Exploration of heterogeneous catalyst for molecular hydrogen ortho-para conversion

Molecular hydrogen (H₂) ortho-para conversion (O/P conversion) proceeds slowly at low temperatures accompanying a heat release. Thus, catalysts for accelerating this conversion rate are highly demanded in terms of the storage and utilization of liquid H₂. The catalysts for this purpose are experimentally screened by examining a broad range of materials covering magnetic, non-magnetic, metallic, and nonmetallic oxides. The primary conclusions obtained are summarized below. (1) active materials are required to be non-metallic and to bear the cations with ionic radii smaller than the bond length of H₂. (2) Metallic materials have almost no activity irrespective of with or without magnetism (3) The activity of materials belonging to (1) is largely enhanced when the constituting cation has a magnetic moment. In addition, there is a class of materials for which the activity is distinctly enhanced just upon substitution by the foreign ions.