Rh supported catalysts were prepared by impregnating rhodium(I) and rhoclium(III) complexes with and without heteropolyacids for the hydroformylation of styrene derivatives. The effect of the pore size of MCM-41 was considered. The addition of water showed a promoting effect with Rh(III) based catalysts. The amount of water showed also a big effect on the catalytic activity of the Rh(III) supported catalyst. The change of the temperature affects the selectivity of the reaction time of the reaction. Different heteropolyacids such as H(3)PMo(12)O(40)center dot xH(2)O (HPA-Mo-12) and H(3)PW(12)O(40)center dot yH(2)O (HPA-W-12) Were used as co-catalysts that were impregnated along with rhodium complexes on the inorganic supports. The results showed a clear effect of the heteropolyacid H(3)PW(12)O(40)center dot yH(2)O (HPA-W-12) in increasing the catalytic activity of the rhodium supported catalyst. (c) 2005 Elsevier B.V. All rights reserved.