Reduction of MoO<sub>3</sub> to Porous Molybdenum Oxides and Its Catalytic Properties for Alkane Isomerization

Abstract

The catalytic activity of partially reduced Pt/MoO3 for alkane isomerization was investigated. The surface area of Pt/MoO3 was markedly enlarged by H2 reduction to a maximum after reduction at 673 K for 12 h. Enlargement of the surface area was caused by formation of pores with diameters of 0.6-3 nm. The catalytic activity of partially reduced Pt/MoO3 for heptane isomerization increased with reduction temperature, and reached a maximum at 723 K. The catalytic activity for 2-propanol dehydration was very similar to that of heptane isomerization. The isomerization and dehydration activities of partially reduced Pt/Na-MoO3 rapidly decreased with increasing content of Na. In contrast, the hydrogenation of cyclohexene was promoted on catalysts containing Na. The isomerization and dehydration activities were related to the number of acid sites, determined by NH3-TPD. Therefore, the isomerization activity of partially reduced Pt/MoO3 depends on the activity as an acid catalyst. H2 reduction at 673 K enlarged the surface areas of H1.55MoO3 and Pt/MoO3, but not the surface area of MoO3. H1.55MoO3 and Pt/MoO3 reduced at 673 K had comparable activity for pentane isomerization, and were much more active than MoO3 reduced at 673 K, even after considering the differences in surface areas. Molybdenum oxyhydride, MoOxHy, was formed after the decomposition of hydrogen molybdenum bronze in the reduction of H1.55MoO3 and Pt/MoO3. On the other hand, MoO3 was reduced to MoO2 without the formation of hydrogen bronze. These results show that surface area and isomerization activity were improved by the formation of MoOxHy from HxMoO3.