Hydrogen Spillover in the Fischer‐Tropsch Synthesis on Carbon‐supported Cobalt Catalysts

Abstract

The Fischer‐Tropsch reaction transforms syngas into high added value products, among which liquid fuels. Numerous parameters determine catalytic activity and selectivity towards the most desired hydrocarbons. The performances of cobalt‐based catalysts used in the reaction are known to depend critically on Co particle size and crystallographic phase. Here, we present a comparative study of Co‐based catalysts supported on three carbon supports: multi‐wall carbon nanotubes, carbon nanofibers and a fibrous material. Our results show that, while the selectivity towards C5+ follows the expected tendency with respect to Co particle size, this is not the case for the TOF. These results can be rationalized considering that the amount of H2 uptake on each catalyst increases with oxygen and defect concentration on the support. The catalyst on the support presenting many edges and oxygen surface groups, necessary for H2 spillover, presents the highest activity. Furthermore, the hydrogen spillover contributes to the enhancement of olefin hydrogenation and methane production.

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

“…Additionally, the spilled-over species formed on the metal may react with reactant adsorbed on the support, which could modify or promote the catalytic activity and selectivity [28]. In FTS, hydrogen spillover has been studied for cobalt catalysts supported on metal oxides [137,138], and on carbon [139,140]. In the case of metal oxides, hydrogen spillover allowed explaining the role of noble metals (Pt, Au) as promoters for Co reduction in Co/Al2O3 catalysts [137,138].…”

“…In the case of metal oxides, hydrogen spillover allowed explaining the role of noble metals (Pt, Au) as promoters for Co reduction in Co/Al2O3 catalysts [137,138]. In the case of carbon-based supports, many factors can promote hydrogen spillover [139]. The capacity of a carbon support to reversibly store atomic H relies on a number of factors such as accessible surface area, geometric nanostructure, defects, dopants, surface chemistry, surface coverage and the interaction of metal particles and support [139,141].…”

“…In the case of carbon-based supports, many factors can promote hydrogen spillover [139]. The capacity of a carbon support to reversibly store atomic H relies on a number of factors such as accessible surface area, geometric nanostructure, defects, dopants, surface chemistry, surface coverage and the interaction of metal particles and support [139,141]. Phaahlamohlaka et al [140] studied the effects of hydrogen spillover on Co catalysts prepared from mesoporous hollow carbon spheres (MHCS) with cobalt loading of 15wt.% and different nominal Ru loadings (0.2wt.% Ru-Co/MHCS and 0.5wt.% Ru-Co/MHCS) [140].…”

“…In FTS (T = 220°C, P = 10 bar, H2/CO = 2, GHSV = 1800mL g -1 h -1 ), the high activity of CoRu/MHCS catalyst was attributed to the primary hydrogen spillover, while no accurate explanation was identified for its low SC5+. In order to provide an answer to this question, the direct involvement of hydrogen spillover on FTS activity and selectivity on non-promoted carbon-supported cobalt catalysts was recently demonstrated for the first time [139]. As mentioned above, the carbon support properties seem to influence the occurrence of Hspillover.…”

Carbon-based catalysts for Fischer–Tropsch synthesis

“…Cobalt catalysts were prepared using three kinds of carbon supports of CNTs, CNFs, and fibrous material (FM). 104 The FM support demonstrated a relatively large surface area with more surface oxygen groups and defects, which favored the formation of small cobalt particles with more significant hydrogen uptake. Hydrogen spillover was promoted by the surface oxygen groups and defects on the support.…”