The acidity and basicity of silica-supported nickel catalysts modified by metallic additives such as Fe, Co, Zr and Ce have been determined by adsorption microcalorimetry. These catalysts have been tested in the catalytic reforming of methane with carbon dioxide. The results indicate that the metallic additives modify noticeably the acidity of the Ni/SiO2 catalysts, the acidity increasing in the order : Ni-Ce < Ni < Ni-Co < Ni-Fe < Ni-Zr. Moreover, it was demonstrated that the most active catalyst in the CH4 + CO2 reaction is the least acidic, namely, Ni-Ce/SiO2.