Surface-doping of Cr 2O 3 particles by the 119Sn Mössbauer probe : Influence of the gaseous environment on the dopant distribution

Abstract

Chromium sesquioxide with 119Sn(II) dopant cations located just at the solid-gas interface (in the topmost cationic layer of the crystallites) has previously been synthesized by thermal treatment, under hydrogen flow, of Sn(IV) bulk-doped hydrated amorphous Cr(III) oxide. After exposure of the resulting Sn(II)/Cr 2O 3 material to various reactive gases, the probe environment was studied using Mössbauer spectroscopy. The present work reports synthesis of Sn(II)/Cr 2O 3 under argon atmosphere, instead of hydrogen, which could modify the probe behavior in reactivity experiments. In addition, it shows that migration of the dopant from the bulk towards the surface of the crystallites depends upon the ability of the synthesis atmosphere to act as an electron donor for the oxide matrix. After exposure of these Sn(II)/Cr 2O 3 samples to chlorine, the 119Sn probe environment is found to be the same as for Sn(II)/Cr 2O 3 prepared under hydrogen, which excludes HCl involvement in the surface rearrangement process evidenced by previous Mössbauer investigations.