Calcium hydroxide, Ca(OH)(2), was impregnated with different sodium compounds, namely, NaOH, Na2O, Na2O2, NaNH2, Na2CO3, Na2SO3, NaBH4, and dried and calcined (650-800 degrees C). The nature of structural changes in the different mixed composites during the course of calcination was studied using different analytical techniques, i.e. DSC, IR, and XRD. The results indicate that a solid-solid interaction develops between NaOH, which was also formed as an intermediate from the other sodium compounds employed, and the Ca(OH)(2) matrix, even after oven-drying at 120 degrees C. The measured lattice parameters indicate that the inclusion of Na+ ions in the CaO matrix remains very limited on calcining the samples at 650 degrees C. It may be presumed that most of sodium oxide/hydroxide remains in a well-dispersed state over the CaO matrix. The use of different sodium compounds does not show any significant differences in C-2+ selectivity and activity for the oxidative coupling of methane.