molecular mass of polyethylene glycol, and polyethylene glycol concentration. Under the optimum conditions, the specific surface area and pore volume of the TiO₂-Al₂O₃ composite oxide could reach up to 266 m²/g and 0.58 cm³/g, respectively. The specific surface area of NiMoP/TiO₂-Al₂O₃ catalyst also reached as high as 175 m²/g. The results of NH₃-TPD and Py-FTIR show that NiMoP/TiO₂-Al₂O₃ catalyst has a weak acidity wherein Lewis acid is dominative. The NiMoP/TiO₂-Al₂O₃ catalyst has higher desulfurization activity due to the existence of TiO₂, which can decrease the strong interaction between the active phase and the support. Hydrodesulfurization activity for FCC diesel over NiMoP/TiO₂-Al₂O₃ catalyst is thus 5.4% higher than that on the NiMoP/Al₂O₃ catalyst.

Key words: titania, alumina, composite oxide, hydrothermal synthesis, polyethylene glycol, fluid catalytic cracking diesel, hydrodesulfurization