Kinetics study of the oxidative dehydrodimerisation and aromatisation of isobutene on Bi2O3–SnO2

The kinetics of the oxidative dehydrodimerisation and aromatisation of isobutene has been studied on a Bi2Sn2O7 system for a mechanistic understanding of the reaction. The rate of disappearance of isobutene has been found to be first order with respect to oxygen and second order with respect to isobutene. A good fit of the kinetic data with the Mars and van Krevelen model has been established. The kred and kox have been found to be 2.3×106 and 32×106 mol min−1 m−2 kPa−1, respectively, proving that the reduction of the catalyst is the rate-determining step. Studies were also done to verify the mechanistic pathway of the reaction. Previous workers have suggested that the reaction is essentially a consecutive reaction proceeding from isobutene to p-xylene through the intermediate dimer (2,5-dimethyl-1,5-hexadiene). Studies were done at increasing contact time to verify the mechanistic pathway of the reaction and the intermediate dimer was used as the reactant. Our results showed that the intermediate dimer is mainly oxidised to COx while p-xylene is formed through some direct parallel pathway from isobutene.