Micropore Size Distribution of Activated Carbons Impregnated After Carbonization

Abstract

Impregnated active carbons were prepared to be used as catalysts of complete oxidation, aiming the reduction of atmospheric emission of volatile organic compounds. The onversion efficiency is regulated by the catalyst dispersion in the porous structure where pollutants can access to be converted, which means that a good dispersion is required. Therefore, microporore size distribution has an important role on the catalyst efficiency, either because the access to the catalyst can be made through micropores, or because micropores can offer a significant deposition surface, if they are wide enough. When the impregnation is performed on the raw material or after activation, the micropore size distribution is already well studied. This paper aims to analyse that distribution when impregnation is performed after carbonization, because this knowledge is yet very scarce. Nut and almond shells were used as raw materials to prepare carbons impregnated with CoO and Co₃O₄. The comparison between the micropore size distributions was performed using Medek model. When impregnation is made after activation, it was concluded that, for both raw materials, the catalysts block part of the initial microporous structure, leading to a decrease in micropore volume and to an increase of the mean equivalent radius. When impregnation step is conducted after carbonization, the total micropore volume can increase or decrease in relation to the non-impregnated carbons, depending on the catalyst distribution and type of carbonized support. Nevertheless, all the carbons analysed showed that impregnation after carbonization increases micropore volume of wider micropores.