Why can’t steam be used to displace the fully reduced catalyst?

To improve activity at low temperatures, low-temperature catalysts contain alkali metals; however, when steam is used for replacement, condensate forms within the micropores of the catalyst particles, leading to the loss of alkali metals, a decline in catalyst activity, and a reduction in the catalyst’s strength. In severe cases, clumping may also occur

Primarily, cobalt-molybdenum-based conversion catalysts suffer from sulfidation under high gas-to-vapor ratios, which leads to a decrease in their activity.

Under certain conditions, the metal sulfides, which are the active components of cobalt-molybdenum-based sulfur-resistant shift catalysts, transform into metal oxides and release hydrogen sulfide, thereby rendering the shift catalyst inactive; this phenomenon is known as the desulfurization reaction of sulfur-resistant shift catalysts. The main phenomena are the oxidation of MoS2 and sulfur release. Its reaction equation is: MoS2 + 2H2O = MoO2 + 2H2S. The main reasons for this desulfurization reaction are abnormal process operating conditions, such as too high an inlet temperature, too low a hydrogen sulfide content in the gas, and a too high gas-to-steam ratio. Replacing with steam can cause sulfidation of cobalt-molybdenum-based sulfur-resistant shift catalysts, leading to a decrease in their activity; therefore, cobalt-molybdenum-based sulfur-resistant shift catalysts must never be replaced with steam. I wonder if the original poster understands?

If the catalyst has low temperature and is inactive, it can also lead to a loss of activity! If you want to replace the catalyst, you can use this method to swap it out!