Molecular-scale bling as a green catalyst

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Propylene oxide is a commoditychemical often used as a precursor to commercially relevantpolyurethanes. Unfortunately, current methods of producing it on an industrial scale are generally not profitable orenvironmentally friendly. New research, reported in a paper in this week's edition of Science, describes how it's possible to use clustersof only three silver atoms to effectively catalyze theoxidation of propylene to propylene oxide.

The catalyst is composedof groups of three silver atoms (Ag₃) supported byan amorphous aluminafilm. Reactions were carried out by flowing adilute gas mixture of propylene and oxygen in helium over and throughthe alumina support. Analysis of the reaction effluent foundthat propylene oxide, acrolein, and carbon dioxide were the primaryproducts—the latter two are undesired byproducts. As the temperatureincreased, the selectivity (the ratio between the amounts of twoproducts produced in a reaction) for propylene oxide over acroleinincreased. However, above 60°C a combustionreaction began thatresulted in less acrolein and more propylene oxide, but also a lot morecarbon dioxide.

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