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After the catalyst has been dried with nitrogen, hydrogen is introduced to displace the nitrogen; once this is done, the pressure is increased to the operating pressure. The cycle compressor is started, and the heating furnace is re-ignited to maintain the reaction temperature at 150°C. Then, wet sulfidation of the catalyst is carried out following these steps: hydrogen is circulated in full volume, and the temperature at the reactor inlet is kept between 150°C and 160°C. The sulfurizing oil is fed into the reaction system at a volumetric flow rate that does not exceed the design value. The initial amount of sulfurizing agent to be used is determined based on factors such as the flow rate of circulating hydrogen, the amount of catalyst used, the theoretical amount of sulfur required for pre-sulfidization of the catalyst, and the sulfidation time. After the sulfurizing agent is added, the catalyst is kept at a constant temperature of 150°C for 2 hours. Once the temperature of the catalyst bed in the reactor stabilizes, the temperature at the reactor inlet is increased slowly. The temperature at any point in the catalyst bed must not exceed 230°C until H2S is detected in the circulating hydrogen. When the concentration of H2S in the circulating hydrogen exceeds 0.1 v%, the temperature at the reactor inlet is adjusted so that the temperature of the catalyst bed remains around 230°C. Sulfidation continues at this constant temperature for a certain period of time (usually no less than 8 hours), during which the concentration of H2S in the circulating hydrogen should remain between 0.1% and 0.6% v%. After the sulfidation at 230°C is complete, the amount of sulfurizing agent added is adjusted so that the concentration of H2S in the circulating hydrogen reaches 0.5% to 1.0% v%. Meanwhile, the temperature at the reactor inlet is increased to 290°C at an appropriate rate. When the reactor inlet temperature reaches 290°C, sulfidation is carried out at a constant temperature for 8 hours. After this period of constant-temperature sulfidation at 290°C, the H2S concentration in the circulating hydrogen is adjusted to 1.0–2.0% (v), and the reactor inlet temperature is increased. Once the temperature of the catalyst bed rises to around 340°C, sulfidation continues at a constant temperature for another 4–8 hours. Sulfidation of the catalyst is considered complete when the following conditions are met: the amount of sulfiding agent used meets the theoretical requirement for sulfidation; there is almost no increase in the temperature of the catalyst bed; and there is no significant increase in the amount of water produced. After sulfidation is complete, the reactor inlet temperature is reduced to 250–280°C, and straight-run light diesel is used to stabilize the initial activity of the catalyst, usually for 48 hours. Afterwards, the designed feed is introduced, and operations are adjusted according to the predetermined parameters before the system resumes normal operation. Points to note during catalyst sulfidation: if the injection of the sulfiding agent has to be interrupted for some reason, the temperature of the catalyst bed should be reduced to below 230°C. If the interruption in sulfiding agent injection lasts for an extended period and the H2S concentration in the circulating hydrogen cannot be maintained above 0.1% (v), then the temperature of the catalyst bed should be reduced to 175°C. Since oil has a higher heat capacity than hydrogen, the heat transfer conditions during wet sulfidation are favorable. Therefore, hydrogenation refining catalysts using alumina or silicon-containing alumina as carriers, as well as hydrocracking catalysts based on amorphous silica-alumina or those containing a small amount of molecular sieves, can all be subjected to wet sulfidization. Hydrocracking catalysts containing molecular sieves – especially those with a high content of such sieves – exhibit much higher cracking activity than amorphous silica-alumina catalysts; they are particularly sensitive to reaction temperature, especially during the initial stages of operation. If wet sulfidization is used and sulfidization takes place at temperatures above 320°C, the cracking of the sulfided oil can lead to overheating of the catalyst bed, and it can also accelerate catalyst coking, affecting the stability of the catalyst’s activity