Hydrous ferric oxide (sold as “Ionex-Type OP Catalyst“ by Molecular Products, short Ionex) is the most widely used catalyst for ortho-para conversion in hydrogen liquefaction. Activation of the catalyst requires conditions that often conflict with certain practical limitations, such as heat exchanger temperature constraints. This work evaluates practical activation procedures for Ionex under application-oriented constraints.The maximum activity was obtained by flushing with hydrogen at 140–160 °C for 16 h; overheating above 160 °C caused a sharp performance loss. Using lower temperatures, the activity decreased to ∼94% (120 °C), ∼88% (100 °C), ∼80% (80 °C), and ∼70% (60 °C) of the maximum value. Using sub-atmospheric activation pressures combined with hydrogen purge enhanced the activation; vacuum-only activation proved less effective. These results provide a guideline for activation under diverse practical boundary conditions and allow for bed volume scaling to account for incomplete activation.