A Rh catalyst (Rh/Al/Mg 5/24/71 a.r.), able to ensure high stability under severe reaction conditions, was obtained via a hydrotalcite-type precursor. The structure of the materials and the Rh position were thoroughly studied at each step of the preparation, from the precipitation to the final catalyst. The formation of an oxide solid solution of Rh, Mg, and Al was found by X-ray and neutron diffraction using Rietveld analysis. The formation of Rh dissolved in a Mg and Al matrix is responsible for the highly dispersed and active Rh catalyst obtained after reduction. The stability of the Rh on the surface after 100 It of time on stream was shown by determining the dispersion of the Rh before and after reaction (using HRTEM) and demonstrating the unchanged particle size distribution. (C) 2003 Elsevier Science (USA). All rights reserved.