(78d) Ex-Situ Prepared Cobalt-Manganese Nanoparticles As Model-Catalysts for Fischer-Tropsch Synthesis

Cobalt-based Fischer-Tropsch catalysts are industrially used catalysts for the production of Diesel-like syn-crude. This synthesis route enables use of renewable feedstocks, such as biomass towards the production of liquid propellants for mobile applications. Commercial Fischer-Tropsch catalysts are typically promoted by traces of Manganese, Zirconia or Platinum to enhance performance in terms of selectivity, activity and stability[1]. Yet, the mechanistic role of these promoters is in debate and requires clearly defined model-catalysts to elucidate effects of composition, size and shape. The classical synthesis route of these catalysts involves incipient wetness impregnation of a support material with an aqueous solution of reducible metal salts, e.g. Co(acetate) and MnNO₃. These precursors get subsequently reduced forming nano-sized crystallites that are catalytically active. Studying mechanistic effects on these catalysts turns out to be difficult, as the control over deposition of the promoter is not entirely controlled.

In order to achieve crystallites of equal size and composition, we synthesized these in a separate preparation step with subsequent immobilization, reduction and test in catalysis. The developed Poly-ol reduction protocol is able to produce stable 7-10nm sized crystallites in a uniform manner[2]. Subsequently in a second precipitation step, these catalysts can be “decorated” with promoters. Using this approach, the crystallites can be thoroughly analyzed by XRD and TEM before and after immobilization. In this work we present a method to produce uniform Cobalt crystallites and CoMn alloys for the use in mechanistic studies. With these catalysts the effect of size, shape and composition can be controlled leading to a more detailed understanding of promoters.

[1]        Khodakov et.al. Chem.Rev. 2007, 107 (5), 1692.

[2]        H. Bönnemann and W. Brijoux, Advanced Catalysts and Nanostructured Materials (1996), 165-196.