A major challenge for hydrogen liquefaction is the required catalytic ortho-para hydrogen conversion. Efficient liquefaction plants use catalyst-filled plate-fin heat exchangers for the conversion. Kinetics of the allotropic reaction are determined using raw literature data on common first-order and a Langmuir-Hinshelwood kinetics, including temperature and molar concentration dependencies. Evaluation and comparison of the obtained kinetics results in the first-order approach as the most stable model. A one-dimensional continuum reactor model of the counterflow-cooled, catalyst-filled plate-fin heat exchanger is developed and tested combining correlations for heat, mass, and momentum transfer as well as a state-of-the-art equation-of-state.