Isomerization of Butene over ZnO-SiO2

Isomerization of n-butenes was investigated over binary oxides ZnO-SiO2 having different mole ratios and the nature of active sites and the mechanism of the reaction were examined.On mixing of ZnO and SiO2, there appeared acidic sites and basic sites on the surface. The type of the acid sites was of Lewis acid which was determined by IR study of adsorbed pyridine.The isomerization was not retarded by acidic molecule of CO2 but by basic molecules such as pyridine and ammonia. The products formed over the deuterated catalyst contained a small amount of D atoms. The results of co-isomerization indicate that the reaction involves intramolecular hydrogen transfer and that the slow step is C-H bond cleavage. Therefore, it is concluded that the isomerization of butenes takes place on Lewis acid sites and is initiated by the abstraction of hydride ion which is the rate determining step.