Reduced forms of Rh(III) containing MCM-41 silicas as hydrogenation catalysts for arene derivatives

Rhodium containing mesoporous siliceous materials with MCM-41 pore architecture have been prepared via a template directed hydrolysis-polycondensation of tetraethoxysilane and rhodium(III) chloride in aqueous ammonia. The effect of aging and hydrothermal conditions on rhodium incorporation and on the porous structure of the resulting solids has been examined using elemental analysis, powder X-ray diffraction (XRD), N-2 sorption measurements and transmission electron microscopy (TEM). Optimized synthetic conditions afforded MCM-41 materials with Si/Rh 1400 and 120. Subsequent reduction of rhodium oxides species by hydrogen emphasized that the growth of Rh-0 particles (2-3 nm) is controlled by the porosity of the support. The conditions and efficiency of this step were evaluated through H-2-TPR (temperature programmed reduction) and IR monitored CO adsorption studies. The resulting materials showed a good catalytic activity and stability in the hydrogenation of arene derivatives under mild pressure and temperature. Cis/trans selectivity of dimethylcyclohexanes was discussed in the light of dispersion measurements. (c) 2006 Elsevier B.V. All rights reserved.