Abstract
On the basis of Extended Hückel Theory, empirical studies on the adsorption step involved in the selective oxidation of isobutene are presented, and compared with those obtained for the propene molecule. Investigations have been made of the interaction between linear clusters of some transition metal oxides (Cu +, Cu 2+, Fe 2+, Co 2+, Ni 2+, Zn 2+), a test oxide and an isobutene molecule. Significant differences in behaviour of both olefins exist; isobutene is more strongly adsorbed and more readily oxidized than propene, thus the selectivity towards aldehyde is less and the catalyst activities are greater. The results obtained agree qualitatively with the experimental data; calculated binding energies are greater for isobutene than propene, the greater stability of the intermediate explaining the greater adsorption and oxidation. The relative results between the model clusters are in agreement with the classification of the related oxides according to their activities and selectivities, and confirm the first step as a proton transfer. The calculated barrier heights involved in the transfer of a proton from the isobutene molecule to a cluster are of the same order of magnitude as the experimentally determined activation energies.
Published Version
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