Low temperature surface diffusion and decomposition of [Rh(CO) 2Cl] 2 adsorbed on oxidized Al(100)

Abstract

The adsorption and decomposition of [Rh(CO) 2Cl] 2 on three different model Al 2O 3 supports were studied with high resolution electron energy loss spectroscopy (HREELS) and temperature programmed desorption (TPD). The aluminum oxide supports were prepared by oxidation of Al(100) single crystal with either oxygen or water at temperatures from 425 to 725 K to prepare Al 2O 3 films of three types: planar-dehydroxylated, porous-dehydroxylated, and planar-hydroxylated. TPD of adsorbed [Rh(CO) 2Cl] 2 showed that [Rh(CO) 2C1] 2 decomposed on the Al 2O surfaces above 275 K and that the decomposition kinetics were dependent on the substrate porosity. HREELS data showed that on the porous Al 2O 3 layers, [Rh(CO) 2C1] 2 diffuses to stable binding sites within the pore structure below 245 K after which decomposition proceeds. For [Rh(CO) 2C1] 2 on hydroxylated Al 2O 3 films changes in the OH stretch region of the HREELS spectrum indicate that [Rh(CO) 2C1] 2 reacts with surface OH groups below 275 K. The experiments demonstrate that HREELS can be applied to the study of adsorbates on oxide supports in spite of complications of strong oxide lattice modes and poor resolution due to the nature of the support.