Catalysis · Single-atom catalysts
A single-atom cobalt site, pinned down by imaging and X-ray spectroscopy, then put to work
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Short answer
An isolated CoN₄ site, assigned by four independent methods, hydrogenatively couples nitroarenes to azo compounds in 97% yield while leaving alkenes intact.
What happened
Liu and colleagues pyrolysed Co(phen)₂(OAc)₂ on Mg(OH)₂ at 700 °C and leached the support with nitric acid. HAADF-STEM, XANES/EXAFS, XPS and DFT together assigned a CoN₄C₈-1-2O₂ motif — cobalt bound to four pyridinic nitrogens with two weakly adsorbed axial oxygens. At 80 °C and 3 MPa H₂ for 1.5 hours, the catalyst gave 97% isolated azo yield with a turnover frequency of 35.9 h⁻¹, spared alkenes, and was reusable.
Why it matters
Single-atom catalysis claims often rest on one technique. Converging evidence from electron microscopy, X-ray absorption, photoelectron spectroscopy and theory is what makes the site assignment worth relying on — and the chemoselectivity is the practical payoff of having a site rather than a particle.
Evidence
- Study type
- Materials synthesis with HAADF-STEM, XANES/EXAFS, XPS and DFT site assignment, then catalytic testing
- Sample
- Heterogeneous catalyst study; no sample N
- Journal
- Chemical Science · peer reviewed
- Replication
- Not assessed in this corpus
- Limitations
- No in-operando evidence for the working cycle. Turnover frequency sits below some gold catalysts, and an acid-leached self-supporting film is not an industrial packed bed.
What this connects to
Sources
The 2 studies this explanation is built from, by the role each plays. Every source links to PaperFren’s explanation of it and to the original paper.
Primary study
- Single-atom Co–N–C catalyzes nitroarene azo coupling
A self-supporting Co–N–C single-atom catalyst with a CoN4C8-1-2O2 site hydrogenatively couples nitroarenes to azo compounds.
What it does not showLimitations
No in-operando proof of the working hydrogenation cycle; TOF is slightly below some Au catalysts; acid-leached self-supporting films may not match supported industrial beds.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Supporting evidence
- DFT: graphene SACs break CO2 scaling relations
Single metal atoms in graphene vacancies are predicted to reduce CO2 to methanol or methane at milder limiting potentials than metal terraces by weakening *CO more than *CHO.
What it does not showLimitations
These are 0 K computational limiting potentials, not measured electrolyzer FEs. Coverage effects are argued to be absent but not proven in situ. PBE plus empirical solvation can mis-order *COOH vs *OCHO. No new catalyst was synthesized in this paper.
PaperFren explanationStudy with cards and a quizOriginal paper (DOI)cc by
Before
Nitroarene reductions run on metal nanoparticles, where multiple adjacent metal atoms also reduce alkenes and other reducible groups, limiting selectivity.
Now
An isolated-site catalyst delivers the selectivity that particle surfaces cannot. The structure was determined before and after reaction rather than during it, so the working state of the site remains an inference.