Studies have been made of the catalytic oxidation of propylene to hexadiene over thallium oxides. The reaction is selective to the 1,5-diene, the only other product being carbon dioxide which originates from the overoxidation of the hexadiene. The active component has been found to be the thallic oxide, which is reduced during the course of the reaction. Permanent deactivation of the catalyst, which occurs if thallous salts distil out of the reactor, may be avoided if sufficient oxygen is present to rapidly reoxidize the catalyst. The production of hexadiene is favored at high temperatures, although the catalyst may deactivate faster under these conditions. A reaction mechanism is proposed in which the high selectivity to the 1,5-dimer is explained in terms of the simultaneous donation of two electrons to a Tl3+ion. © 1971.
Trimm, D. L., & Doerr, L. A. (1971). The catalytic oxidative dimerization of propylene. Journal of Catalysis, 23(1), 49–53. https://doi.org/10.1016/0021-9517(71)90023-6