Cobalt catalysts on carbon-based materials for Fischer-Tropsch synthesis: a review

Abstract

Highlights Challenges and opportunities in Co/C catalyzed Fischer-Tropsch synthesis  Guidelines for the design of Co/C catalysts for Fischer-Tropsch synthesis  The choice of carbon materials as Fischer-Tropsch synthesis support is rationalized  The evolution of TOF and SC5+ with Co particle size is relatively complex  Effect of confinement and spillover on catalyst performances are discussed

Beyond confinement effects in Fischer-Tropsch Co/CNT catalysts

“…Oxide supports such as SiO 2 , Al 2 O 3 or TiO 2 are generally employed to stabilize cobalt particles, but they present the drawback of undesirable strong cobalt-support interactions that lead to the formation of non-reducible and inactive mixed metal oxides [4]. Such detrimental interactions can be circumvented by using carbon materials as support modifier [6,7] or directly as support [8], since their interaction with cobalt is weaker, which facilitates metal reduction. Additionally, the good thermal conductivity of some sp 2 carbon materials, such as carbon nanotubes (CNT) enables to limit methane formation and catalyst deactivation, by avoiding the formation of hot spots resulting from the high exothermicity of the FT reaction.…”

“…The principal identified Co/C catalyst features influencing the catalyst performances are: i) the Co particle size; ii) the Co reducibility; iii) the cobalt phase (fcc or hcp); and iv) the confinement of cobalt particles (particularly in CNT) [8]. Recently, we also reported that hydrogen spillover from the cobalt particles to the carbon support can also contribute to the enhancement of Co/C catalytic activity [9].…”

“…Among the different methods for Co/C catalyst preparation, the incipient wetness impregnation (IWI) is by far the most popular since: i) it is relatively fast and inexpensive, and ii) small particle size and narrow particle distribution are usually obtained. Among the different carbon supports investigated for FTS, oxidized CNT have been particularly studied since they offer the additional possibility of confinement of the active phase [8,10]. Furthermore, it was demonstrated that oxidized CNT show catalytic activity towards CO hydro-deoxygenation reaction to yield long chain hydrocarbons similar to FTS [11].…”

“…Another important parameter to consider during catalyst preparation is the choice of the cobalt precursor and of the impregnating solvent. The decomposition of the cobalt precursor is a crucial step in Co-based catalyst preparation, and a slow decomposition rate favors small Co particle size [8]. Cobalt acetate and cobalt nitrate precursors are the most commonly used.…”

“…Additionally, the solvent used during the catalyst preparation allows not only dissolving the precursor and promoting its contact with the support, but also controlling the final catalyst structure. The interaction between the cobalt precursor and the support depends on the solvent surface tension, which controls support wettability [8]. De Jong and coworkers compared water and ethanol as solvents for the impregnation of CNT with cobalt nitrate [14].…”