Single site anchored novel Cu(II) catalysts for selective liquid-gas phase O2 oxidation of n-alkanes

The pentacoordinate schiff-base trialkoxysilane Cu(II) complexes, i.e. Cu[Sal(PMeOSi)DPTA], (III-a) and Cu[Cl-Sal(PMeOSi)DPTA], (III-b) were synthesized and covalently anchored on SiO2 and Al2O3 matrixes as supported hybrid catalysts (i.e. III-a/SiO2 as Catal.-1, III-b/SiO2 as Catal.-2, III-a/Al2O3 as Catal.-3 and III-b/Al2O3 as Catal.-4). The characterization of supported Cu(II) complexes were performed with SEM-EDX, TGA,ICP, FT-IR and EPR analysis. Catalytic tests were conducted in the oxidation (O-2) of n-alkanes under relatively mild conditions, in a batch rocking type reactor. Remarkable high catalytic TONs, from 1468 up to 2422, were observed. Catal.-2 provided the best overall yield, 25.2% with 92% selectivity for n-hexane and 20.1% with 75% selectivity for n-heptane. A 20% improvement in the yields was obtained with PCA as co-catalyst. The impact of both C- and O- centred radical traps were also assessed in order to establish a radical mechanism. (C) 2012 Elsevier B.V. All rights reserved.