担载的Co2(CO)6(PBu3)2络合物的表面化学

红外光谱表明当Co_2(CO)_6(PBu_3)_2羰基络合物担载于不同的氧化物上后, 其羰基振动频带位置的波数顺序为: 络合物/SiO_2=络合物/TiO_2>络合物/Al_2O_3>络合物/ZrO_2。当这四种担载络合物在真空中加热脱羰基时, 以ZrO_2和Al_2O_3为载体者出现相当于桥式配位羰基的振动频带, 分别至300 ℃和200 ℃时羰基完全脱去。以TiO_2和SiO_2为载体者,基本没有出现桥羰基的频带, 而且在较低的温度下羰基即可脱去。紫外漫反射光谱表明担载络合物与担载前相比其表征Co-Co键和Co—Co配位键性质的特征带仍然存在, 脱羰基后出现相当于Co~(+2)或Co_3O_4的特征谱带。程序升温分解反应发现在H_2气氛中有表面加氢反应发生。

SURFACE CHEMISTRY STUDY OF SUPPORTED CO2(CO)6 (PBu3)2 COMPLEXES

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.