Olefin metathesis compares favorably to traditional methods, such as steam cracking, for producing commodity chemicals ranging from plastic products to gasoline components.  Metathesis reactions promoted by heterogeneous catalysts can be designed to be energy-efficient and cost-effective because they are solvent-free, generate little waste, require low catalyst loads, and operate with high yield.  In particular, the tungsten trioxide heterogeneous catalyst has received considerable attention for metathesis reactions, since it can maintain its stable structure within industrial reaction temperature ranges and can be easily deposited using physical or chemical approaches.  We show how tungsten trioxide promotes the metathesis of ethene and 2-butene to form propene, by following the two-stage Herisson-Chauvin mechanism.  First, we show that 2-butene preferentially forms W-carbene active sites, relative to ethene, so we show how the catalyst surface structure affects its activity for metathesis.  Then, we show how the propagation steps proceed at the W-carbene active sites.  By using density functional theory calculations and microkinetic modeling, we can predict surface coverages and turnover frequencies that can be compared to experimental data.  Finally, we discuss how these technologies may be applied to biomass conversion and other green chemistry technologies.

Elucidating the role of catalytic active sites in olefin metathesis

247th National Meeting (2014)

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