Heterogenization of porphyrin complexes within the nanocages of SBA-16: New efficient and stable catalysts for the epoxidation of olefins

Abstract

Heterogenization of two manganese porphyrins i.e. 5,10,15,20-tetrakis(4-isopropylphenyl) porphyrin-Mn(III) chloride (MnTIPP) and 5,10,15,20-tetrakis(4-butoxyphenyl) porphyrin-Mn (III) chloride (MnTBPP) within the nanocages of SBA-16 was conducted via a novel encapsulation method, involving the initial inclusion of these catalytically active complexes followed by reducing the size of pore entrances through silylation with octyltriethoxysilane in order to prevent the possible release of these complexes from the nanocages. The successful encapsulation of these complexes was approved by different physicochemical techniques such as inductively coupled plasma optical (ICP-OES) spectroscopy, CHN elemental analysis, and energy dispersive X-ray (EDX) analysis. X-ray diffraction (XRD) and transmittance electron microscopy (TEM) showed that the microstructure of the SBA-16 was retained after heterogenization of the complexes. However, the nitrogen adsorption-desorption analysis (BET method) illustrated that the surface area of the SBA-16 decreased after inclusion of the complexes within the nanocages. Catalytic properties of the prepared catalysts were investigated in the epoxidation of olefins using sodium hypochlorite as oxidant and imidazole as co-catalyst. The catalysts exhibited high catalytic activity and selectivity in mild reaction conditions and recycled five times without considerable loss of efficiency. The homogeneous Mn (III) porphyrins trapped inside the nanocages have no any interaction with silica wall of SBA-16 and thus have good catalytic activities. On the other hand, due to the limited size of the pore entrances they cannot escaped from the nanocages which results in the catalyst stability and superiority for production of various epoxides.