Charge Redistribution at the Embedded Rh-Alumina Interface

An X-ray photoelectron spectroscopy (XPS) study was performed on model systems of Rh nanoparticles embedded into Al2O3. One of the main tasks was the investigation of the possibility to distinguish the Rh particles embedded into alumina matrix with respect to those on the surface of the support by means of their different electronic properties. A new component in the XPS spectra was found in the embedded sample after H-2 treatment at 750 degrees C for 2 h. On the basis of these results and of other data, obtained by means of X-ray diffraction, temperature programmed reduction, N-2 physisorption, and H-2 chemisorption experiments, we suggest that this particular feature is associated with the encapsulation process of the metal nanoparticles rather than to the particle size effect. The anomalous charge redistribution of the embedded metallic clusters detected in the XPS measurements may be therefore used as a spectroscopic fingerprint of the embedding of Rh nanoparticles in Al2O3.