Effects of Co and Ru Intimacy in Fischer–Tropsch Catalysts Using Hollow Carbon Sphere Supports: Assessment of the Hydrogen Spillover Processes

Abstract

Mesoporous hollow carbon spheres (MHCSs) were synthesized (d = 290 nm; carbon shell 20−35 nm), and their hollow morphology was exploited to study the influence of Ru nanoparticle location relative to Co3O4 nanoparticles on the reduction behavior and activity of Co Fischer−Tropsch catalysts. Ru nanoparticles were loaded both inside and outside the MHCS, while Co3O4 particles (ca. Co 15 wt % loading) were loaded on the outside of the MHCS. The use of in situ powder X-ray diff raction (PXRD) and temperaturepro-grammed reduction studies on the catalysts indicated the eff ect of Ru location on the Co3O4 reduction pathways. A secondary hydrogen spillover eff ect was invoked to explain a complete reduction of the Co3O4 on Ru@MHCS@Co at 450 °C. Secondary hydrogen spillover enhanced the CoO to Co transformation by lowering the reduction temperature when compared to the unpromoted catalyst. Primary hydrogen spillover was inferred to explain the complete reduction of Co3O4 to Co metal on CoRu/MHCS at 300 °C. After catalyst activation at 350 °C, the primary spillover process yielded a catalyst with higher Fischer−Tropsch activity (ca. 2×) than the unpromoted catalyst and the catalysts where Ru and Co were separated by the mesoporous carbon shell. This was partially related to the Co phases that formed on the carbon support during reduction and the catalyst degree of reduction that was reliant on the type of hydrogen spillover process.

Morphology Evolution of Hcp Cobalt Nanoparticles Induced by Ru Promoter

“…Phaahlamohlaka et al. found that a greater reducibility at low temperatures and higher Fischer‐Tropsch activity could be obtained when Co and Ru metals were in close proximity . The increased turnover frequency (TOF) based on Ru modified Co catalysts was attributed to the dissociation of CO into carbon and oxygen facilitated by bridge‐type CO adsorption .…”

“…[31] Phaahlamohlaka et al found that a greater reducibility at low temperatures and higher Fischer-Tropsch activity could be obtained when Co and Ru metals were in close proximity. [32] The increased turnover frequency (TOF) based on Ru modified Co catalysts was attributed to the dissociation of CO into carbon and oxygen facilitated by bridge-type CO adsorption. [33] Despite extensive experimental efforts on illustrating the effect of Ru promoter on the catalytic processes, the complementary atomic-level information on the dynamic structure and morphology change of Co nanoparticles induced by Ru has not been available.…”

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

“…[14] In FTS, hydrogen spillover has been only invoked to explain the role of noble metals (Pt, Ru, Au) as promoters for Co reduction in Co/Al 2 O 3 [15] or Co/C catalysts. [16] During FTS on Co/Al 2 O 3 catalysts, spillover results in more CH 4 and higher TOF due to the cleansing effect of atomic H. [15b] Many factors can promote hydrogen spillover on catalyst surface. 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 nanoparticles and support.…”

Beyond Cars: Fischer‐Tropsch Synthesis for Non‐Automotive Applications

“…As proven by many excellent works, the bifunctional catalyst is very attractive in many heterogeneous catalytic reactions, such as F‐T synthesis. The structure of these catalysts should be carefully designed as the bifunctional catalyst is sensitive to the intimacy and interaction between two components . Matching these tandem catalytic reactions with suitable component percentage, reaction conditions, spatial distance is also crucial to success.…”