Chemical adsorbents for removing impurities from fuel; chemical adsorbents for the removal of oxygen and oxygen containing or oxygenated compounds from gas and liquid streams that contain inorganic sulfur compounds such as and not limited to hydrogen sulfide; iron-based chemical adsorbents for the removal of oxygen and oxygen containing or oxygenated compounds from gas and liquid streams that contain inorganic sulfur compounds such as and not limited to hydrogen sulfide