Multi–Scale Model for the Rational Design of Fischer–Tropsch Catalysts

For the conversion of syngas to hydrocarbons, Fischer and Tropsch proposed a surface carbide mechanism, which involves direct CO dissociation and subsequent hydrogenation of chemisorbed carbon (C) to form CH_x monomers that initiate and grow hydrocarbon chains [1-4]. Meanwhile, Storch and coworkers suggested that condensation of oxygen–containing intermediates (HCOH, hydroxycarbene) was responsible for C–C bond formation [5, 6]. Although most of these reaction schemes have been studied over the last decades, there are conflicting views concerning the actual reaction intermediates as well as the correct sequence of intermediate and termination steps. This situation reflects the experimental difficulties of investigating the reactions for the Fischer–Tropsch (FT) mechanism. Molecular modeling  has been proven to be a helpful tool to complement and guide experimental studies. In order to anticipate the initiation and termination steps associated with the conversion of syngas (CO+H₂) to liquid hydrocarbons through FT synthesis, simulations were carried out employing theoretical methods such as Density Functional Theory (DFT) and Kinetic Monte Carlo (KMC); using Co and Co–based structures as the prototype catalysts. Consequently, using molecular simulations in combination with experiments lowers the costs related to design as the simulations can be used to screen only the useful catalysts that can be subjected to experiment. Moreover, the elucidation of this process provides an improved understanding of the molecular mechanisms of hydrocarbon formation from syngas.

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