Catalytic Ortho–Parahydrogen Conversion Over Platinum Group Metals (PGM)

Abstract

Efficient ortho-parahydrogen conversion (OPC) is essential for minimising boil off losses during hydrogen liquefaction and storage. This study compares the OPC performance of iron oxide catalyst from Molecular Products (commercially known as IONEX) with supported Platinum Group Metals (PGM) catalysts, which include 5 wt% Ru, Rh, and Pt supported on Al₂O₃. Catalyst samples with a 1 g mass were evaluated at 77 K and 1.2 barg over hydrogen flow rates of 0.3–3.0 SLPM. Outlet parahydrogen fractions were measured using a thermal conductivity detector, and apparent rate constants were determined using a first order kinetic model. The Rh/Al₂O₃ and Ru/Al₂O₃ catalysts exhibited rate constants of 483 and 401 min⁻¹, respectively, compared with 214 min⁻¹ for IONEX, while Pt/Al₂O₃ catalyst showed negligible activity at 13 min⁻¹. Structural, surface, and magnetic characterisation indicated that PGM activity is consistent with a dissociation recombination mechanism, distinct from the non-dissociative magnetic mechanism associated with IONEX. These findings identify Rh and Ru as promising catalysts for reducing converter size, pressure drop, energy losses, and costs in future industrial hydrogen liquefaction processes.