Particle size effects in Fischer-Tropsch synthesis by cobalt.pdf

PZ D a A R R A A K P F C M O 1 s a a o m ( p u e r b a t g i o g t s 1 o [ 0 dCatalysis Today 181 (2012) 75– 81 Contents lists available at ScienceDirect Catalysis Today jou rn al h om epage: www.elsev ier .com/ locate /ca t tod article size effects in Fischer–Tropsch synthesis by cobalt hou-jun Wang, Stephanie Skiles, Fan Yang, Zhen Yan, D. Wayne Goodman ? epartment of Chemistry, Texas AM University, College Station, TX 77843, USA r t i c l e i n f o rticle history: eceived 11 March 2011 eceived in revised form 2 June 2011 ccepted 27 June 2011 vailable online 28 July 2011 a b s t r a c t In order to study the intrinsic particle size effect of Co catalysts in Fischer–Tropsch (FT) synthesis, a series of Co/SiO2 model catalysts with various metal coverages (0.25–6.0 ML), corresponding to sizes in the range of 1.4–10.5 nm were prepared in an ultrahigh vacuum chamber and tested at 513 K under atmospheric pressure in a batch reactor. The Co particle size distribution and the number of active sites were estimated from the TEM images. Kinetic data and post-reaction XPS spectra showed that for the small Co particleseywords: article size T o/SiO2 catalyst odel catalyst xidation (1.4–2.5 nm), the Co surface was readily oxidized by water vapor, while for the relatively large Co particles (3.5–10.5 nm), such oxidation was not evident. The oxidation for the small Co particles leads to lower TOF and higher CH4 selectivity, while both reactivity and selectivity were relatively constant for the relatively large Co particles. The lack of intrinsic particle size effect for the metallic Co particles in the range of 3.5–10.5 nm is consistent with structure insensitivity in FT synthesis. ? 2011 Elsevier B.V. All rights reserved.. Introduction In history, two general approaches have evolved to produce ubstitutes for naturally