I will discuss new computational methods for moding catalysis by atomically dispersed metals on amorphous supports.  Applications will feature the longstanding mystery of ethylene-induced initiation in the Phillips catalyst.  We analyze this process at molecular, pore, and catalyst/polymer pellet scales.  At the molecular scale, we present a viable initiation route via conversion of a <i>bis</i>(ethylene)Cr(II) complex to chromacyclopentane which then homolyzes one of its two Cr-C bonds.  The dangling radical remains attached to the metal through its other Cr-C bond while its radical end attacks a nearby Cr(II) site.  The result is two activated Cr(III) sites capable of Cossee-Arlman polymerization, and the overall pathway has a barrier of 133 kJ/mol, comparable to 120 kJ/mol estimates from experimental initiation times.  Poisson statistics suggest that, for typical Cr loadings, about 1% of Cr sites can be activated by this mechanism.  We further examine dangling bonds created by stress-induced fracturing due to polymerization in pores as a potential mechanism for activation of additional sites.  Finally, we present an analysis of Thiele modulus and effectiveness factors during the polymerization process to show that some of the observed time to develop full activity may be due to transport limitations. <br/>&lt;!--![endif]----&gt;<br/>

Modeling atomically dispersed catalysts on amorphous supports at multiple scales

254th National Meeting (2017)

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