Ft-ir Studies of the Reactivity of Vanadia-titania Catalysts Toward Olefins .3. Normal-butenes and Isobutene

The interaction of vanadia-titania catalyst with 1-butene, cis-2-butene, trans-2-butene, and isobutene has been investigated by FT-IR spectroscopy in the temperature range 150-673 K. The three normal butenes give at room temperature 2-butoxide species that can undergo at higher temperatures oxidative dehydrogenation to methyl ethyl ketone and later oxidative C-C bond cleavage to acetate species. Methyl-allyl species are also formed and can be isolated by low-temperature experiments in the case of 1-butene. These speces follow a different oxidative path with formation of butadiene, furan, and finally maleic anhydride. Starting from near 200 K, isobutene oligomerizes giving its dimer 2,4,4-trimethylpent-1-ene and higher oligomers. At room temperature, hydration to t-butoxide species is also observed. Further heating causes oxidative decomposition to acetone, carboxylate species, and, from the oligomers, cyclic anhydrides. Only traces of allylic oxidation products of isobutene can be found. All these reactions occur in the absence of gas-phase oxygen.