Ethanol synthesis from carbon dioxide on Rh10SeTTiO2 catalyst characterized by x-ray absorption fine structure spectroscopy

摘要

The active site structures and electronic states were studied for the Rh10Se/TiO2 catalyst by means of edge spectra and EXAFS. The rate and selectivity of ethanol synthesis from CO2 on Rh10Se/TiO2 had strong dependence on the heating temperature in vacuum (T-evac) (1). Corresponding to the maximum of rate and selectivity when the T-evac was 623 K, the distance r(Se-Rh) reached a minimum (2.41 Angstrom) by Se K-and Rh K-edge EXAFS analyses. The contracted Rh10Se cluster was found to have an electronic state similar to that of Rh3Se8 or RhSe2 rather than of metallic Rh. A new reaction path control is proposed by regulating the distance between the interstitial Se atom and the metal framework Rh-10. A strong peak due to Is --> np transition was observed around the Se K absorption edge. The peak intensity did not exhibit significant change when the T-evac was varied for Rh10Se/TiO2. On the other hand, the area of peak observed around 23,230 eV in Rh K-edge spectra gradually decreased when the T-evac was elevated for Rh10Se/TiO2. Hence, the Se atom surrounded by Rh-10 framework was always kept in anionic state, while the electronic state of Rh atoms gradually changed by the interaction with TiO2 surface. The change for Rh atoms was also supported by the gradual increase of r(Rh-Rh) Obtained by EXAFS with the temperature increase. In the case of Rh sites with lower total coordination number around Rh (Rh10Se/SiO2, Rh10Se/Al2O3, and Rh10Se/MgO), the reaction CO2 --> CO(a)+O(a) occurred predominantly and formed CO(a) poisoned the catalysis. (C) 1998 Academic Press. References: 25