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, ra nging from 1-2 to 6 nm, are prepared in zeolite NaX from Rh complexes ion exchanged with constant degrees of exchange and autoreduced by tem perature-programmed decomposition. Thermal analysis and photoelectron spectroscopy demonstrate different elementary steps of Rh precipitatio n starting from either chlorine-free or chlorine-containing complexes. The stabilization of the Rh+ state for the chlorine-free sample is co ncluded from photoelectron spectra of Rh 3d(5/2) and confirmed by IR s pectra using the probe carbon monoxide. Different average sizes of Rh particles are evaluated from electron micrographs with standard deviat ions of 10-20%. The shifts of the electron binding energies in core le vel Rh 3d(5/2) and valence-band spectra agree with theoretical predict ions for intrinsic particle-size effects and indicate a low contributi on of the relaxation effect.