Effect of cobalt loading on reducibility, dispersion and crystallite size of Co/Al₂O₃ fischer-tropsch catalyst

Abstract

Co/Al₂O₃ Fischer-Tropsch synthesis catalysts with different cobalt loadings were prepared using incipient wetness impregnation method. The effects of cobalt loading on the properties of catalysts were studied by means of X-ray diffraction (XRD), temperature programmed reduction (TPR), hydrogen temperature programmed desorption (H₂-TPD) and O₂ titration. Co-support compound formation can be detected in catalyst system by XRD. For the Co/Al₂O₃ catalysts with low cobalt loading, CoAl₂O₄ phase appears visibly. Two different reduction regions can be presented for Co/Al₂O₃ catalysts, which belong to Co₃O₄ crystallites (reduction at 320°C) and cobalt oxidetallite size. The reduced Co/Al₂O₃ catalysts have two adsorption sites, and cobalt loading greatly influences the adsorption behavior. With the increase of cobalt loading, the amount of low temperature adsorption is increased, the amount of high temperature adsorption is decreased, and the percentage reduction and cobalt crystallite size are increased.

Keywords

Fischer-Tropsch synthesis / cobalt/alumina catalyst / temperature programmed reduction / hydrogen temperature programmed desorption