Titania-Decorated Silicon Carbide-Containing Cobalt Catalyst for Fischer-Tropsch Synthesis Yuefeng Liu,* ,† Benoit de Tymowski, † Fabrice Vigneron, † Ileana Florea, ‡ Ovidiu Ersen, ‡ Christian Meny, ‡ Patrick Nguyen, § Charlotte Pham, § Francis Luck, ⊥ and Cuong Pham-Huu* ,† † Laboratoire des Mate ́ riaux, Surfaces et Proce ́ de ́ s pour la Catalyse (LMSPC), UMR 7515, CNRS-Universite ́ de Strasbourg (UdS), 25, rue Becquerel, 67087 Strasbourg Cedex 08, France ‡ Institut de Physique et Chimie des Mate ́ riaux de Strasbourg (IPCMS), UMR 7504, CNRS-Universite ́ de Strasbourg (UdS), 23, rue du Loess, 67034 Strasbourg Cedex 02, France § SICAT/ACM Technical Center, Industriestrasse 1, D-77731 Willstä tt, Germany ⊥ Total, Direction Ge ́ ne ́ rale-Direction Scientifique, 24 cours Michelet, F-92069 Paris La De ́ fense Cedex, France * S Supporting Information ABSTRACT: The metal-support interactions of titanium dioxide decorated silicon carbide (β-SiC)-supported cobalt catalyst for Fischer-Tropsch synthesis (FTS) were explored by a combination of energy-filtered transmission electron microscopy (EFTEM), 59 Co zero-field nuclear magnetic resonance ( 59 Co NMR), and other conventional character- ization techniques. From the 2D elemental maps deduced by 2D EFTEM and 59 Co NMR analyses, it can be concluded that the nanoscale introduction of the TiO 2 into the β-SiC matrix significantly enhances the formation of small and medium- sized cobalt particles. The results revealed that the proper metal-support interaction between cobalt nanoparticles and TiO 2 led to the formation of smaller cobalt particles (<15 nm), which possess a large fraction of surface atoms and, thus, significantly contribute to the great enhancement of conversion and the reaction rate. The cobalt time yield of the catalyst after modification increased to 7.5 × 10 -5 mol CO g Co -1 s -1 at 230 °C, whereas the C 5+ selectivity maintained a high level (>90%). In addition, the adequate meso- and macro-pores of the SiC-based support facilitated intimate contact between the reactants and active sites and also accelerated the evacuation of the intermediate products. It was also worth noting that a superior and stable FTS specific rate of 0.56 g C 5+ g catalyst -1 h -1 together with high C 5+ selectivity of 91% were obtained at common industrial content of 30 wt % cobalt. KEYWORDS: metal-support interaction, Fischer-Tropsch synthesis, silicon carbide, cobalt, titanium oxide, energy-filtered TEM, 59 Co NMR, catalysis 1. INTRODUCTION Fischer-Tropsch synthesis (FTS) is a key technology in the more global gas-to-liquids (GTL) process, which allows the transformation of synthesis gas (2H 2 + CO), issued from natural gas reforming into liquid hydrocarbons, followed by hydrocracking of the heavy fraction into useful compounds, such as naphtha, diesel, lubricants, and others. 1-6 The most employed active phase for the low-temperature FTS process is supported cobalt, either pure or doped with trace amounts of noble metal to enhance the reduction of the active phase and to improve the dispersion of metal particles. 7-11 Cobalt presents several advantages, such as high stability, high activity for liquid hydrocarbons formation and low selectivity toward oxygenated products, resistance to oxidation, low water-gas shift (WGS) tendency, and acceptable price for industrial development. However, the high activity of the cobalt phase also leads to an extremely high sensitivity of the catalyst selectivity to the reaction temperature. Cobalt active phase is typically employed in a supported form for the FTS process. The support should display a relatively high specific surface area to achieve a high dispersion of the metal particles, good mechanical and hydrothermal resistance, and a medium level of metal-support interaction to allow complete reduction of the active phase and to prevent sintering of the cobalt. The most employed supports for the FTS are alumina; silica; titania; and carbon-based materials, such as activated carbon, carbon nanotubes, and nanofibers. 12-19 Among these supports, alumina, either pure or promoted, is the most employed as a support for commercial catalysts. However, on traditional supports such as alumina and silica, it is difficult to reduce small particles of metal oxide Received: November 11, 2012 Revised: January 17, 2013 Published: January 22, 2013 Research Article pubs.acs.org/acscatalysis © 2013 American Chemical Society 393 dx.doi.org/10.1021/cs300729p | ACS Catal. 2013, 3, 393-404