Influence of cobalt species on the catalytic performance of Co-N-C/SiO2 for ethylbenzene oxidation

In this paper, cobaltporphyrin is used as a precursor to synthesize carbon nitrides with metal active sites supported on silica spheres by heat treatment (i.e. M-N-C/SiO2). The catalytic performance of M-N-C/SiO2 for ethylbenzene oxidation has been investigated and techniques such as N-2 adsorption/desorption isotherm, NH3-TPD, HRTEM, STEM mapping and X-ray photoelectron spectroscopy (XPS) are employed to explore the active sites for ethylbenzene oxidation. XPS results show that cobalt compounds, such as CoOx and metallic Co, as well as cobalt nitrides, such as Co-N-x, are formed after the pyrolysis of cobaltporphyrin. However, according to the NH3-TPD experiment, Co-N-x may be the primary active site. When Co-N-x is poisoned by KSCN, the significant loss of catalytic activity further proves and verifies that Co-N-x instead of CoOx is the primary active site of M-N-C/SiO2 for ethylbenzene oxidation.