Design, fabrication and the relative catalytic properties of metal–organic framework complexes based on tetra(4-carboxyphenyl)porphyrin and cerium ions

Two metal-organic framework compounds composed of cerium ions coordinated with tetra(4-carboxyphenyl) porphyrin H sub(2)TCPP (3) and its cobalt congener CoTCPP (4), namely H sub(2)TCPP/Ce (1) and CoTCPP/Ce (2) were synthesized. Their self-assembly behaviors were systematically investigated using electronic absorption spectra, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and energy dispersive X-ray spectroscopy (EDX). The formation of H sub(2)TCPP/Ce (1) nanoparticles with an average diameter of 500 nm depended mainly on the Ce-O coordination bond between the additive cerium ion and the oxygen atom of the carboxy group of the porphyrin 3 molecule. However, additionally formed Co-C coordination bonds between the central cobalt ion of 4 to the carbon atom of the adjacent porphyrinato 4 ring, in combination with Ce-O coordination bond between the additive cerium ion and the oxygen atom of the carboxy group of porphyrinato 4 molecules, induced the formation of CoTCPP/Ce (2) nanoparticles with apparently smaller average diameters (380 nm). After calcining the corresponding H sub(2)TCPP/Ce (1) and CoTCPP/Ce (2) metal-organic frameworks, two types of morphology-preserved CeO sub(2) were obtained, both of which showed excellent catalytic properties towards the oxidation of CO to CO sub(2).