H-2 reduction Of Pt/MoO3 was accompanied by an increase in the surface area. H-2-reduced Pt/MoO3 exhibited the largest surface area of 250m(2)/g at reduction degrees of 60-70%. The surface area was enlarged only when Pt/MoO3 was reduced after heating in a stream of H-2. The catalytic activity of H2-reduced Pt/MoO3 for heptane isomerization was also dependent on the extent of reduction. The highest isomerization activity appeared at a reduction degree of about 70%. Heptane was selectively isomerized on H-2-reduced Pt/MoO3 with reduction degrees below 80%, and the high selectivity was preserved even at high conversion levels. The catalytic behaviors of H-2-reduced Pt/MoO3 were strongly affected by heating atmosphere. Reduction after heating in H-2 provided a much more active and selective catalyst for heptane isomerization than reduction after heating in N-2. We suggest from the results of XRD measurements that reduction Of Pt/MoO3 through the formation of a HxMoO3 phase can be an important step to enlarge the surface area and to generate the active sites for heptane isomerization. (C) 2003 Elsevier Science B.V. All rights reserved.