Surface and reactor study of the effect of zinc on titania-supported Fischer–Tropsch cobalt catalysts Original Research Article

A series of Co/Zn/TiO2 catalysts have been synthesized and their Fischer–Tropsch (FT) activity studied. The effect of changing the sequence of impregnating zinc (5%) and cobalt (10%) onto the titania support as well as the effect of calcination of the catalyst in-between the impregnation steps have generated a range of new catalysts. Results obtained from XPS, AES and chemisorption (with hydrogen) techniques suggest that a ‘sandwich’ layer of zinc is formed in-between the cobalt and the titania even when the zinc was impregnated after the cobalt. The study reveals that Zn forms agglomerates on the TiO2 surface and that the Co sits on top of the non-crystalline Zn particles. The presence of zinc was found to have both beneficial as well as detrimental effects on Fischer–Tropsch activity that was determined by the amount of Zn added and the preparation procedures used to make the Co/Zn/TiO2 catalysts. Zinc was found to increase the dispersion of cobalt, but uncovered zinc particles were found to be active under the FT synthesis conditions forming mostly methane.