Reversible structural change of Rh particles supported on GeO₂ submonolayers–SiO₂ in reduction and oxidation by XAFS, XRD, TEM and FTIR

Abstract

The behaviors of Rh particles and GeO₂ submonolayers supported on SiO₂ during oxidation and reduction have been investigated, revealing a structural change in the outermost support surface of supported metal catalysts, by means of XAFS, XRD, TEM and FTIR. Partial reduction of the GeO₂ overlayers in Rh/GeO₂/SiO₂ occurred to form RhGe alloy particles by reduction with H₂ at 423–723 K, as proved by direct Rh–Ge bonding observed by EXAFS at both the Rh- and the Ge-K edges. The RhGe alloy particles were transformed to Rh oxides and GeO₂ submonolayers by calcination at 673 K; conversely, these oxide phases were converted back to RhGe alloy particles by reduction at 423–723 K. These transformations on SiO₂ took place reversibly during the oxidation–reduction treatments. This is a unique structural change at the Rh/GeO₂ overlayer interface in contrast to the behaviors of Rh and Ge on bulk GeO₂ which were irreversible owing to subsidence of Rh into the GeO₂ bulk.

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