Methyl Group Modified MCM-41 Supported Schiff-Base Cobalt Complex and Its Catalytic Performance in Cyclohexane Oxidation

Abstract

The mesoporous molecular sieve MCM-41 was amino-functionalized using γ-aminopropyltriethoxysilane. The obtained NH2-MCM-41 was then hydrophobic modified by methyltriethoxysilane, dimethyldiethoxysilane and trimethylethoxysilane, respectively. N,N′-Bis (salicylidene) ethylenediiminocobalt (Cosalen) was grafting into the modified MCM-41 through the complex effect of NH2 group. The prepared Cosalen/(CH3)n–NH2–MCM-41 (n = 0, 1, 2, 3) were characterized by the technique of FT-IR, XRD, N2 adsorption–desorption, TG and so on. The catalytic performance of the Cosalen/(CH3)n–NH2–MCM-41 (n = 0, 1, 2, 3) for the cyclohexane liquid-phase oxidation by oxygen were compared. The results showed the selectivity of the polar product cyclohexanol and cyclohexanone significantly improved with the introduction of methyl groups into the surface of the MCM-41 carrier. Using Cosalen/CH3–NH2–MCM-41 as catalyst, the conversion of cyclohexane is 8.3 % under mild conditions with oxygen in absence of solvent, only 0.1 % cyclohexyl hydroperoxide was among the products, the total selectivity of the cyclohexanone and cyclohexanol is up to 93.6 %. Methyltriethoxysilane, dimethyldiethoxysilane and trimethylethoxysilane were used to modify the hydrophobic performance of the mesoporous molecular sieve MCM-41, the active component Cosalen was immobilized on the carrier through NH2 group after amino-functionalized using γ-aminopropyltriethoxysilane. In the solvent-free cyclohexane oxidation with molecular oxygen, the obtained Cosalen/CH3-NH2-MCM-41 as catalyst, the conversion of cyclohexane is 8.3 %, only 0.1 % cyclohexyl hydroperoxide was among the products, the total selectivity of the cyclohexanone and cyclohexanol is up to 93.6 %.