Surface-doping of Cr2O3 particles by the Sn-119 Mossbauer probe - Influence of the gaseous environment on the dopant distribution

Chromium sesquioxide with Sn-119(II) dopant cations located just at the sol id-gas interface (in the topmost cationic layer of the crystallites) has pr eviously been synthesized by thermal treatment, under hydrogen flow, of Sn( IV) bulk-doped hydrated amorphous Cr(III) oxide. After exposure of the resu lting Sn(II)/Cr2O3 material to various reactive gases, the probe environmen t was studied using Mossbauer spectroscopy. The present work reports synthe sis of Sn(II)/Cr2O3 under argon atmosphere, instead of hydrogen, which coul d modify the probe behavior in reactivity experiments. In addition, it show s that migration of the dopant from the bulk towards the surface of the cry stallites depends upon the ability of the synthesis atmosphere to act as an electron donor for the oxide matrix. After exposure of these Sn(II)/Cr2O3 samples to chlorine, the Sn-119 probe environment is found to be the same a s for Sn(II)/Cr2O3 prepared under hydrogen, which excludes HCl involvement in the surface rearrangement process evidenced by previous Mossbauer invest igations. (C) 2000 Elsevier Science Ltd. All rights reserved.