Determination of cobalt species in niobia supported catalysts

Niobia-supported cobalt catalysts were prepared by incipient wetness impreg nation and were characterized by X-ray diffraction (XRD), diffuse reflectan ce spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), temperature- programmed reductioon (TPR) and magnetic measurements. At least two differe nt types of cobalt species were present on the calcined catalysts: Co3O4 pa rticles and Co2+ surface species. At high cobalt content, Co3O4 particles a re the main species whereas the percentage of Co2+ species linked to the su pport increases as the cobalt loading is decreased. XPS results revealed th at the Co2+ species could be better represented by a mixture of Co2Nb5O14 a nd CoNb2O6. TPR analyses allowed one to quantify the percentage of Co3O4 pa rticles on the niobia-supported Co catalyst. However, due to partial reduct ion of niobia, TPR alone did not permit the quantification of the reduction degree of cobalt in these catalysts. Magnetic measurements linked to a TPR technique is a possible way to measure the reduction degree of cobalt in C o/Nb2O5 catalysts. After reduction at high temperature, the mixture of coba lt niobates was reduced and NbO2 produced led to the strong metal-support i nteraction (SMSI) effect.