EXAFS AND IR STUDY OF THE CO-ADSORPTION-INDUCED MORPHOLOGY CHANGE IN RU CATALYSTS

EXAFS (extended X-ray absorption fine structure) and IR studies were performed on Ru catalysts supported on γ-Al2O3, MgO, SiO2, and Ti02 to elucidate the mechanism of the CO adsorption-induced disruption of metal clusters. EXAFS results show that after reduction, Ru atoms exist on all supports as small metal clusters, but the particle sizes and metal-support interactions vary with the support. CO adsorption onto Ru/γ-Al2O3 and Ru/MgO led to the disruption of Ru-Ru bonds. By comparing with IR spectroscopic observations it is concluded that new species like O-Ru-CO and O-Ru-(CO)2 on γ-Al2O3 and On-Ru-CO and (On-Ru)2-CO(n = 3, 4) on MgO are formed after CO admission. On the other hand, no evidence of disruption of Ru clusters by CO adsorption was obtained in Ru/SiO2 and Ru/TiO2. The IR study showed, contrary to previously proposed models, that no H2 evolution takes place during the CO adsorption-induced disruption. A new reaction scheme that is consistent with our observations is presented. © 1990, American Chemical Society. All rights reserved.