The heptane isomerization activity Of Pt/MoO3-SiO2 reduced by H-2 at 773 K for 6 h was investigated, in particular its relation to the physicochemical properties. H-2-reduced Pt/MoO3-SiO2 With a larger amount Of MoO3 had a higher isomerization activity. The same tendency was observed in the activity for 2-propanol dehydration. The isomerization activity was related to the number of acid sites, which was determined from NH3-TPD. XRD studies of H-2-reduced Pt/MoO3-SiO2 showed that the formation of MoOxHy was promoted as the MoO3 loading was increased. The conversion of MoO3 to H1.68MoO3 in the initial stage of reduction varied with the amount Of MoO3; only a part Of MoO3 was converted to H1.68MoO3 in Pt/MoO3-SiO2 with a small amount of MoO3, while the complete conversion to H1.68MoO3 was observed in Pt/MoO3. Based on these findings, we conclude that the isomerization activity of H-2-reduced Pt/MoO3-SiO2 can be governed by the formation of MoOxHy, which is yielded from the reduction Of MoO3 through H1.68MoO3. (C) 2009 Elsevier B.V. All rights reserved.