Unraveling the Role of Metal-Support Interactions on the Structure Sensitivity of Fischer-Tropsch Synthesis

Abstract

Structure sensitivity plays a pivotal role in heterogeneous catalysis and the Fischer-Tropsch reaction is one of the prime examples of such a structure-sensitive reaction. The activity and selectivity of this reaction depend on the size of the nanoparticle and this trend is observed for a whole range of support materials. To understand why metal-support interactions do not affect this trend, a ReaxFF force field is developed that effectively mimics the broad variety of support materials and captures the metal-support interaction strength into a single structural parameter. Particles of 1-9 nm embedded on support materials are sampled using simulated annealing molecular dynamics and the effect of the metal-support interaction on the active site distribution is studied. It is found that although the size-dependency profile of various active site topologies depends on the interaction strength of the nanoparticle with the support, step-edge sites with an FCC(110) motif remain insensitive to the type of support. Based on microkinetic simulations, it is established that these sites are predominantly responsible for the observed atom-based FTS activity rationalizing why Fischer-Tropsch synthesis is structure-sensitive but support-insensitive.