Friday, November 12, 2010: 8:51 AM
251 C Room (Salt Palace Convention Center)
The physical and surface chemistry properties of four activated carbons (ACs) have been studied, and the effects of these properties on the distribution and reduction of metal precursors of Fischer-Tropsch (FT) catalysts have been noted. The four ACs used have been derived from peat, generic wood, pecan and walnut. The catalysts used are Fe with Mo-Cu-K additives, supported on the various ACs, successfully used earlier for selective production of C1-C34 hydrocarbons. Characterization techniques used include BET, SEM and EDS, surface pH, TPD-MS, TEM and TPR. Analyzing the BET, TPD and TEM results of the four carbon-supported Fe-Mo-Cu-K catalysts shows that metal precursors are uniformly distributed on each AC surface, but the distribution of metal precursors on carbon surface is likely related to pore types and amounts, and not with the total surface area of supports. For the wood-based AC, which contains greater amounts of micropores, more metal precursors tend to be present on the exterior surface, and the average metal particle size is also larger. The TPR and BET results indicate that the interaction between metallic precursors and AC surface appears to be associated with both the chemical nature of the AC support and size of metal precursors. TPR and TPD indicate that stronger interactions between metal precursors and supports are observed on the peat-based ACs, with more neutral or basic oxygen-containing groups, and smaller metal sizes, and the weakest interactions on the wood-based AC support. The large particles on the exterior of the wood-based AC surface likely weaken the interaction. All four catalysts were used in FT reactions. The relationships between the performance of the catalyst in the FT reaction and AC type are discussed. The FTS activity can be related directly to the BET parameters associated with the relative ease of mass transfer and the relative fraction of metal crystallites present in the wide pores, and inversely to the metal crystallite size. The selectivity towards C5+ products is related to the amount of species evolved during the TPR of the AC support, primarily the number of basic and neutral species on the surface. High selectivity towards C1 correlates well to low pH of the external surface of the support.