Transformations o f 1,5-hexadiene and 1,3,5-hexatriene on aluminum, gallium, and indium oxides

Conclusions

• 1. On the example of the transformations of 1,5-hexadiene at 450 and 520°, and of 1,3,5-hexatriene at 300 and 450°, on aluminum, gallium, and indium oxides it was shown that Al₂O₃ has a very weak, while Ga₂O₃ and In₂O₃ have a strong aromatizing (dehydrogenating) ability, but one that is less than that of Cr₂O₃. All three oxides catalyze migration of the double bond in dienic hydrocarbons. The main transformation products of 1,5-hexadiene are benzene and hexadienes, which are isomeric with the starting material, and benzene and cyclohexadienes in the case of 1,3,5-hexatriene. Hydrogenation products are also formed, as well as small amounts of hydrocarbons with a five-membered ring.

• 2. The obtained results can be explained by the fact that the formation of benzene from aliphatic C₆ hydrocarbons on Ga₂O₃ and In₂O₃ proceeds by the same scheme as on other oxide catalysts.

• 3. The change in the aromatizing (dehydrogenation) ability when going from Al₂O₃ to Ga₂O₃ and In₂O₃ correlates with their ability to be reduced and is opposite to the change in the heats of formation of these oxides.