Pre-sulfurization of CoMo series catalysts

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During the presulfidization of CoMo catalysts, it is necessary to ensure that H2S penetrates the catalyst bed before raising the temperature. May I ask, at temperatures below 230°C, ① the atmosphere contains only H2S and no hydrogen; we are waiting for H2S to penetrate through the catalyst bed ； ②After the exothermic wave of the sulfidation reaction passes through the catalyst bed (with a temperature rise of about 20–30°C), hydrogen sulfide penetrates. At this point, hydrogen is introduced again, while the inlet temperature is increased; by controlling the concentrations of H2S and H2 at appropriate levels, pre-sulfidization is carried out. May I ask, what is the effect of pre-vulcanization in this vulcanization process? Step ①: H2 and H2S are introduced simultaneously to ensure that the H2S penetration and the sulfidation process in the low-temperature zone occur at a temperature below 230°C; is this approach more effective? Thank you!