# Exploring Ortho–Para Hydrogen Conversion Catalysts Based on Surface Electric Field Gradient

## TL;DR

Researchers discovered new catalysts for converting ortho-hydrogen to para-hydrogen using insulating oxides with high ionicity and transition metal cocatalysts.

## Contribution

New oxide-based catalysts with high para-hydrogen conversion efficiency were identified using lattice energy as a design criterion.

## Key findings

- 5%Fe-loaded SiO2 achieved 50% para-H2 within 20 minutes at 77 K.
- Cocatalyst nanoparticles (1–12 nm) adsorb hydrogen without dissociation.
- Nuclear spin relaxation enhances conversion via quadrupole interaction on asymmetric oxide surfaces.

## Abstract

According to our
hypothesis that ortho (O) to para (P) hydrogen
conversion is promoted by an inhomogeneous electric field on the surface
of the insulating oxide with high ionicity, we searched for OP conversion
catalysts using lattice energy as an indicator of high ionicity. As
a result, we found new oxide catalysts, including SiO2,
γ-Al2O3, and CeO2 combined
with 3d late transition metal cocatalysts. The fraction of para-H2 on 5%Fe-loaded SiO2 powder reached 50% (equilibrium
value at 77 K) within 20 min. The activities of these catalysts are
significantly superior to those of benchmark catalysts, such as Mn3O4. The cocatalyst nanoparticles of 1–12
nm size dispersed on the oxide catalysts adsorb hydrogen well without
dissociating it. The nuclear spin state of ortho-H2 adsorbed
at the asymmetric site (nonzero electric field gradient) of the oxide
surface is thermally excited by nuclear quadrupole interaction, and
the OP conversion rate is increased by nuclear spin relaxation.