There is no doubt that the rational interpretation of the structure-activity relation in catalysis is a crucial task in the quest of engineering the chemical transformation at the molecular level. In this respect, multiscale analyses based on structure-dependent microkinetic modeling are acknowledged to be an essential key tool to achieve a detailed mechanistic understanding of the catalyst functionality. In this talk, we propose a methodology to perform a structure-dependent microkinetic analysis of a catalytic process. The methodology makes it possible to unveil the nature and identity of the active site in a self-consistent manner. The methodology is based on the combination of microkinetic modeling and ab initio thermodynamics with Wulff constructions and Boltzmann statistics at given conditions of chemical potential in the reactor. First, ab initio thermodynamics is applied to characterize the bulk and surface structure of the catalyst. The three-dimensional shape of single-crystal nanoparticles and the corresponding distribution of active sites are calculated either with the Wulff construction method or Boltzmann statistics, especially at low nanoparticle sizes, where a statistical representation of the catalyst morphology is needed. In doing so, the structure and the coordination geometry of each atom at the surface are determined, and therefore the nature of the sites in reaction conditions is fully characterized. Then, microkinetic analyses are performed on the distribution of the sites in order to unravel the identity of the active site during the reaction. Selected examples in the context of water-gas-shift, reverse-water-gas shift, and CO<sub>2</sub> methanation on metal catalysts will be employed as showcases. As a whole, this methodology makes it possible a concomitant description of the nature of the catalyst material in reaction conditions and of its catalytic consequences in terms of reactivity. As such, it paves the way towards the use of first-principles methods for the interpretation of the experimental evidence in terms of structure-activity relationships.

Unveiling the nature and identity of the active site via structure-dependent microkinetic analysis

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