Effect of Silver and Manganese Promoters on Performance of Cobalt Fischer-Tropsch Catalysts
Fischer-Tropsch (FT) Synthesis (FTS) based fuels have no sulfur content, high cetane number and fewer aromatic compounds in comparison to common petroleum-derived fuels. These unique characteristics make FTS the best choice for providing the future need of hydrocarbon fuels. Supported cobalt is a commercial catalyst for FTS. Many ongoing research efforts aim to enhance the cobalt FTS catalytic performance. Incorporating different metal oxides as promoters is one promising way to increase the cobalt catalytic characteristics. Noble metals are commonly used as a promoter for FTS catalyst. They enhance the catalytic performance by forming an over layer over Co particles after catalyst activation.1 This layer facilitates the reduction by H2 dissociation and spillover mechanism.2 However, some other metals have been proposed as substitutes for noble metals due to their relatively high cost. Silver is a relatively low-priced metal with comparable reduction promotion effects and even better selectivity compared to Pt.3 Additionally, many researchers have investigated Mn as a possible promoter for the FTS process. Mn enhances the catalyst activity and selectivity, but attenuates the catalyst reducibility.4 However, studies show that incorporation of Pt group noble metals and Mn in combination results in higher selectivity (C5+) without any loss in reducibility,5but using noble metals result in increased catalyst price. This study compares effects of silver, as relatively low-priced metal, with Mn in combination as potential substitutes for Ru and Pt on silica stabilized alumina supported Co FT catalysts.
1. Xin, H. L.; Alayoglu, S.; Tao, R.; Genc, A.; Wang, C.-M.; Kovarik, L.; Stach, E. A.; Wang, L.-W.; Salmeron, M.; Somorjai, G. A., Revealing the Atomic Restructuring of Pt–Co Nanoparticles. Nano letters 2014, 14(6), 3203-3207.
2. Jacobs, G.; Chaney, J. A.; Patterson, P. M.; Das, T. K.; Maillot, J. C.; Davis, B. H., Fischer-Tropsch synthesis: study of the promotion of Pt on the reduction property of Co/Al2O3 catalysts by in situ EXAFS of Co K and Pt LIII edges and XPS. Journal of Synchrotron Radiation 2004, 11(5), 414-422.
3. Jermwongratanachai, T.; Jacobs, G.; Ma, W.; Shafer, W. D.; Gnanamani, M. K.; Gao, P.; Kitiyanan, B.; Davis, B. H.; Klettlinger, J. L.; Yen, C. H., Fischer–Tropsch synthesis: Comparisons between Pt and Ag promoted Co/Al2O3 catalysts for reducibility, local atomic structure, catalytic activity, and oxidation–reduction (OR) cycles. Applied Catalysis A: General 2013,464, 165-180.
4. Werner, S.; Johnson, G. R.; Bell, A. T., Synthesis and Characterization of Supported Cobalt–Manganese Nanoparticles as Model Catalysts for Fischer–Tropsch Synthesis. ChemCatChem2014, 6 (10), 2881-2888.
5. (a) Martı́nez, A. n.; López, C.; Márquez, F.; Dı́az, I., Fischer–Tropsch synthesis of hydrocarbons over mesoporous Co/SBA-15 catalysts: the influence of metal loading, cobalt precursor, and promoters. Journal of Catalysis 2003, 220 (2), 486-499; (b) den Breejen, J. P.; Frey, A. M.; Yang, J.; Holmen, A.; van Schooneveld, M. M.; de Groot, F. M.; Stephan, O.; Bitter, J. H.; de Jong, K. P., A highly active and selective manganese oxide promoted cobalt-on-silica Fischer–Tropsch catalyst. Topics in Catalysis 2011, 54 (13-15), 768-777.