What is Catalyst? What is Chemical Substance?
Presentations at 13th Researchers Crossing in Chicago
• The 13th Japanese Researchers Crossing in Chicago (“JRCC”) was held at the Consulate-General of Japan in Chicago’s Japan Information Center on April 15, featuring presentations by four up-and-coming science researchers.
• The JRCC was founded for Japanese researchers studying various fields of science in Chicago to encourage communication and share their research interests and results. While the group consists of researchers in highly specialized areas, the seminar series targets and is open to the general public.
The four presentations were:
• Observation of Catalytic Reaction Using Metal Organic
Framework (“MOF”) Single Crystals by Kenichi Otake, Postdoctoral Fellow,
Observation of Catalytic Reaction Using
MOF Single Crystals
• According to Otake, the keywords to his research are catalyst, MOF, and single crystal.
• Catalysts are being used in our everyday life in numerous ways, both industrial and biological. Examples include the automotive exhaust filter, photosynthesis by plants, brewing of alcoholic drinks and alcohol digestion by the human body.
• We can see what happens to a substance during the catalytic reaction process in the “energy profile diagram,” which shows that there is a big difference in the level of activation energy depending on the presence of a catalyst. Otake wants to explore the structure of reaction intermediates (“transient species” formed within the multi-step reaction mechanism), which determines the level of activation energy and the effectiveness of catalytic reaction.
• A catalytic process goes like this: you obtain the final reaction product by affixing a catalyst to a material called “catalyst support,” which works to stabilize a catalyst in the reaction process and separates the catalyst from reaction intermediates. The use of a catalyst support is known to help improve the activation rate, study of which is now a significant research topic for the industrial and commercial purposes.
• Primary materials used as catalyst support for heterogeneous catalysts are stable porous materials such as silica, zeolite and zinc. They allow a catalyst to permeate through pores for easy attachment to the support. The problem is that those materials don’t have a uniform structure, making it difficult to study through observation the mechanism of catalytic reactions.
• A solution to this problem is to use a new type of porous material that has a uniform structure, which is called the metal organic framework (“MOF”). Composed of metal ions and organic linkers, a MOF has a “jungle-gym” structure. It can be obtained through chemical manipulation, and its pore size and chemical properties can be controlled by substitution of components. Currently, approximately 60,000 MOF structures are registered with the Cambridge Crystal Database.
• According to Otake, MOFs are advantageous because of their uniform pores and high designability of the pore size and chemical properties, while it is chemically and physically stable compared to well-studied porous materials such as silica and zeolite. Because only one type of catalyst goes into uniform pores, a catalyst’s characteristics can be measured through observing MOFs. This also enables researchers to study the mechanism of activation energy enhancement.
• Also, single crystal can be obtained in the MOF structure. A single-crystal material has a long-range order of constituent, and has a regular three-dimensional structure that extends throughout the sample. For instance, salt has a regular three-dimensional structure of Na (sodium) and Cl (chlorine). When X-ray is applied, a single-crystal structure produces an x-ray diffraction. An electron density map can be obtained through analysis of the X-ray diffraction pattern, and it can lead to the creation of an atomic model of the material, as well as the revelation of the composition, structure and arrangement of its molecules.
• Through a direct observation of single crystal, Otake expects to obtain the correct and precise information of the structure and valance of catalytic active sites. He also hopes to directly observe immediate species in catalytic reaction, which would reveal the true mechanism of catalysis.
• Otake has successfully synthesized MOF single crystals, inside of which he introduced catalytic site and observed various single-site catalysts. His research prospect is a further evaluation of catalytic activities through direct observation of intermediate species, Otake adde
Kenichi Otake, Postdoctoral Fellow, Northwestern University
An image of the metal organic framework (MOF)
The image is borrowed from Otake's presentation.