COBALT HZSM-5 ZEOLITE CATALYST FOR THE CONVERSION OF SYNGAS TO HYDROCARBONS

Physical and chemical properties as well as the activity and selectivity of Co/HZSM-5 zeolite bifunctional catalyst have been studied for conversion of synthesis gas. These catalysts were prepared by incipient wetness impregnation with different conditions of drying, calcination and reduction. The cobalt content in the catalyst and the effect of thoria, as promoter, were also studied. The catalysts prepared were characterized and tested in a fixed bed continuous reactor system. The results show that drying is the most important step in the preparation, having more active catalysts with fast drying conditions, probably due to the formation of smaller cobalt particles. The interaction between the metal and the zeolite surface seems to contribute significantly to the catalyst activity. Maximum activity of the catalyst is obtained with 1.5 wt.-% of thorium, resulting in an increase of C6+ selectivity. This is explained in terms of a shift in chemisorption properties of the catalyst. The basic character of the promoter affects the zeolite acidity, decreasing the aromatic proportion in the liquid hydrocarbon fraction. Finally, the bifunctional catalyst selected in this study is compared with a physical mixture of a commercial Fischer-Tropsch catalyst and HZSM-5 zeolite.