Cobalt Fischer Tropsch Synthesis Research Articles

Effect of Cobalt Precursors on the Dispersion of Cobalt on MCM-41

Co/MCM-41 catalysts were prepared using the incipient wetness impregnation technique with aqueous solutions of different cobalt compounds such as cobalt nitrate, cobalt chloride, cobalt acetate, and cobalt acetylacetonate. MCM-41 is known to have a restricted pore structure; however, using organic precursors such as cobalt acetate and cobalt acetylacetonate resulted in very small cobalt oxide particles that could not be detected by XRD even for a cobalt loading as high as 8 wt%. These cobalt particles were small enough to fit into the pores of MCM-41. However, they were found to chemisorb CO in only relatively small amounts and to have low activities for CO hydrogenation—probably due to the formation of cobalt silicates. The use of cobalt chloride resulted in very large cobalt particles/clusters and/or residual Cl--blocking active sites, and, consequently, very small active surface area was measurable. The use of cobalt nitrate resulted in a number of small cobalt particles dispersed throughout MCM-41 and some larger particles located on the external surface of MCM-41. Cobalt nitrate appeared to be the best precursor for preparing high-activity MCM-41-supported cobalt Fischer–Tropsch synthesis catalysts.

CO and CO 2 hydrogenation study on supported cobalt Fischer–Tropsch synthesis catalysts

The conversion of CO/H 2, CO 2/H 2 and (CO+CO 2)/H 2 mixtures using cobalt catalysts under typical Fischer–Tropsch synthesis conditions has been carried out. The results show that in the presence of CO, CO 2 hydrogenation is slow. For the cases of only CO or only CO 2 hydrogenation, similar catalytic activities were obtained but the selectivities were very different. For CO hydrogenation, normal Fischer–Tropsch synthesis product distributions were observed with an α of about 0.80; in contrast, the CO 2 hydrogenation products contained about 70% or more of methane. Thus, CO 2 and CO hydrogenation appears to follow different reaction pathways. The catalyst deactivates more rapidly for the conversion of CO than for CO 2 even though the H 2O/H 2 ratio is at least two times larger for the conversion of CO 2. Since the catalyst ages more slowly in the presence of the higher H 2O/H 2 conditions, it is concluded that water alone does not account for the deactivation and that there is a deactivation pathway that involves the assistance of CO.