Role of Active Phase in Fischer–Tropsch Synthesis: Experimental Evidence of CO Activation over Single-Phase Cobalt Catalysts

Abstract

In order to understand the role of Co catalysts with different phases on Fischer−Tropsch synthesis, single-phase face-centered-cubic (fcc) and hexagonal-close-packed (hcp) Co were synthesized via a two-step approach, involving the formation of single-phase CoO materials followed by reduction in H 2 . The physicochemical properties of Co catalysts were thoroughly characterized by XRD, SEM, TEM, TPR, and H 2 chemisorption. It was found that hcp-Co exhibits higher activity on hydrocarbon formation than fcc-Co in Fischer−Tropsch synthesis. For both catalysts, CO dissociation was suggested as the rate-determining step, on which hcp-Co presents ca. 40 kJ mol −1 lower activation energy than fcc-Co, in agreement with a reported computational study. As a result, hcp-Co is concluded to be the preferable phase for rational catalyst design.

Morphology Evolution of Hcp Cobalt Nanoparticles Induced by Ru Promoter

“…The optimized lattice constants for the bulk hcp Co are a = b = 2.507 Å and c = 4.069 Å, in good agreement with experimental measurement (a = b = 2.497 Å, c = 4.078 Å) [35] and theoretical values (a = b = 2.494 Å, c = 4.031 Å). [36] According to the space group symmetry, the stable exposed index facets of the hcp Co include the (0001), (10-10), (10-11), (10)(11)(12), (11)(12)(13)(14)(15)(16)(17)(18)(19)(20), and (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21) surfaces. Their starting geometries were obtained by cleaving the relaxed structure of bulk hcp Co along the appropriate normal directions.…”

“…Subsequently, hcp Co with much lower activation energy was evidenced experimentally by Lyu et al. as the preferred phase in comparison to fcc‐Co for CO dissociation in FTS . The higher activity of hcp Co nanoparticles is identified from various favorable active sites on exposed facets that not available for fcc Co nanoparticles.…”

“…[18] The higher activity of hcp Co nanoparticles is identified from various favorable active sites on exposed facets that not available for fcc Co nanoparticles. In addition, Ge et al have proposed that the corrugated Co (10)(11)(12) and Co (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24) surfaces can significantly enhance the reactivity toward CO dissociation by reducing the activation barrier compared to the flat Co(0001) and corrugated Co (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) surfaces. [19] The identification of the first CÀ C bond formation in chain growth by Su et al revealed that the preferential carbide mechanism on Co(10-11) is more selective to chain growth rather than methanation, while the preferential CO insertion mechanism on Co(0001) is opposite.…”

“…[19] The identification of the first CÀ C bond formation in chain growth by Su et al revealed that the preferential carbide mechanism on Co(10-11) is more selective to chain growth rather than methanation, while the preferential CO insertion mechanism on Co(0001) is opposite. [20] Recently, we have demonstrated the crystal-plane effect on catalytic activity that Co(10-11) surface possesses the higher activity for CO conversion and lower selectivity of CH 4 compared with the Co (0001) and Co (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) surfaces. [21] As a consequence, one could resort to the morphology control by exposing large active surface facets to enhance the catalytic activity of catalysts.…”

Novel Cobalt Catalysts Supported on Metal–Organic Frameworks MIL‐53(Al) for the Fischer–Tropsch Synthesis

“…Fischer–Tropsch synthesis (denoted as FTS) is a key procedure that can convert biomass, coal, and natural gas into hydrocarbon and other flexible production . It is well known that Co, Ru, and Fe metals are active as FTS catalysts . Among them, cobalt metal exhibited a higher activity for the CO hydrogenation process than the other active metals.…”