The reduction of cobalt (Co) catalyst supported on silica nanosprings for Fischer-Tropsch synthesis (FTS) has been monitored by X-ray photoelectron spectroscopy (XPS) and compared to FT catalytic activity. The cobalt is present in the starting catalyst as a Co3O4 spinel phase. A two-step reduction of Co3O4 to CoO and then to Co-0 is observed, which is consistent with the results of H-2-temperature programmed reduction. During the reduction the two steps occur concurrently. The deconvolution of the Co 2p core level state for the catalyst reduced at 385 degrees C and 1.0 x 10(-6) Torr of H-2 revealed signatures of Co-0, CoO, and Co3O4. The reduction saturates at a Co concentration of approximately 41% after 20 h, which correlates with the activity and lifetime of the catalyst during FTS testing. Conversely, at 680 degrees C and 10 Torr of H-2, the catalyst is completely reduced after 10 h. The evolution of the Co d-band at the Fermi level in the valence band XPS spectrum definitively verifies the metallic phase of Co. FTS evaluation of the Co/NS catalyst reduced at 609 degrees C showed higher production rate (3-fold) of C-6-C-17 hydrocarbons than the catalyst reduced at 409 degrees C and is consistent with the XPS analysis. (C) 2015 Elsevier B.V. All rights reserved.