Superbase character of alumina loaded with potassium by impregnation from ammoniacal solution

Abstract

Al₂O₃ has been loaded with potassium by impregnation from an ammoniacal solution and heated under vacuum at 573 K. The resulting catalyst [K(NH₃)/Al₂O₃] showed extremely high catalytic activity for the isomerization of alkenes. These catalysts had much greater activity than that of Al₂O₃ loaded with alkali metals by vapour deposition. The isomerization, over K(NH₃)/Al₂O₃, of pent-1-ene to pent-2-ene gave a 98% yield in 6 min at 201 K. The temperature-programmed desorption and IR spectra of Al₂O₃ after impregnation indicated that the metal amide-like species formed on the alumina is a catalytically active species.

Al₂O₃ loaded with KNH₂ was found to be more active than K(NH₃)/Al₂O₃ for the isomerization of 2,3-dimethylbut-1-ene. The basic strength of these catalysts was estimated to be at least H_–= 37.