Cluster Model Simulations of Metal-Doped Amorphous Silicates for Heterogeneous Catalysis
M Caricato, JOURNAL OF PHYSICAL CHEMISTRY C, 125, 27509-27519 (2021).
This Feature Article discusses how cluster models can be effectively used for quantum chemistry simulations of metal-doped amorphous silicates. These materials have been successfully used as heterogeneous catalysts for a variety of reactions, including olefin metathesis and polymerization, and alcohol dehydration. The amorphous surface provides a large surface area and distorted metal sites that are very reactive. However, the disordered microscopic nature of these silicates makes them hard to characterize, and progress toward better catalysts relies on a trial-and-error approach. Simulations can in principle provide insights on structure-property relations that may lead to a rational design approach, but again the disordered structure of the active sites makes the formulation of reliable models difficult. Using cluster models, it is possible to create multiple replicas of the same site with different distorted structures and silica environments, such that one can obtain a more realistic picture of the behavior of the material. Simulations based on the METal-doped Amorphous SIlicate Library (METASIL), which includes 70 cluster structures for single-site Zr-, Nb-, and W-doped silica, show very good agreement with a variety of experimental characterization techniques. These calculations validate the models and, more importantly, they allow to identify important structural descriptors of the active sites as well as a number of potential issues in the interpretation of experimental data. The Feature Article also discusses what challenges are still open in the simulation of amorphous materials and how these may be addressed in combination with new approaches such as machine learning algorithms.
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