A method for making a class of relatively stable porous carbon dioxide absorbents by mixing inert nanoparticles with a CaO precursor followed by high temperature calcination. In the preferred embodiments of this invention this process takes place in the essential absence of nitrates. In some embodiments of the invention the method further includes forming the inert nanoparticles-doped porous CaO material by decomposing a mixture of inert particles and CaO precursor material.