Effects of Confinement in Carbon Nanotubes on the Performance and Lifetime of Fischer-Tropsch Iron Nano Catalysts

Document Type: Research Article

Authors

1 Faculty of Chemistry, University of Tehran, Tehran, I.R. IRAN

2 Research Institute of Petroleum Industry, Tehran, I.R. IRAN

Abstract

The effects of confinement in carbon nanotubes on Fischer-Tropsch (FT) activity, selectivity and lifetime of Carbon NanoTubes (CNTs) supported iron catalysts are reported. A method was developed to control the position of the catalytic sites on either inner or outer surface of carbon nanotubes. TEM analyses revealed that more than 80% of iron oxide particles can be controlled to be positioned at inner or outer surface of the nanotubes. Deposition of iron oxide inside the nanotube pores decreased the average size of the iron oxide particles from 14 to 7 nm and shifted the reduction peak temperature of iron oxide species to lower temperatures (from 389 to 371oC , 428 to 413oC and 580 to 530oC) and improved the reducibility of the catalyst by 25%. Catalytic performances of the catalysts in terms of FT experiment were tested in a fixed-bed micro reactor; the catalyst with catalytic sites inside the pores showed 23% higher initial activity than the catalyst with catalytic sites outside the pores. Also, the catalyst with catalytic sites inside the pores exhibited higher selectivity to heavier hydrocarbons (40.5% vs. 32.9% C‌5+ selectivity). In addition, deposition of catalytic sites on interior surface of the nanotubes resulted in a more stable catalyst, while its counterpart experienced 46.4% deactivation within a period of 720 h due to catalytic sites sintering. It is concluded that encapsulation of the catalytic nanoparticles inside the nanotubes prevents the catalytic site agglomeration.

Keywords

Main Subjects


[1] AndersonR.B., “The Fischer-Tropsch Synthesis”,Orlando,FL: Academic Press, (1984).
[2] Dry M.E., The Fischer-Tropsch Synthesis, Catal. Scie. and Tech., 1, p. 159 (1981).
[3] Bartholomew C.H.,New Trends in CO Activation, Stud. in Surf. Scie. and Catal., 64, p. 158 (1991).
[4] Bukur D.B., Lang X., Mukesh D., Zimmerman W.H., Rosynek M.P., Li C., Development of Improved Fischer-Tropsch Catalyst, Ind. Eng. Chem. Res., 29, p. 1588 (1990).
[5] Malek Abbaslou R.M., Tavasoli A., Dalai A.K., Iron Catalysts Supported on Carbon Nanotubes for Fischer-Fropsch Synthesis Effect of Catalytic Site Position, Appl. Catal. A: Gen., 367, p. 47 (2009).
[6] Tavasoli A., Sadagiani K., Khorashe F., Seifkordi A.A., Rohani A.A., Nakhaeipour A., Cobalt Supported on Carbon Nanotubes-A Promising Novel Fischer-Tropsch Synthesis Catalyst, Fuel Proc. Technol., 89, p. 491 (2007).
[7] Tavasoli A., Rashidi A.M., Sadaghiani K., Karimi A., Khodadadi A., Mortazavi Y., "Carbon Nanotubes Supported Cobalt Catalyst for Converting Synthesis Gas Into Hydrocarbons", European Patent EP1782885 (2005).
[8] Tavasoli A., Sadaghiani K., Nakhaeipour A., Ghalbi Ahangari M., Cobalt Loading Effects on the Structure and Activity for Fischer-Tropsch and Water-Gas Shift Reaction of Co/Al2O3 Catalysts, Iran. J. Chem. Chem. Eng., 26, p. 9 (2007).
[9] Ma W., Kugler E.L., Wright J., Dadyburjor D.B.,Mo-Fe Catalysts Supported on Activated Carton for Synthesis of Liquid Fuels by the Fischer-Tropsch Process: Effect of Mo Addition on Reducibility, Activity and Hydrocarbon Selectivity, Energy Fuels, 20, p. 2299 (2006).
[10] Guczi L., Stefler G., Geszti O., Koppány Zs., Kónya Z., Molnár É., Urbánc M., Kiricsi I., CO Hydrogenation over Cobalt and Iron Catalysts Support over Multi wall Carbon Nanotubes: Effect of Preparation, J. Catal., 244, p. 24 (2006).
[11] Bahome M.C., Jewell L.L., Padayachy K., Hildebrandt D., Glasser D., Datye A. K., Coville N. J., Fe-Ru Small Particle Bimetallic Catalysts Supported on Carbon Nanotubes for Use in Fischer-Tropsch Synthesis, Appl. Catal. A: Gen., 328, p. 243 (2007).
[12] Van Steen E., Prinsloo F.F., Some Evidence Refuting the Alkenyl Mechanism for Chain Growth in Iron-Based Fischer-Tropsch Synthesis, Catal. Tod., 71, p. 327 (2002).
[13] Bahome M.C., Jewell L.L., Hildebrandt D., Glasser D., Coville N. J., Fischer-Tropsch Synthesis over Iron Catalysts Supported on Carbon Nanotubes, Appl. Catal. A: Gen., 287, p. 60 (2005).
[14] Chen W., Pan X., Bao X., Tuning of Redux Properties of Iron and Iron Oxides via Encapsulation within Carbon Nanotubes, Chem. Soc., 129, p. 7421 (2007).
[15] Pan X., Fan Z., Chen W., Ding Y., Luo H., Bao A.N.D.X., Enhanced Ethanol Production Inside Carbon-Nanotube Reactors Containing Catalytic Particles, Nature, 6, p. 507 (2007).
[16] Menon M., Andriotis A.N., Froudakis G.E., Curvature Dependence of the Metal Catalyst Atom Interaction with Carbon Nanotubes Walls, Phys. Lett., 320, p. 425 (2000).
[17] Santiso E.E., Adsorption and Catalysis: The Effect of Confinement on Chemical Reaction, Appl. Surf. Sci., 252, p. 766 (2005).
[18] Granqvist C.G., Buhrman R.A.,Sintering Behavior of Nickel Particles Supported on Alumina Model Catalyst in Hydrogen Atomosphere, J. Catal., 42, p. 477 (1976).
[19] Sehested J., Carlsson A., Janssens T.V.W., Hansen P.L., Datyey A.K., Sintering of Nickel Steam-Reforming Catalysts on MgAl2O4 Spinel Supports, J. Catal., 197, p. 200 (2001).
[20] Joo S.H., Choi S.J., Oh I., Kwak J., Liu Z., Terasaki O., Ryoo R., Ordered Nanoporous Arrays of Carbon Supporting High Dispersions of Platinum Nanoparticles, Nature, 412, p. 169 (2001).
[21] Davis B. H., Fischer-Tropsch Synthesis: Comparison of Performances of Iron and Cobalt Catalysts, Ind. Eng. Chem. Res., 46, p. 8938 (2007),
[22] Bartholomew C.H., Mechanisms of Catalyst Deactivation, Appl. Catal. A: Gen., 212, p. 17 (2001).