Branching-chain propagation of parahydrogen-derived nuclear spin order on a catalyst surface

06 October 2023, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


When a parahydrogen molecule dissociates on a surface of a heterogeneous catalyst (e.g., of a metal nanoparticle), the correlation of the nuclear spins initially inherited by the two surface H atoms may be shared with other surface hydrogens as they diffuse and combine with random H atoms to produce H2 molecules which subsequently dissociate. This branching-chain-type propagation of nuclear spin order leads to its gradual dilution but at the same time is accompanied by an increase in the number of H atoms that share nuclear spin order. These conclusions, confirmed by the spin density matrix calculations, may be relevant in the context of parahydrogen-induced polarization (PHIP) in heterogeneous hydrogenations catalyzed by supported metal catalysts, observation of which apparently contradicts the accepted non-pairwise mechanism of hydrogen addition to an unsaturated substrate over such catalysts. The potential consequences of the reported findings are discussed in the context of PHIP effects and beyond.


nuclear spin order
heterogeneous hydrogenation
H2 activation on metals

Supplementary materials

Spin density matrix calculations of spin order propagation
Spin density matrix formalism, spin system parameters, and calculation of the spin ensemble for three- and four-spin systems


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