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.
Source
Single-atom dispersed Co-N-C catalyst: structure identification and performance for hydrogenative coupling of nitroarenes
Study at a glance
- Design
- Other — Co–N–C single-atom catalyst identification by STEM/XAS and nitroarene hydrogenation tests
- N
- Heterogeneous catalysis materials study — no sample N
- Population
- Co–N–C catalysts converting nitroarenes
- Outcome
- CoN4 site structure and azo-product yield/TOF
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Inspect source passages
Single-atom Co–N–C catalyzes nitroarene azo coupling
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Co loading was 3.6 wt% with 0.09 wt% residual Mg.
Elemental analysis of the as-prepared Co–N–C catalyst revealed a Co loading of 3.6 wt% while the Mg residue was almost negligible (0.09 wt%).
Isolated azo yield reached 97% under optimized conditions.
Under the optimized reaction conditions (80 °C, 3 MPa H 2 , 1.5 h, tert -butyl alcohol as the solvent, catalyst loading of 0.7 mol% Co, 0.2 equivalent of NaOH), the isolated yield of azo reached 97%.
What they did
Authors pyrolyzed Co(phen)2(OAc)2 on Mg(OH)2, leached the support, and identified the Co site with HAADF-STEM, XANES/EXAFS, XPS and DFT, then tested nitroarene hydrogenation.
What they found
Co is isolated as Co2+ in a CoN4C8-1-2O2 motif (four pyridinic N plus weakly bound axial O). Optimized conditions give 97% azo yield, TOF 35.9 h–1, alkene-tolerant chemoselectivity, and reuse.
The limits
What it doesn't show
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.
Key terms
- Single-atom catalyst (SAC)
- Catalyst in which metal sites are atomically isolated rather than clustered as nanoparticles.
- Co–N–C
- Cobalt and nitrogen co-modified carbon obtained by pyrolysis of N-ligand complexes.
- XANES/EXAFS
- X-ray absorption methods that report oxidation state and local coordination of the absorber.
- Hydrogenative coupling
- Reduction of nitroarenes that condenses them to azo (Ar–N=N–Ar) products.
- TOF
- Turnover frequency: converted molecules per active metal atom per unit time.
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Quiz yourself
Assigned Co active-site formula:
Common questions
What is the proposed Co site?
CoN4C8-1-2O2: Co bound to four pyridinic N with two weakly adsorbed axial oxygens.
How was the support removed?
Mg(OH)2/MgO was leached with nitric acid after 700 °C pyrolysis.
What is the headline azo yield?
97% isolated yield under 80 °C, 3 MPa H2, 1.5 h.
Why are alkenes spared?
ATR-IR/controls indicate the alkene does not adsorb on Co–N–C sites.
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