Characterization study of NiMo/SiO2-Al2O3 spent hydroprocessing catalysts for heavy oils

• NiMo/SiO2-Al2O3 spent catalysts characterized by several techniques.
• Decreasing of acid catalytic sites confirmed by cumene hydrocracking.
• Activity of acidic catalysts affected by carbon and metal deposition.

NiMo/SiO2-Al2O3 spent catalysts were obtained after the hydroprocessing of Maya crude oil in a fixed-bed up-flow reactor. The textural properties, metal content, carbon deposition and sulfide phase of spent catalysts were studied and compared with those of fresh catalysts. Scanning electron microscopy was used to study the deposit of nickel and vanadium, and the total metal content was determined by atomic absorption. The sulfide phase was analyzed with the use of infrared spectroscopy technique. Moreover, the catalytic activity of spent catalysts was evaluated with cumene hydrocracking and compared with the catalytic activities of fresh catalysts. The characterization results show that the silica-alumina NiMo catalysts are more sensitive to metal deposition than carbon deposition because of their porous structure which provokes pore mouth plugging and the decrease of the NiMoS active sulfide phase. The results show that optimizing the catalyst resistance to deactivation requires a trade-off between the support acidity and macro-mesoporosity.