We report the synthesis and characterization of a selective nitric oxide (NO) adsorbent based on the covalent binding of cobalt(II) phthalocyanine tetrasulfonic acid (CoPcS) onto imidazole-functionalized mesoporous silica gel beads. The equilibrium data indicated that the adsorption of NO was highly favorable, approaching irreversible adsorption. The breakthrough curves for NO were modeled assuming irreversible adsorption and resulted in pore diffusivities through the packed bed of 0.1-0.3 cm(2).s(-1). Adsorption experiments of NO in the presence of nitrogen, water vapor, and ammonia indicated that the adsorption was selective for NO.