Two-dimensional Zr-TCPP(Fe) with nanoflower structure not only provides fully exposed accessible active sites but also reduces substrate/product transfer resistance, thus showing excellent catalytic performance for styrene epoxidation and benzylic C−H oxidation reactions using O₂ as sole oxidant under ambient temperature and pressure.

Abstract

Selective oxidation of hydrocarbons using molecular oxygen as sole oxidant under mild conditions remains a challenging task. In this context, metal-organic frameworks (MOFs) have been widely used in various oxidation reactions due to their porosity, high surface area and designability. However, the slow diffusion of substrates/products in micropores of three-dimensional (3D) bulk MOFs hinders the efficient catalytic performance of such materials. Herein an ultrathin two-dimensional (2D) porphyrin-based Zr-MOF nanosheet (Zr-TCPP) is synthesized through modulator-control strategy. Subsequently, various metal ions are anchored into the porphyrin ring by post synthesis modification to afford a series of 2D Zr-TCPP(M) (M=Mn, Fe, Co, Ni, Cu and Zn). Various structural characterization techniques indicate Zr-TCPP(M) is nanoflower structure with ultrathin nanoplate petals which provides fully exposed accessible active sites. Among them, Zr-TCPP(Fe) shows excellent catalytic performance in styrene epoxidation reactions and benzylic C−H oxidation reactions using O₂ as sole oxidant under ambient temperature and pressure. The remarkable activity arises from high density of exposed porphyrin-Fe active sites, low diffusion barriers for substrates and products, as well as a similar homogeneous reaction space. Furthermore, Zr-TCPP(Fe) nanosheet is easily recycled by centrifugation and reused at least five times without significant loss of catalytic activity.