Noble Metal Catalysts for the Hydrocracking of Fischer-Tropsch waxes

Abstract: Fischer-Tropsch synthesis enables the production of high quality diesel fuel from biomass derived synthesis gas. In order to increase the overall diesel yield, it is necessary to perform a subsequent hydrocracking of the long-chain linear paraffins. This work is focused on characterization and testing of catalysts for the hydrocracking reaction of Fischer-Tropsch waxes. In particular, noble metal catalyst based on Pt and Pd on amorphous silica-alumina support were tested. Palladium based catalysts performed nearly an ideal bifunctional mechanism, while platinum based catalysts performed another way of cracking: hydrogenolysis. Platinum based catalysts are more active than palladium ones, with the same metal loading. This is a consequence of the nature of the metal sites. The product distribution is similar for both platinum and palladium catalysts. However, due to the hydrogenolysis cracking mechanism performed by platinum based catalysts, the amount of light gases produced on platinum based catalysts is higher. Furthermore, the deactivation behavior of the Platinum and Palladium catalysts has been studied, and the results showed that the dispersion of the active phase decreased with deactivation and the average crystallite diameter increased. This means a decrease in activity. A regeneration program, temperature programmed oxidation (TPO), has been carried out demonstrating that the activity was not completely recovered.