Gold-Perovskites Supercharge Clean Acetaldehyde from Ethanol

• Gold on Cu-doped LaMnO3 converts ethanol to acetaldehyde at 95% yield, 225°C, 715 gAC gAu−1 h−1—Au–Mn–Cu synergy delivers, while excess Cu stalls activity.

Researchers at Huazhong University of Science and Technology and Eindhoven University of Technology report Au nanoparticles on Cu‑doped LaMnO3 (Au/LaMn0.75Cu0.25O3) that oxidize ethanol to acetaldehyde in air with 95% yield at 225°C and a space‑time yield of 715 gAC gAu−1 h−1, showing durable performance and outperforming Au/MgCuCr2O4.

DFT‑microkinetic analyses reveal Au–Mn–Cu cooperation: moderate Cu creates adjacent Cu+ and Mn2+ near Au, enabling O–H cleavage by lattice oxygen and α‑C–H cleavage on Au. Reoxidation proceeds via O2 adsorption and peroxide intermediates; water formation is rate‑determining. Excess Cu yields metallic/Cu2+ domains, disrupting active ensembles and suppressing activity.

How does Au–Mn–Cu synergy enable selective ethanol oxidation at 225°C?

• Interfacial ensembles: the Au perimeter adjoining Cu- and Mn-cations creates bifunctional sites where alcohol activation and dehydrogenation steps occur cooperatively.
  
• Tuned redox pairs: Cu substitution adjusts Mn valence, generating neighboring Cu+–Mn2+ centers and oxygen vacancies that supply labile lattice oxygen right next to Au.
  
• Ethanol activation sequence: ethanol adsorbs on Lewis-acidic cations; O–H scission proceeds via lattice O at Cu/Mn sites to form ethoxy; α-C–H cleavage occurs on Au, yielding acetaldehyde that desorbs readily, preserving selectivity.
  
• Mars–van Krevelen closure: vacancies produced during O–H cleavage are reoxidized by O2 taken up at the Au–oxide boundary, with superoxo/peroxo intermediates mediating electron–proton transfers.
  
• Turnover control: water formation from surface O/O2-derived species and hydrogen is the slow step, setting the overall rate at 225°C.
  
• Electronic moderation: Au polarizes/reacts at the perimeter to lower α-C–H barriers, while Cu weakens oxygen over-reactivity, avoiding deep oxidation to COx.
  
• “Goldilocks” Cu loading: moderate Cu maintains contiguous Au–Cu–Mn ensembles; excess Cu segregates into Cu0/Cu2+ domains that break the cooperative sites and dampen activity/selectivity.
  
• Oxygen mobility: the perovskite lattice provides fast oxygen diffusion at 225°C, sustaining rapid lattice-O participation without accumulating overly reactive oxygen.
  
• Selectivity lever: constrained oxygen reactivity at the interface suppresses C–C scission and acetate/COx pathways; acetaldehyde leaves before further oxidation.
  
• Durability factors: reversible Mn/Cu redox cycling, stabilized small Au particles, and efficient removal of interfacial hydroxyls limit sintering and coking under air.
  
• Performance enablers: high perimeter density and strong Au–perovskite coupling deliver high space–time yield with air as oxidant, outperforming spinel supports that bind oxygen either too weakly or too strongly.