New Class of Catalyst Sports Shapely Selectivity

Mar 10, 2010
This breakthrough research was featured on the cover of Dalton Transactions. Journal cover published with permission from The Royal Society of Chemistry from Dalton Trans., 2010, 39, 1692-1694

A new class of catalytic material has been studied by scientists at Pacific Northwest National Laboratory. Metal-organic frameworks (MOFs) display a unique three-dimensional structure that is highly selective and reactive, with performance that is up to 50 percent better than commercial materials in the tested reactions.

The catalyst’s high shape selectivity—the ability to select certain molecules in the reaction based on structure—points to energy, environmental, and other applications for this new class of materials. This breakthrough research was featured as the cover of Dalton Transactions in February 2010.

Current commercial catalysts can convert to products up to 60 percent of reactants. Finding a stable catalyst, one that reliably converts 100 percent, means no waste and a faster, more efficient process. Stable and highly reactive catalysts that are also highly shape selective show potential for improving the refining of fossil fuels, utilizing biomass as , and reducing automobile exhaust pollutants, among other activities.

To be considered versatile, catalysts must have several attributes: high reactivity or conversion rate; large surface area; and durability—a tolerance for high temperatures. For this study, a new class of MOF catalysts was synthesized and tested for a class of catalytic reactions known as alkylations, useful for petroleum refining. Researchers were looking at the rate of the reaction, and how the unique properties of this class of catalyst might select for the most desirable products of the reaction.

MOFs are crystalline, well-ordered, three-dimensional structures. They have open metal sites with large pores. Fine-tuning the pores, so that only certain reactions take place, could further define the catalyst for particular applications. The MOFs were exposed to the chemicals they were to convert, a.k.a., the reactants. The MOFs exhibited high shape selectivity, acting like a sieve to pick and choose which molecules get to participate in the reaction. This shape selectivity can be used to advantage when choosing a catalyst for a particular reaction.

Metal-organic frameworks were synthesized using a single tetrahedral building block. Their catalytic properties towards alkylation of toluene and biphenyl showed high selectivity for the para oriented product using these porous materials.

In addition to high shape selectivity, the open framework structures of these materials enabled greater surface area contact—up to the size of a football field in a teaspoon. The increased surface area contributes to increased conversion, the rate at which the catalyst converts the chemicals in the reactant. This new material converts up to 100 percent for the alkylation reactions studied, meaning no waste and a faster, more efficient process.

MOFs provide efficient and productive reactions, maintaining these reactions under high temperatures. Their unique, crystalline shape and high conversion rate are attractive for catalytic processes in both petroleum refining and chemical production. In addition, an analysis of the material’s porosity points the way to many other new applications such as carbon dioxide separations which are important for mitigating greenhouse gas emissions.

Further exploration of the unique structure of these materials is warranted to examine the shape selectivity properties for the production of several chemicals. For this, scientists need to identify the ”active sites” for the catalytic reactions. Furthermore, fine-tuning the porosity of the MOFs may yield even more gains in surface area and conversion.

Explore further: Towards controlled dislocations

More information: Thallapally PK, CA Fernandez, RK Motkuri, SK Nune, J Liu, and CHF Peden. 2010. "Micro and mesoporous metal-organic frameworks for catalysis applications." Dalton Transactions, 39(7): 1692-1694. DOI:10.1039/b921118g

Related Stories

Biomass as a source of raw materials

May 12, 2009

For the protection of the environment, and because of the limited amount of fossil fuels available, renewable resources, such as specially cultivated plants, wood scraps, and other plant waste, are becoming the focus of considerable ...

Watching Catalytic Reactions from Within

Jan 29, 2009

(PhysOrg.com) -- Researchers from Utrecht University, in The Netherlands, have demonstrated a new way to get a real-time, microscopic view of the inner workings of catalytic reactions.

New Ways to Use Biomass

Sep 22, 2008

(PhysOrg.com) -- Alternatives to fossil fuels and natural gas as carbon sources and fuel are in demand. Biomass could play a more significant part in the future. Researchers in the USA and China have now developed ...

Recommended for you

Towards controlled dislocations

Oct 20, 2014

Crystallographic defects or irregularities (known as dislocations) are often found within crystalline materials. Two main types of dislocation exist: edge and screw type. However, dislocations found in real ...

Chemists tackle battery overcharge problem

Oct 17, 2014

Research from the University of Kentucky Department of Chemistry will help batteries resist overcharging, improving the safety of electronics from cell phones to airplanes.

Surface properties command attention

Oct 17, 2014

Whether working on preventing corrosion for undersea oil fields and nuclear power plants, or for producing electricity from fuel cells or oxygen from electrolyzers for travel to Mars, associate professor ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Squirrel
not rated yet Mar 11, 2010
If you click the DOI link of Thallapally's article you will find it is free access.