Heteropolyacids impregnated with rhodium(I) or (III) complexes were prepared and used as supported catalysts in the hydroformylation of alkyl alkenes. Two general types of catalysts were prepared and tested: rhodium(I) or (III) in the presence and in the absence of the heteropolyacid H3PW12O40 25H(2)O (adopted as HPW12) supported on MCM-41 (30 A). I-Octene was chosen as a model substrate. Different types of supported catalysts were tested in the hydroformylation of 1-octene and other alkyl alkenes. The effects of the temperature and the type of solvent on the reaction were studied. The results showed that the supported catalysts containing the heteropolyacid H3PW12O40, 25H(2)O (HPW12) along with rhodium(I) or (III) gave higher catalytic activity. In addition, the recycling of the supported catalysts was studied and the results showed again the important effect of the presence of HPW12 on the recycling of the rhodium catalysts. (c) 2006 Elsevier B.V. All rights reserved.