Atomic Structure and Valence State of Cobalt Nanocrystals onCarbon under Syngas Versus Hydrogen Reduction br

The composition of the reducing gas in the activation of Co Fischer-Tropsch synthesis catalysts determines the nature of the catalytically active Co species.This study reports on the effect of H2versus syngas (H2/CO = 2) on the reducibility ofCo3O4nanoparticles supported on hollow carbon spheres, usingex situandin situhigh-resolution aberration-corrected analytical electron microscopy. High-resolution imagesrevealed twinned fcc Co particles encapsulated in carbon from syngas treatment whileH2-treated particles were mostly CoO. Moreover, the electron energy loss of the Co-L3,2and O-K edgefine structures show improved reducibility in syngas than in H2at 350 degrees C.The effect of high temperature on the reducibility of the Co3O4nanoparticles is alsoexplored. Carbonfiber encapsulation of twinned fcc Co particles observed during the syngas treatment provides sinter resistance athigh temperatures. Bothex situandin situresults indicate that syngas activation is efficient for obtaining highly reduced Conanoparticles at lower temperatures