A thin-skinned catalyst for chemical reactions

December 13, 2012

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 new method and earlier incarnations of yolk-shell catalysts was the creation of the empty chamber between the skin and catalyst, the researchers reported.

Tsung said the unprecedented level of control is a significant step in the use of unique nanoscale chemical structures in the effort to impart greater selectivity and control on heterogeneous catalysis, a proven process used to create chemicals in nearly all areas outside of pharmaceutical research, which employs homogeneous catalysis.

Scientists have been looking for ways to exert greater selectivity in heterogeneous catalysis in an effort to expand its application and extend "green chemistry" benefits of reduced byproducts and waste, Tsung said.

The key to the nanocrystal is the extremely precise structure of the metal-organic framework, Tsung said, which gives the skin an intricate network of pore-like passages through which select gases or liquids can pass before contacting the catalyst and triggering the desired reaction.

"We can make these pores very precisely, just like your skin or like the membrane surrounding a cell," Tsung said. "We can change their composition and chemical properties in order to accept or reject certain types of reactions. That is a level of control chemists in a variety of fields are eager to see nurtured and refined."
-end-


Boston College

Related Nanocrystal Articles from Brightsurf:

Success in controlling perovskite ions' composition paves the way for device applications
Hybrid organic-inorganic perovskites have received much attention as potential next generation solar cells and as materials for light-emitting devices.

Well-formed disorder for versatile light technologies
Researchers at ETH have managed to make an efficient material for broadband frequency doubling of light using microspheres made of disordered nanocrystals.

CU student helps bridge teams at Clemson
Three teams of researchers at Clemson University have joined forces to unravel some of the mysteries surrounding perovskite nanocrystals, which are semiconductors with numerous applications, including LEDs, lasers, solar cells and photodetectors.

'Growing' active sites on quantum dots for robust H2 photogeneration
Chinese researchers had achieved site- and spatial- selective integration of earth-abundant metal ions in semiconductor quantum dots (QDs) for efficient and robust photocatalytic H2 evolution from water.

A safe and powerful safeguard for your whole body against deadly radiation
IBS scientists have reported a highly effective and safe nanocrystal to combat dangers doses of radiation by growing manganese oxide (Mn3O4) nanocrystals on top of the Cerium oxide (CeO2) nanocrystals.

Solar cells, phone displays and lighting could be transformed by nanocrystal assembly method
Smart phones, tablets and laptop displays, camera lenses, biosensing devices, integrated chips and solar photovoltaic cells are among the applications that could stand to benefit from an innovative method of nanocrystal assembly pioneered by Australian scientists from the ARC Centre of Excellence in Exciton Science.

Researchers discover new way to split and sum photons with silicon
A team of researchers at The University of Texas at Austin and the University of California, Riverside have found a way to produce a long-hypothesized phenomenon -- the transfer of energy between silicon and organic, carbon-based molecules -- in a breakthrough that has implications for information storage in quantum computing, solar energy conversion and medical imaging.

Armored with plastic 'hair' and silica, new perovskite nanocrystals show more durability
Researchers at the Georgia Institute of Technology have demonstrated a novel approach aimed at addressing the perovskite's durability problem: encasing the perovskite inside a double-layer protection system made from plastic and silica.

Balancing elementary steps for boosting alkaline hydrogen evolution
Recently, Professors Jin-Song Hu and Li-Jun Wan from Institute of Chemistry, Chinese Academy of Sciences and their collaborators designed the nanocrystals with tunable Ni/NiO heterosurfaces to target Volmer and Heyrovsky/Tafel steps in the alkaline hydrogen evolution reaction (HER) and discovered that such bicomponent active sites on the surface should be balanced for promoting HER performance.

From foam to bone: Plant cellulose can pave the way for healthy bone implants
Researchers from the University of British Columbia and McMaster University have developed what could be the bone implant material of the future: an airy, foamlike substance from plant cellulose that can be injected into the body and provide scaffolding for the growth of new bone.

Read More: Nanocrystal News and Nanocrystal Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.