Vanadyl acetylacetonate grafted on ordered mesoporous silica KIT-6 and its enhanced catalytic performance for direct hydroxylation of benzene to phenol

Abstract

Abstract The direct hydroxylation of benzene to phenol under H2O2 is one of the most important research topics in catalytic synthesis and green chemistry. As a conventional and widely available catalyst, vanadyl (IV) acetylacetonate [VO(acac)2] shows remarkable catalytic efficiency for the process, however is a typical homogeneous catalyst. In this work, ordered mesoporous silica (KIT-6) was applied to a new catalytic support to immobilize VO(acac)2. Several chacterization techniques including N2 adsorption–desorption, small and wide angle XRD, TEM, FT-IR, and XPS, have been used to analyze the physiochemical properties of the synthesized materials. VO(acac)2 was solidly immobilized on the amine-functionalized KIT-6 via the formation of Schiff base, while the original ordered mesoporous structure of KIT-6 has been remained after the incorporation of VO(acac)2. In the direct hydroxylation of benzene under H2O2, the KIT-6-NH2-V materials showed catalytic activities. The maximum catalytic yield of phenol obtained at 60 °C was ca. 17%. Furthermore, under the same reaction conditions, the immobilized VO(acac)2 catalyst exhibited superior catalytic activity to the catalysts supported on other two typical ordered mesoporous silicas (SBA-15 and FDU-12).