Abstract: The decarbonylation and the structural transformation of co_2(CO)_6(PBu_3)_2 supported on ZrO_2, Al_2O_3, TiO_2 and SiO_2 have been studied by IR spectroscopy, UV diffuse reflectance spectroscopy, X-ray photoelectron spectroscope and temperature-programmed decomposition technique. It is seen that when the complex is supported on various oxides, the frequency bands of the terminal carbonyls shift to low wave numbers respectively. The order of v(CO) is: complex/TiO_2=complex/SiO_2, complex/Al_2O_3, complex/ZrO_2. The position of the UV-DRS peaks for supported complexes, which are related to the nature of Co-Co bond and Co-CO (ligand) charge tranfer, are essentially the same as that for unsupported complex. It is found that when these supported complexes are heated in vacuum, intensity of the terminal carbonyl of those supported on ZrO_2 and Al_2O_3 diminishes somewhat with the increasing of temperature, and at the same time intensity of the bridged carbonyl increases. As the temperature is raised to 300′C and 200′C, the carbonyl bands disappear respectively. However, the C-H frequency bands persist in the IR spectra, showing that the phosphine ligands still exist on the surface. When CO is admitted to these decarbonylated samples, the frequency bands of adsorbed CO are observed. it is noticed that as the samples exposed to air, the bands disappear at once. The carbonyl bands of complexes supported on TiO_2 and SiO_2 disappear completely at 150′C and no bands of bridged carbonyl appear, on these decarbonylated samples CO can not be adsorbed.
The decarbonylation processes of these supported complexes in vacuum and air were investigated According the experimental results, the structrual transformation of surface complexes on various oxides are proposed respectively. In addition, the surface reaction of supported complexes in H_2 and He atmosphere during TPDE was also investigated.
*Project supported by the Science Fund of the Chinese Academy of Sciences.