The citronellal hydrogenation was studied on Ir/Nb 2 O 5 -SiO 2 catalysts.A series of catalysts was synthesized with different niobia contents (Ir/N1 1.10%; Ir/N2 2.54%; Ir/N3 3.25%; Ir/N4 5.30%wt%) using the wet impregnation method.These catalysts were reduced in hydrogen atmosphere at low or high temperatures, 473K (LTR) or 773K respectively.Their structural and surface properties were investigated by XRD, TEM, XPS, DTP, FTIR, H 2 chemisorption at 298 K and surface specific area by using the BET method.The X ray diffraction studies revealed only the peaks due to niobia, mainly in those with higher niobia loading.No diffraction lines due to Ir were observed due to its lower content and/or to its high dispersion.The catalytic tests in the hydrogenation of citronellal were carried out in a batch reactor operated at 6.2 bar of H 2 and 343 K.All catalysts showed higher selectivity to isopulegol and to their products due to the cyclization of the citronellal molecule.