Catalysis
Single-atom Co–N–C catalyzes nitroarene azo coupling
Open access · cc by · source: Europe PMC
A self-supporting Co–N–C single-atom catalyst with a CoN4C8-1-2O2 site hydrogenatively couples nitroarenes to azo compounds.
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
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
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.
Methodology
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.
Limitations
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.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
This library holds 8 empirical chemistry papers on catalysis with isolated findings, rates or spectra rather than reviews.
Evidence for the claim as stated.
A self-supporting Co–N–C single-atom catalyst with a CoN4C8-1-2O2 site hydrogenatively couples nitroarenes to azo compounds.
Evidence for the claim as stated.
Heterogeneous, molecular and dual photoredox/metal systems are not interchangeable; support, ligand and light each change the active site.
Evidence for the claim as stated.
XPS also reports how much metal is actually on a molecular or pyrolysed catalyst. A pyrolysis-free Fe–PIPhen on Vulcan XC-72 has 0.748 at% Fe, onset ~0.85 V, average n = 3.94 at 1600 rpm, and H₂O₂ yield 1.6–3.1% (k₁/k₂ = 30–50). A Co–N–C material identified as isolated Co²⁺ in a CoN₄C₈-1-2O₂ motif (XPS with XANES/EXAFS/STEM) gives 97% azo yield and TOF 35.9 h⁻¹ — still without in-operando proof of the hydrogenation cycle.
Evidence for the claim as stated.
XPS is a surface vote; XRD/STEM decide how that vote relates to the bulk. The Ni CO₂ paper uses missing Ni–N XPS intensity plus 10–100 nm STEM particles to reject a single-atom picture; the Co–N–C paper uses XPS with EXAFS to assert isolated CoN₄. Same spectroscopy, opposite structural conclusions, because the materials differ — you cannot treat 'XPS showed the metal state' as portable.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Heterogeneous, molecular and dual photoredox/metal systems are not interchangeable; support, ligand and light each change the active site.
- Supports · Ru dimer vs monomer splits CO from formate
XPS is a surface vote; XRD/STEM decide how that vote relates to the bulk. The Ni CO₂ paper uses missing Ni–N XPS intensity plus 10–100 nm STEM particles to reject a single-atom picture; the Co–N–C paper uses XPS with EXAFS to assert isolated CoN₄. Same spectroscopy, opposite structural conclusions, because the materials differ — you cannot treat 'XPS showed the metal state' as portable.
Related papers in this topic
Same topic cluster — not a recommendation engine.