The reaction between CH4 and framework oxygen of Pt promoted CexZr1-xO2 (x = 0.25, 0.5, 0.75, 1) solid solutions was studied at 873 K for syngas (CO + H-2) production. The homogeneity and cubic/tetragonal structure of the solid solutions were confirmed by powder X-ray diffraction. The thermodynamic properties of the solid solutions, connected with Ce4+/Ce3+ redox reactions, were measured by titrating the oxygen content of the oxides after equilibration in flowing mixtures of H-2 and CO2 with 10(-31) < pO(2) < 10(-22) atm. The transient reactions between the oxides and discrete pulses of CH4, as well as of isotopically labeled (CH4)-C-13 + (CO)-C-12 mixtures (limited to the material with x = 0.25) were investigated and reactivity, conversion and selectivity were measured. A strong correlation between the thermodynamic properties of the oxides and the syngas selectivity was found. The C-13 scrambling in CO and CO2 during co-feed experiments confirmed equilibration of these molecules with the oxides surfaces.