Activity and selectivity in catalytic reactions of buta-1,3-diene and but-1-ene on supported vanadium oxides

The activity and selectivity in the oxidation of buta-1,3-diene, and oxidation and isomerization of but-1-ene on unsupported and supported V₂O₅ catalysts have been investigated in terms of the catalyst structure. The rate of oxidation is mainly determined by the number of surface V=O species on the catalyst for both buta-1,3-diene and but-1-ene. The roughness of the V₂O₅ surface affected the activity for buta-1,3-diene, but not for but-1-ene oxidation. It was also found that TiO₂ support increases the activity of the surface V=O for but-1-ene oxidation. The selectivity to maleic anhydride was determined by the number of V₂O₅ layers on the support for both reactions. When the number of V₂O₅ layers was 1 or 2, the selectivity was low, while it increased markedly with an increase in the number of V₂O₅ layers to 5, and attained a constant value above 5 layers. Both V₂O₅ and support were active for the isomerization of but-1-ene to cis- and trans-but-2-ene. On V₂O₅, the cis/trans ratio was low, while it was as high as 3 for the Al₂O₃ support. The rate and selectivity of the isomerization on supported catalysts were explained in terms of the structure of V₂O₅ on the support. Difference in the structure-activity/selectivity correlation between oxidation and isomerization and that between but-1-ene oxidation and buta-1,3-diene oxidation were also discussed.