Thermodynamics and kinetics of CO₂ adsorption on dehydrated palladium/cobalt-based cyanogels: A highly selective, fully reversible system for CO₂ storage

Carbon dioxide is selectively adsorbed on cyanide-bridged palladium/cobalt gels, synthesized from aqueous solutions of Na₂PdCl₄ and K₃[Co(CN)₆]. The cyanide bridges, connecting the palladium and cobalt metal centers, are characteristic of these gels; hence, these gels are termed cyanogels. The thermodynamics and kinetics of the CO₂ adsorption and desorption processes on aerogels and xerogels formed from Pd/Co cyanogels are analyzed here. Aerogel versus xerogel structures have a profound effect on the thermodynamics and kinetics of CO₂ adsorption. The CO₂ adsorption process is fully reversible on both types of gels discussed. The gas adsorption capacity of the aerogel exceeds that of the xerogel by a factor of slightly over two. From the ease and reproducibility of the CO₂ desorption and the associated enthalpy values, it is concluded that CO₂ is physisorbed on these gels. The kinetics of adsorption and desorption are analyzed: both processes are first-order in the gels.