The promoting effect of noble metal addition on niobia-supported cobalt catalysts

The promoting effects of a noble metal (Pd, Pt, Ph) added to Co/Nb2O5 catalysts were studied by varying the Me/Co atomic ratios. Acid niobium was calcined to niobium pentoxide. The surface and bulk structures of the calcined materials were characterized by XPS and TPR techniques. The catalytic performance was obtained with CO hydrogenation. The addition of a noble metal promoted the reduction of Co3+ and Co2+ phases at the surface. XPS results revealed that Co2+ species are well dispersed as a thin layer around the niobium support together with Co3O4 crystallites islands. The Co3O4/Co2+ ratio depends on the surface area of the support. XPS measurements also revealed that PdO, Rh2O3 and PtO2 are the main phases in the mono and bimetallic catalysts. The activity of the bimetallic catalysts increased and the stability was already attained. The selectivities towards C-5(+) and oxygenates increased with the addition of Ph up to an atomic ratio of 0.5 and decreased beyond that. This behavior is similar for both temperatures of reduction at 573 and 773 K.