(611f) Comparison of Cobalt Fischer-Tropsch Catalysts on Robust Silica-Alumina Supports

Authors: 
Rahmati, M., Brigham young university
Argyle, M. D., Brigham Young University
Hecker, W. C., Brigham Young University
Safdari, M. S., Chemical Engineering Department, Brigham Young University, Provo, UT 84602, USA
Fischer-Tropsch Synthesis (FTS) is a key step in gas-to-liquid processes to produce clean and environmentally friendly fuels. The Fischer-Tropsch (FT) reaction is catalyzed, typically by supported cobalt catalysts. The supportâ??s physical properties, including pore size and thermal stability, and chemical characteristics, like surface acidity, can greatly affect the catalystâ??s performance [1, 2]. Recently, we have developed a new support which is simple to prepare and has unique characteristics, including high surface area and pore volume, very high thermal stability, and low surface acidity [3]. This bicomponent support, AlSi, containing 95 wt% alumina and 5 wt% silica, has previously been incorporated into successful supported iron FT catalysts [4]. The goal of this research is to compare the performance of cobalt FT catalysts using AlSi versus other commonly used alumina supports, including those available commercially from Sasol and St. Gobein. To focus only on the support effects, all of the catalysts were synthesized using the same incipient wetness impregnation method, with 20 wt% cobalt and 0.15 wt% ruthenium as a reduction promoter. Each catalyst was characterized by TPO, TPR, XRD, TEM, BET, EOR, and CO and H2 uptake experiments to compare the nanostructure and other physical and chemical features of the catalysts. Catalytic activity, selectivity, and stability were investigated in a packed bed reactor operated at industrial FTS conditions (220°C and 20 atm at a 2.1:1 H2/CO ratio) during 240 h runs. XRD data show that with calcination to temperatures even higher than 1100°C, the AlSi support still consists of predominantly the gamma phase, which allows the support to maintain high surface area (>95 m2/g). Further, this thermal stability allows high temperature oxidative treatments to remove surface acid sites, which appears to produce supports that favor increased FT reaction rates and improved C2+ selectivity. Nitrogen physisorption data also indicate that the AlSi surface area and pore volume are relatively high, about 3 times more than commercially available Sasol alumina-silica supports, which provide better selectivity and activity.

1. Khodakov, A.Y., Fischer-Tropsch synthesis: Relations between structure of cobalt catalysts and their catalytic performance. Catalysis Today, 2009. 144(3â??4): 251-257.

2. Soled, S.L., et al., Control of Metal Dispersion and Structure by Changes in the Solid-State Chemistry of Supported Cobalt Fischerâ??Tropsch Catalysts. Topics in Catalysis. 26(1): 101-109.

3. Mardkhe, M.K., et al., Acid site properties of thermally stable, silica-doped alumina as a function of silica/alumina ratio and calcination temperature. Applied Catalysis A: General, 2014. 482: 16-23.

4. Keyvanloo, K., et al., Supported Iron Fischerâ??Tropsch Catalyst: Superior Activity and Stability Using a Thermally Stable Silica-Doped Alumina Support. ACS Catalysis, 2014. 4(4): 1071-1077.

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