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

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.</p

Enumerating active sites on metal nanoparticles: Understanding the size dependence of cobalt particles for CO dissociation

Detailed understanding of structure sensitivity, a central theme in heterogeneous catalysis, is important to guide the synthesis of improved catalysts. Progress is hampered by our inability to accurately enumerate specific active sites on ubiquitous metal nanoparticle catalysts. We employ herein atomistic simulations based on a force field trained with quantumchemical data to sample the shape of cobalt particles as a function of their size. Algorithms rooted in pattern recognition are used to identify surface atom arrangements relevant to CO dissociation, the key step in the Fischer- Tropsch (FT) reaction. The number of step-edge sites that can catalyze C-O bond scission with a low barrier strongly increases for larger nanoparticles in the range of 1-6 nm. Combined with microkinetics of the FT reaction, we can reproduce experimental FT activity trends. The stabilization of step-edge sites correlates with increasing stability of terrace nanoislands on larger nanoparticles

Bramble: adaptive common neighbor analysis (CNA) for the recognition of surface topologies in nanoparticles

In heterogeneous catalysis, the active site is the specific region on the catalyst surface where the chemical reaction occurs. It plays a vital role in facilitating reactions by providing a unique arrangement of atoms and chemical properties to promote the conversion of reactants into products. Identifying these atomic motifs is crucial towards the atom-scale understanding of catalysis. Towards this aim, the common neighbor analysis (CNA) procedure acts as a powerful computational method used to analyze and classify atomic structures in materials. It involves examining the local environment of each atom to identify and quantify the types of atomic coordination and bonding, providing insights into the structural properties and behavior of materials at the atomic scale. Bramble is an efficient C++-based command-line tool to perform the CNA analysis. Uniquely, it is coupled to a pattern identification library for facile identification of the CNA fingerprints. Furthermore, for unknown fingerprint it offers the option to perform a similarity analysis based on the minimization of the Hilbert-Schmidt norm