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

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

Robust In Situ Magnetic Resonance Imaging of Heterogeneous Catalytic Hydrogenation with and without Hyperpolarization

ISSN:1867-3880ISSN:1867-389

Breaking structure sensitivity in CO2 hydrogenation by tuning metal–oxide interfaces in supported cobalt nanoparticles

A high dispersion of the active metal phase of transition metals on oxide supports is important when designing efficient heterogeneous catalysts. Besides nanoparticles, clusters and even single metal atoms can be attractive for a wide range of reactions. However, many industrially relevant catalytic transformations suffer from structure sensitivity, where reducing the size of the metal particles below a certain size substantially lowers catalytic performance. A case in point is the low activity of small cobalt nanoparticles in the hydrogenation of CO and CO2. Here we show how engineering of catalytic sites at the metal–oxide interface in cerium oxide–zirconium dioxide (ceria–zirconia)-supported cobalt can overcome this structure sensitivity. Few-atom cobalt clusters dispersed on 3 nm cobalt(II)-oxide particles stabilized by ceria–zirconia yielded a highly active CO2 methanation catalyst with a specific activity higher than that of larger particles under the same conditions

Breaking structure sensitivity in CO\u2082 hydrogenation by tuning metal-oxide interfaces in supported cobalt nanoparticles

A high dispersion of the active metal phase of transition metals on oxide supports is important when designing efficient heterogeneous catalysts. Besides nanoparticles, clusters and even single metal atoms can be attractive for a wide range of reactions. However, many industrially relevant catalytic transformations suffer from structure sensitivity, where reducing the size of the metal particles below a certain size substantially lowers catalytic performance. A case in point is the low activity of small cobalt nanoparticles in the hydrogenation of CO and CO2. Here we show how engineering of catalytic sites at the metal–oxide interface in cerium oxide–zirconium dioxide (ceria–zirconia)-supported cobalt can overcome this structure sensitivity. Few-atom cobalt clusters dispersed on 3 nm cobalt(II)-oxide particles stabilized by ceria–zirconia yielded a highly active CO2 methanation catalyst with a specific activity higher than that of larger particles under the same conditions