CHESTNUT HILL, MA (Dec. 13, 2012) A chemical nanostructure developed by Boston College researchers behaves much like the pores of the skin, serving as a precise control for a typically stubborn method of catalysis that is the workhorse of industrial chemistry.
Scientists have been trying to develop so-called yolk-shell catalysts as a means of imparting greater selectivity on heterogeneous catalysis, a process used in most industrial chemistry, including the manufacture of fine chemicals, petrochemicals and agrochemicals.
Boston College Assistant Professor of Chemistry Chia-Kuang Tsung and his team developed a nanostructure that can regulate chemical reactions thanks to a thin, porous skin capable of precisely filtering molecules based on their size or chemical make-up, the group reported recently in the Journal of the American Chemical Society.
"The idea is to make a smarter catalyst," said Tsung. "To do that, we placed a layer of 'skin' on the surface that can discriminate between which chemical reacts or does not react with the catalyst."
The team started with a nanoscale metallic crystal, then applied a "sacrificial layer" of copper oxide over it, Tsung said. Next, a shell of highly refined material known as a metal-organic framework, or MOF, was applied to the structure. Immediately, the polycrystalline MOF adhered to the cooper oxide, forming and outer layer of porous "skin". At the same time, the MOF began to etch away the copper oxide layer from the surface of the crystal, creating a tiny chamber between the skin and the catalyst where the chemical reaction can take place.
Testing the structure with gases of varying molecular structure, Tsung said the skin proved it could allow ethylene, with the small molecule size, to pass through and reach the catalyst. The gas cyclooctene, with larger molecule size, was effectively blocked from reaching the catalyst. Tests showed the central difference between ne
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