Abstract
A series of 0–25 wt% H 3[W 12PO 40] (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/ZrO 2 calcined at 673 K is H 0=−9.3, but dried samples (393 K) showed near superacid strength, i.e. H 0≤−13.75. The sites are mainly strong Lewis acids, but TPA supported on stabilized ZrO 2 (calcined at 773 K) shows both strong Brønsted 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 ZrO 2; the greater the TPA content the higher the resulting surface area. Skeletal rearrangement of 1-butene to isobutylene proceeds on 5–25 wt% TPA/ZrO 2 but not on pure ZrO 2, the greater the TPA content the higher the initial selectivity towards isobutene. In contrast, 20 wt% TPA supported on SiO 2 formed no isobutylene.
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