Unveiling the Au-Mn-Cu synergy in Au/LaMnCuO3 catalysts for selective ethanol oxidation

Gold nanoparticles (AuNPs) supported on the Cu-doped LaMnO3 perovskites exhibit strong Au-Mn-Cu synergy in the aerobic oxidation of gaseous ethanol to acetaldehyde (AC). The Au/LaMnCuO3 catalysts achieve AC yields exceeding 90% and a space-time yield of 715 gAC gAu –1 h–1 at 225 °C, outperforming reported catalysts. The outstanding performance is attributed to adjacent Cu+ and Mn2+ ions in the perovskite surface, which, together with nearby AuNPs, contribute to the high activity and stability. The best-performing catalyst contains a Cu/Mn ratio of 1/3 in the perovskite. Doping too much Cu into the perovskite leads to metallic Cu, suppressing catalyst performance. Density functional theory (reaction energetics, electronic structure analysis) and microkinetics simulations aided in understanding the synergy between Cu and Mn and the role of AuNPs. The reaction involves two H abstraction steps: (1) O–H cleavage of adsorbed ethanol by the basic perovskite lattice oxygen atom and (2) α-C-H cleavage by AuNPs, yielding AC and adsorbed water. Molecular O2 adsorbs in the oxygen vacancy (OV) formed by water removal, generating a peroxide anion (O2 2–) as the activated oxygen species. In the second part of the catalytic cycle, the basic O2 2– species abstracts the H atom from another ethanol molecule, followed by α-C-H cleavage by AuNPs, AC production, and water removal. Water formation in the second part of the catalytic cycle is the rate-controlling step for Au/LaMnO3 and Au/LaMnCuO3 models. Moderate Cu doping enhances the essential Cu+-OV-Mn2+ sites and lowers the barrier for water formation due to the weaker Cu–O bond than the Mn–O bond. In contrast, excessive Cu doping creates unstable Cu2+-O-Cu2+ sites and shifts the barrier to the α-C-H cleavage.