Effects of manganese oxide promoter on the CO and H-2 adsorption properties of titania-supported cobalt Fischer-Tropsch catalysts

Abstract

The adsorption properties of manganese-promoted Co/TiO2 Fischer-Tropsch (FT) catalysts were investigated by diffuse reflectance infrared spectroscopy (DRIFTS) using CO and H-2 as probe molecules. Manganese was found to be closely associated to the FT active Coo sites at the surface of the catalysts. With increased MnO loading, CO preferentially binded linearly to surface metal sites. Manganese also decreased the extent of Co-TiO2 interactions, increasing the Coo dispersion, resulting in higher H-2 chemisorption uptake. Furthermore, with increasing Moo loading, FT catalytic tests at 1 bar and 220 degrees C revealed an increase in C5+ selectivity and olefinic products. These findings suggest that MnO species induce both structural and electronic promotion effects, resulting in higher metal dispersions and lower hydrogenation activity of the catalyst, ultimately enhancing the overall FT catalytic performance. The findings also suggest that MnO catalyzes the water-gas shift reaction, thereby changing the syngas feed composition and affecting overall catalyst performance. (c) 2006 Elsevier Inc. All rights reserved.