The effect of the amounts of hydrogen in molybdenum bronze on the wrface area of its reduction product was studied. H-2 reduction of molybdenum bronze induced an increase in the surface area. Molybdenum bronze with the larger amount of hydrogen exhibited the higher surface area after H-2 reduction. The reduction process varied with the amount of hydrogen in molybdenum bronze. The formation Of MoO2 was suppressed and that of molybdenum oxyhydride, MoOxHy, was promoted by an increase in the amount of hydrogen. Molybdenum bronze decomposed to Mo4O11 and MoO2 on thermal treatment at 400 degrees C in a flow of N-2. The surface, area of the thermally treated bronze changed very little with H-2 reduction. We conclude from these results that the reduction of molybdenum, bronze to MoOxHy, of which the formation was dominated by the amount of hydrogen in molybdenum bronze, involved an enlargement in thl, surface area. (c) 2005 Elsevier B.V. All rights reserved.