Peking University, Beijing, April 26, 2010: How to further reduce the pollution produced by automobile exhaust has been an important research subject in physics, chemistry and other related fields during recent years. Academician Wang Enge from the PKU School of Physics and Bai Xuedong of the Chinese Academy of Sciences’ Institute of Physics co-discovered and verified a new phase change mechanism of cerium oxide electric field-driven. This discovery was an influential step toward the final solution of the problem of the pollution caused by automobile exhaust, which is becoming increasingly urgent nowadays. The Journal of the American Chemical Society recently published this achievement in articles where Wang Enge is featured as a corresponding author.
Due to the high oxygen activity of cerium oxide, which makes it capable of releasing and absorbing oxygen through oxygen vacancy, the industry widely used it as a main active carrier for three-way catalyst materials and precious metal catalysts, which are applied to deal with exhaust gas. However, there is a great problem in this application: in practice, the transition from tetravalent cerium to trivalent cerium needs a very high temperature (>600K); therefore, the large amount of exhaust emitted during the start and the early runnings of cars cannot be effectively dealt with. This was a key problem that has remained unsolved for a long time in related basic research and practice.
Wang Enge and the study group found that automotive exhaust catalysts usually work by the adjustment of temperature and partial pressure of oxygen, and thus a high temperature is required in the transitional process. After some micro-dynamic analyses of cerium oxide phase transition, the group suggested a new mechanism which induces phase change by external electric field. They designed and built a micro-circuit in the in situ transmission electron microscopy made by their own, and applied bias to cerium oxide thin films in room temperature. The reduction from ceria to cerium oxide could be observed from the in situ. When the electric field was removed, cerium oxide was oxidized and changed into ceria again. The result showed that the phase transition is reversible and can occur with the use of an electric field.
It is the first time that the scientific community has successfully lowered the barrier to the detachment of oxygen from the lattice in cerium oxide through the simple adjustment of electric field bias, so that oxygen vacancy is produced and made to move. This new achievement can greatly reduce the operating temperature of cerium oxide, and thus the automobile exhaust treatment can be carried out in room temperature. The international academic circle has paid much attention to the research for its important scientific value and its prospect of general application in the reduction of emission and environmental protection.
Translated by: Pan Huanming
Edited by: Jennifer Yan
Source: PKU News (Chinese)
