Active carbons impregnated before activation of olive stones: catalytic activity to remove benzene from gaseous emissions

Abstract

This work analyses the catalytic activity of impregnated active carbons prepared with olive stones to remove benzene from atmospheric emissions through catalytic complete oxidation. When the impregnation step is performed on the raw material or after activation, the influence of carbon texture on the catalyst dispersion and catalytic activity is already well studied. Nevertheless, when the impregnation step is performed before activation, the knowledge about catalytic activity is yet very scarce, being the main objective of the study here reported. Not expensive metal oxides were used as active species: CoO, Co 3O 4 and CrO 3. At 523 K, the kinetic constants are 2.3–2.6 times higher when impregnation is performed before activation, due to a better catalyst distribution associated with a better development of mesoporous texture. Co 3O 4 is the best catalyst for the activation step and for the complete oxidation of benzene, the kinetic constant being 2.1 times higher than when the impregnant is CrO 3, the worst of the catalyst studied. To reach 90% of benzene conversion using Co 3O 4 as catalyst, a reduction of 12% in temperature was possible, when compared with CrO 3. Nevertheless, all the catalysts allow good conversions at temperatures lower than 575 K, above which the carbon stability cannot be guaranteed.