Solvent-free oxidation of cyclohexane by oxygen over Al-Cu-Co alloys: Influence of phase structure and electrical conductivity on catalytic activity
Al-Cu-Co alloys containing different intermetallic compound phases were fabricated by the arc-melting method and used as the heterogeneous catalyst for the solvent-free cyclohexane oxidation by oxygen. The element composition and bulk structure were characterized by ICP-OES, XRD, SEM, TEM and XPS. Co species were the major active component and a small amount of Cu dissolved in the Al13Co4 phase of the alloy exhibited a synergetic effect on improving the catalytic activity. The Cu dissolved in the Al13Co4 phase that was a decagonal quasicrystal approximant with special atomic arrangement structure could increase the electrical conductivity and accelerate the electron transfer during the catalytic oxidation of cyclohexane, and thus improved the catalytic activity of the alloy. Among all alloys prepared in the present work, Al60Cu5Co35 alloy exhibited the best catalytic performance with a conversion of cyclohexane of 6.4% and a total selectivity of 95.2% to cyclohexanol and cyclohexanone. No significant change in the catalytic activity of Al60Cu5Co35 alloy was observed after five cycles.