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Unraveling the nature and the identity of the active sites in heterogeneous catalysis via structure-dependent microkinetic modeling

  • Raffaele Cheula (Politecnico di Milano, Italy)
Date
Tuesday 31 March 2020
Time
Address
Hotel NH Noordwijk Conference Centre Leeuwenhorst

Raffaele Cheulaa, Matteo Maestria
aLaboratory of Catalysis and Catalytic Processes, Dipartimento di Energia, Politecnico di Milano, Via La Masa, 34, 20156, Milano, Italy

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 [1]. In this respect, multiscale analyses based on structure-dependent microkinetic modeling is acknowledged to be an essential key-tool to achieve a mechanistic understanding of the catalyst functionality. However, the effect of the structure of the catalyst on reactivity and selectivity is at present neglected in state-of-the-art microkinetic modeling. As such, a “material gap” hinders the analysis of the underlying mechanisms at the atomic-scale level. To fill this gap, the modeling of the catalyst structure under reaction conditions is required [2].

Here, we present the development of a methodology for the analysis of the structure-activity relation in heterogeneous catalysis. 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 [3]. 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 composition of the atoms at the surface is determined, and therefore the nature of the sites in reaction conditions is fully characterized. Then, microkinetic analyses are performed on the different sites in order to unravel the identity of the active site in reaction. Selected examples in the context of CH activation, water-gas shift and reverse water-gas shift on metal catalysts will be employed as showcases. As a whole, the proposed procedure provides an effective pathway to unraveling the nature and the identity of the active sites in reaction conditions. It represents a very important step to explicitly introduce the effect of catalyst structure in the microkinetic analysis of heterogeneous catalytic processes.

Acknowledgements

Support by European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (Project SHAPE – grant agreement No. 677423) is gratefully acknowledged. Computational support was provided by CINECA, Bologna (Italy) and Center for Research Computing at the University of Pittsburgh (PA).

References

  1. R. Schlögl, Angew. Chem., Int. Ed., 54, 3465–3520, 2015.
  2. M. Maestri, Chem. Commun., 53, 10244, 2017.
  3. R. Cheula, A. Soon and M. Maestri, Catal. Sci. Technol., 8, 3493-3503, 2018.
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