Success in Development of Exhaust Gas Catalyst with Thermal Agglomeration Resistance 10x Higher than Conventional Materi
(PhysOrg.com) -- This dramatic improvement in thermal agglomeration resistance opens the road to a large reduction in the amount of rare metals used in exhaust gas purification technologies.
A research team headed by Dr. Hideki Abe, Senior Researcher of the Advanced Electronic Materials Center and Dr. Katsuhiko Ariga, Principal Investigator of the International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (President: Sukekatsu Ushioda) developed an exhaust gas catalyst material with approximately 10 times greater thermal agglomeration resistance than conventional materials. This dramatic improvement in thermal agglomeration resistance opens the road to a large reduction in the amount of rare metals used in exhaust gas purification technologies.
Environmental and energy technologies, represented by automotive exhaust gas purification, are necessary and indispensible for human society in the 21st century for satisfying both abundant energy supplies and safe and healthy life. Metal catalysts,2 which are the most critical element materials in environmental and energy technologies, are confronted with the problem of thermal agglomeration, in which the catalyst loses its activity as a result of bonding/fusion of the catalyst due to heat and the accompanying reduction in the number of catalytic active sites. As catalytic active sites of metal catalysts, mainly platinum, palladium, rhodium,4 and other rare metals5 are used. To compensate for the reduction in catalytic activity caused by thermal agglomeration, the current technologies unavoidable require consumption of large amounts of rare metals, as there is no other method of introducing a large excess of active sites in the catalyst. Therefore, in this research, the NIMS team developed a metal catalyst with high resistance to thermal agglomeration by controlling the topology6 of the material at the nano-scale, which is completely different from the conventional approach.
The developed material, called “Metallic Cell” (Fig. 1), consists of metal spheres with a cavity approximately 1/100mm in diameter, which is surrounded by a thin cell wall containing pores (channels) 1/1000mm in diameter that enable transmission of substances and energy to and from the outer world. Because “Metallic Cell” has a special topology by which the catalytic active site in the cell is protected by the cell wall, it demonstrates excellent long-term catalytic properties, even under high temperature conditions in which ordinary catalyst materials would lose their activity due to thermal agglomeration (Fig. 2).
Metallic Cell is synthesized by precipitating a platinum film on the surface of commercially-available polystyrene powder by chemical reduction in an alcohol solution at normal temperature and pressure, followed by heating to 500°C to vaporize the polystyrene. Accompanying vaporization of the polystyrene, the hollow topology is formed and pores through which the polystyrene gas escapes are opened in the platinum film, resulting in natural formation of the unique morphology of Metallic Cell shown in Fig. 1. The method used to synthesize Metallic Cell is extremely simple and can be applied not only to platinum, as described here, but also to a number of other metals which display catalytic activity, beginning with rhodium, which shows high activity in NOx purification. The applications of Metallic Cell are not limited to exhaust gas purification technology. Taking advantage of its excellent heat resistance and high scalability, a large reduction in the amount of rare metals used in many environmental and energy technologies is also possible, beginning with fuel cell technology.
Provided by National Institute for Materials Science
