Adsorption and oligomerization of isobutene on oxide catalyst surfaces. A Fourier-transform infrared study

Abstract

The F.t.i.r. spectra of isobutene adsorbed at 170–300 K on the pure oxides silica, alumina, magnesia and titania, as well as on the phosphated samples prepared by impregnation of these pure oxides and of silica–alumina with phosphoric acid have been recorded. At low temperatures (170–220 K), molecularly adsorbed species are observed on pure oxides, with a spectrum similar to that of liquid isobutene, although with specific perturbations of the modes primarily involving the vinylidene moiety. Isobutene is transformed only on titania even at low temperatures into a new compound identified as its dimer 2,4,4-trimethylpent-1-ene. On phosphated samples oligomerization occurs at 293 K, producing oligomeric species identified as 5–10 monomeric unit cationic polymers.