Monometallic cobalt and bimetallic Co-Pt samples of various particle sizes have been prepared using SiO2 and synthetic kenyaite (layered silicate) as a support. They are characterized by elemental analysis, XRD, TPR, and XPS. Cobalt is introduced by two methods-classical impregnation and ammonia method. The ammonia method of preparation leads to the formation of finely dispersed Co3O4 on both supports. Besides, hardly reducible cobalt silicate phases appear predominantly on the SiO2 support. The Co3O4 particle size varies between 5 and 20 nm, depending on the support. The monometallic Co samples prepared by ammonia method on both supports are more active in benzene combustion than the impregnated ones due to the finer dispersion of the easily reducible Co3O4. Addition of Pt improves the activity and the promoting effect is more evident for the impregnated sample. This is explained with the synergy effect of cobalt oxide species and Pt. The less promoting effect of Pt on the catalytic activity of the bimetallic kenyaite-supported samples is attributed to the stronger interaction between the Co oxide phase and Pt during the preparation process.