TG/DTA, TPR and TPO characterization of Co/SiO2 nanocomposites

Co/Si oxide systems were prepared by a modified sol-gel method starting from Co(NO3)2.6H2O and Si(OC2H5)4 without any alcoholic solvent and characterized by TG/DTA, XRD, TPR and TPO techniques. The sample with lowest Co content was amorphous up to 900°C, while nanocrystalline Co3O4 (size = 12-13 nm) was formed even at 400°C in the Co richest samples: Co silicate was formed in all samples at 800-900°C. The Co+2 species present at low Co/Si ratio appeared hardly reducible, while the Co3O4 phase present at high Co/Si ratio was easily reduced. Treatment at 600°C caused a decrease of the amount of Co3O4 and an increase of the more strongly bonded Co. The reoxidation of Co(0) became easier with increasing Co content. Reduction/oxidation cycles led to less reducible species, due to formation of stronger bonds with the siloxane framework