FISCHER-TROPSCH SYNTHESIS ON COBALT AND RUTHENIUM - METAL DISPERSION AND SUPPORT EFFECTS ON REACTION-RATE AND SELECTIVITY

Metal dispersion and support effects on Fischer-Tropsch synthesis rate and selectivity were studied at conditions that favor the information of C5+ hydrocarbons (> 80% selectivity). On Ru, these effects are minor for the supports (SiO2, Al2O3, TiO2) and the dispersion range (0.0009-0.60) tested. Site-time yields are similar (1.25-1.95 × 10-2 s-1) on all Ru catalysts (476 K, 560 kPa, H2/CO = 2.1). On Co, hydrocarbon synthesis rates are also proportional to metal dispersion (0.0045-0.095) and independent of the metal oxide support (SiO2, Al2O3, TiO2, and ZrO2-modified SiO2 and TiO2). Site-time yields (1.6-3.0 × 10-2 s-1) are independent of Co dispersion and support (473 K, 2000 kPa, H2/CO = 2.1). Dispersion and support influence C5+ selectivity slightly on both Co and Ru catalysts; these changes reflect transport-enhanced secondary reactions and not modifications of intrinsic chain growth kinetics. Specifically, transport restrictions imposed by the physical structure of the support and by a high site density within catalyst pellets increase the residence time and the readsorption probability of reactive a-olefins and lead to higher C5+ yields and more paraffinic products. © 1992.