Growth and properties of small Rh particles within an NaX matrix - Thermal analysis, electron microscopy, IR and photoelectron spectroscopy

Rhodium dispersions with different distinct average particle sizes, ranging from 1-2 to 6 nm, are prepared in zeolite NaX from Rh complexes ion exchanged with constant degrees of exchange and autoreduced by temperature-programmed decomposition. Thermal analysis and photoelectron spectroscopy demonstrate different elementary steps of Rh precipitation starting from either chlorine-free or chlorine-containing complexes. The stabilization of the Rh+ state for the chlorine-free sample is concluded from photoelectron spectra of Rh 3d(5/2) and confirmed by IR spectra using the probe carbon monoxide. Different average sizes of Rh particles are evaluated from electron micrographs with standard deviations of 10-20%. The shifts of the electron binding energies in core level Rh 3d(5/2) and valence-band spectra agree with theoretical predictions for intrinsic particle-size effects and indicate a low contribution of the relaxation effect.