Impregnated active carbons to control atmospheric emissions. 2. Influence of the raw material on the porous texture.
The preparation of impregnated active carbons was optimized, in order to use them as catalysts for the deep oxidation of volatile organic compounds on atmospheric emissions. When impregnation is performed on the raw material or after activation, the influence of raw material on the texture and on the catalyst dispersion is already well studied. This paper aims to analyze the influence of raw material when the impregnation step is performed after the carbonization of different carbon precursors, as yet knowledge is very scarce. Olive stones, pinewood sawdust, nut shells, and almond shells were used as raw materials. In order to evaluate the influence of impregnation methodology of CoO, Co(3)O(4), and CrO(3) on the catalyst dispersion in the porous carbon texture, the impregnation step was made after activation and between carbonization and activation. On the first sequence, for all the raw materials, the impregnated oxides must be deposited on the internal surface, blocking part of the initial porous texture. When the impregnation step is conducted after carbonization, metal species act as catalysts during the activation step. The textures developed strongly depend either on the raw material or on the chemical state and distribution of the catalyst in the carbonized material. Olive stones and sawdust carbons stay with a microporous texture with very narrow pores where catalysts are not deposited. In nut shell and almond shell carbons, metal species are dispersed in the largest micropores and in a well-developed mesoporous texture.
Alvim-Ferraz
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LEPAE, Departamento de Engenharia Qui;mica, Faculdade de Engenharia, Universidade do Porto, Porto, Portugal. aferraz@fe.up.pt
Todo-Bom Gaspar
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