(559d) Investigation of Noble Metal Choice and Preparation Scale On Cobalt Fischer Tropsch Catalysts
AIChE Annual Meeting
Wednesday, November 10, 2010 - 4:18pm to 4:39pm
Previous studies have shown that the preparation method and pretreatment conditions affect dispersion, extent of reduction, location, and density of the Co and promoter species in Fisher-Tropsch (FT) catalysts.1 While the preparation method must produce highly active and selective cobalt FT catalysts, it also needs to satisfy the technical and economic requirements of scale-up to remain feasible. In this work, we investigate how the preparation scale and choice of expensive noble metal affect physicochemical and activity/selectivity properties of FT catalysts. Catalysts with dispersions of 10-20% at loadings of 20-25 wt% cobalt and 0-0.6 wt% noble metal (Pt, Re, Ru) on lanthanum-treated alumina were prepared on lab (5-20 g) and bench (50-200g) scales. In both preparation methods, the deposition of Co included three steps. Noble metal was deposited either in the 3rd Co deposition (co-deposition) or in a 4th deposition step (consecutive deposition). Characterization techniques, including hydrogen chemisorption, BET, H2-TPR, TEM, STEM, activity/selectivity tests in a fixed-bed reactor, XANES, and XAFS were used to study these catalysts.
Results and Discussion An analysis of the surface area, pore volume, and pore diameter suggests that the bench scale pellet procedures allow for more reproducible physical properties of the Co//La-Al2O3 catalysts than the lab scale technique. The catalysts in pellet form all have surfaces areas in the range of 99-105 m2/g, with pore volumes of 0.39-0.41 cm3/g, and average pore diameters of 14.9-15.0 nm. Hydrogen Temperature Programmed Reduction shows, consistent with trends from literature, that the noble metals promote the reduction by shifting the reduction peaks to lower temperatures.2 In addition, the co-deposited catalysts show more extreme reduction promotion than the consecutively deposited. Optimization of the reduction profile based on these results is currently being conducted to give a target dispersion and extent of reduction.
Insitu-XANES reduction and reaction show that the formation of Co metal sites cooresponds to Co FT catalyst activity. In addition, comparisons of XAFS on the noble metal edge give insight into bonding differences based on the scale of preparation and noble metal.3 The XANES and XAFS results were obtained at the J. Bennett Johnston Sr. Center for Advanced Microstructures and Devices (CAMD, Baton Rouge, LA) and Advanced Photon Source (Argonne National Lab, Argonne, IL).4
TEM imaging of the catalysts show Co particle sizes within the ideal range of 6-10 nm. The effects of the scale of preparation and noble metal choice on the average and standard deviation of the particle size are currently being investigated. STEM joined with XDS are being used to determine if the particles being measured are actually cobalt. In addition, STEM combined with XDS suggests a relationship between the noble metal and Co location.
Currently, fixed bed reactor runs are being performed. Preliminary results confirm FT activity for both lab and bench scale preparations. The significance of the preparation and noble metal variables are still being investigated.
Significance This study-in-progress is expected to provide insight into the influence of preparation scale and choice of noble metal on Co catalysts and develop an industrial procedure to prepare more economically viable catalysts for the FT synthesis.
References 1. Khodakov, A. Y.; Chu, W.; Fongarland, P. Chem. Rev. 2007, 107, (5), 1692-1744. 2. Bartholomew, C. H.; Farrauto, R. J. Fundamentals of Industrial Catalytic Processes, 2nd ed.; Wiley-Interscience: New Jersey, 2006, 65 3. B. Ravel, M. Newville, Athena, Artemis, Hephaestus: data analysis for X-ray absorption spectroscopy using IFEFFIT, J. Synchrotron Radiat. (2005) 537. 4. Use of the Advanced Photon Source at Argonne National Laboratory was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.