Effect of magnesia on alumina-supported cobalt Fischer-Tropsch synthesis catalysts

A series of magnesia-modified alumina-supported cobalt catalysts were prepared with it two-step impregnation method using the incipient wetness technique. N, physisorption, X-ray diffraction (XRD). laser Raman spectroscopy (LRS), X-ray photoelectron spectroscopy (XPS), H-2 temperature-programmed reduction (H-2-TPR). H-2 temperature-programmed desorption (H-2-TPD) and oxygen titration were used for the characterization of the catalysts. A cobalt surface phase, which has strong interaction with the support, was detected by XPS, and its, content decreased with introduction of the magnesia into the catalysts. indicating, that Mg modification can inhibit the interaction between the cobalt oxide and the support. However, large amounts of magnesia caused a decrease in the catalysts reducibility due to the formation of MgO-CoO solid solution. Small amounts of magnesia were found to improve the activity of cobalt catalysts for Fischer-Tropsch synthesis but larger amounts of magnesia decreased the activity, and the methane and CO, selectivity increased for all the magnesia-modi tied catalysts furthermore, the olefin to paraffin ratio increased with ail increase in magnesia content, These observed effects of magnesia on the catalytic performance of cobalt catalysts could deduce from poor reducibility of higher magnesia content catalysts and/or magnesia content-dependent catalyst surface reconstruction suppression. (c) 2005 Elsevier B.V. All rights reserved.