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<p></p><p><a>A crucial consideration for supported heterogeneous
catalysts is the non-uniformity of the active sites, particularly for Supported
Organometallic Catalysts (SOMCs). Standard spectroscopic techniques, such as
X-ray absorption spectroscopy (XAS), reflect the nature of the most populated sites,
which are often intrinsically structurally distinct from the most catalytically
active sites. With computational models, often only a few representative
structures are used to depict catalytic active sites on a surface, even though there
are numerous observable factors of surface heterogeneity that contribute to the
kinetically favorable active species. A previously reported study on the
mechanism of a surface organovanadium(III) catalyst [(SiO)V<sup>III</sup>(Mes)(THF)]
for styrene hydrogenation yielded two possible mechanisms: heterolytic cleavage
and redox cycling. These two mechanistic scenarios are challenging to
differentiate experimentally based on the kinetic readouts of the catalyst are
identical. To showcase the importance of modeling surface heterogeneity and its
effect on catalytic activity, density functional theory (DFT) computational
models of a series of potential active sites of [(SiO)V<sup>III</sup>(Mes)(THF)]
for the reaction pathways are applied in combination with kinetic Monte Carlo
(kMC) simulations. Computed results were t then compared to the previously
reported experimental kinetic study</a><a>.: 1) DFT free energy reaction pathways
indicated the likely active site and pathway for styrene hydrogenation; a heterolytic
cleavage pathway requiring a bare tripodal vanadium site. 2) From the kMC
simulations, a mixture of the different bond lengths from the support oxygen to
the metal center was required to qualitatively describe the experimentally
observed kinetic aspects of a supported organovanadium(III) catalyst for olefin
hydrogenation. </a>This work underscores
the importance of modeling surface heterogeneity in computational catalysis.</p><p></p></div></div>
Cooperative catalytically active sites for methanol activation by single metal ion-doped H-ZSM-5
