Several methods have been reported in the literature concern- ing the cobalt–silicon mixed oxide [29-31] among them the sol– gel technique. It is a better way for control the textural properties of the silica matrix as well as an effective way for cobalt-doping within the matrix on a nanometric scale [32,33]. Possible hypoth- esis for the interaction between cobalt species and silica matrix, prepared via sol–gel way, is the formation of Si–O–Co bridges. These bridges were suggested to be formed through the condensa- tion reaction between the silicone complexes [Si(OC2H5)4