High-loaded Ni-SiO2 and Fe-SiO2 catalysts (85-90wt.% of metal) for methane decomposition were prepared by the heterophase sol-gel method and studied at various stages of their preparation and operation using XRD, IR, TPR, TEM techniques and the stoichiographic method of differentiating dissolution. Carbon yield was demonstrated to depend on the interaction between nickel and silica. The yield equal to 384 g C/g Ni was characteristic of the catalyst free of silicates, while the presence of silicates in amount of 1.5-2 wt.% caused a decrease in the carbon yield to 40 g C/g Ni. The effect of silicates comprised in iron catalysts is not so unambiguous as for nickel catalysts, they can both inhibit and promote the process of carbon formation.