In this communication we address the crystal-chemistry implications of an oxygen absorption-desorption process. Nowadays these processes are of high interest in several technological applications. The compound under study is the hexagonal perovskite 6H-BaFeO2.7 [1] and we have studied the properties in relation to the oxidation of CO to CO2. As a first step, we must be aware of the fact that experimentally, in what transmission electron microscopy concerns, an “in-situ” study of the reaction is impossible. Furthermore, the very same conditions than in the catalytic reaction are impossible to reproduce in an “ex-situ” TEM experiment. However, taken into account that the most important steps in the catalysis process is the ability of the oxygen absorption-desorption, we have tried to monitor the evolution of the crystal structure of this compound in two different manners.
Due to the high vacuum inside the column of the electron microscope, along with the help of a high temperature stage and the high energy of the incident beam of electrons, a quite reductive atmosphere should be present and it should push this compound into desorb oxygen in a somehow similar way as it should happen in the studied reaction. A second approach to gain information about the process, was the possible stabilization of the catalyst at the intermediate working temperatures where the catalysis occurs. Thus, we have tried to stabilize the intermediate compounds that might show up in function of oxygen loss, as obtained in the thermo-balance.
We here present and discuss these careful studies and surprisingly we will present some common results from these two different experiments which we interpret as being at the very heart of the catalysis process.
[1] K. Mori, T. Kamiyama, H. Kobayashi, T. Otomo, K. Nishiyama, K. Itoh, T. Fukunaga, S. Ikeda, J. Appl. Cryst., 2007, 40, s-501-s505