Skeletal isomerization of 1-butene on 12-tungstophosphoric acid supported on zirconia

A series of 0-25 wt% H-3[W12PO40] (TPA) impregnated on freshly precipitated Zr(OH)(4) were prepared. The solids were characterized by a Hammett indicator method, specific surface area and pore size measurements, pyridine adsorption FTIR and later tested as catalysts in the isomerization of 1-butene. Maximum acid strength of 5-20 wt% TPA/ZrO2 calcined at 673 K is H-0=-9.3, but dried samples (393 K) showed near superacid strength, i.e. H(0)less than or equal to-13.75. The sites are mainly strong Lewis acids, but TPA supported on stabilized ZrO2 (calcined at 773 K) shows both strong Bronsted and Lewis acidity. TPA addition to hydrated Zr(OH)4 stabilizes the surface area of the final calcined material in comparison with that of pure ZrO2; the greater the TPA content the higher the resulting surface area. Skeletal rearrangement of 1-butene to isobutylene proceeds on 5-25 wt% TPA/ZrO2 but not on pure ZrO2, the greater the TPA content the higher the initial selectivity towards isobutene. In contrast, 20 wt% TPA supported on SiO2 formed no isobutylene. (C) 1998 Elsevier Science B.V. All rights reserved.