Iron and cobalt Fischer-Tropsch catalysts prepared by the solvated metal-atom technique

The synthesis of hydrocarbons from catalytic hydrogenation of carbon monoxide was investigated over Co/Al2O3 and Co/NaX catalysts at 1 atm, 493–553 K, H2/CO = 2, and gas hourly space velocity (GHSV) = 1200. These catalysts were characterized by hydrogen chemisorption. X-ray diffraction (XRD), and temperature-programmed reduction. The type of support had pronounced effects on the activity and selectivity of cobalt. The results indicated that the cobalt oxide supported on alumina is easier to reduce than that on zeolite X. This is essentially due to strong acidity of the HX and the high dispersion of cobalt. This would result in less active sites for the chemisorption of hydrogen, and would result in a decrease in activity and an increase in the selectivity to alkenes. Significant amounts of 2-butene are observed on Co/NaX catalyst, indicating that the predominant secondary reaction is isomerization rather than oligomerization and cracking reactions. The presence of water in the zeolite may cause a change in the catalytic behavior of the Co/NaX catalyst. The kinetic order of the reaction for Co/Al2O3 is negative to the carbon monoxide partial pressure and positive to the hydrogen partial pressure. The reaction rates for the Co/NaX catalysts are independent of the carbon monoxide partial pressure and become more strongly dependent on the hydrogen partial pressure with positive order. The different kinetics seem to be due to different reaction mechanisms operative on the cobalt surface with different degrees of reduction.