EFFECT OF THE ADDITION OF SN TO ZIRCONIA ON THE ACIDIC PROPERTIES OF THE SULFATED MIXED-OXIDE

Zirconium hydroxide, tin hydroxide and the mixed hydroxide of tin and zirconium (1:9) have been prepared, sulfated with a 0.1 M aqueous H2SO 4 solution and calcinated at 873 K. The chemical composition of these solids has been characterized by chemical analysis, differential therm al analysis (DTA), X-ray photoelectron spectroscopy (XPS) and energy d ispersive X-ray (EDX-) scanning transmission electron microscopy (STEM ), and their structural and textural properties have been studied by B ET surface area and XRD techniques. The nature of the acid sites (Bron sted or Lewis) was characterized by in situ IR study of pyridine adsor ption and desorption and their amount was found to depend on the sulfa te content. Catalytic properties have been studied for the isomerizati on reaction of n-butane to isobutane, in the 423 to 523 K range and fo r propan-2-ol conversion, in the 373 to 473 K range. Addition of Sn to ZrO2 (SnO2:ZrO2=1:9) led to a solid solution and enhanced slightly (c a. 30%) the weak acid features of ZrO2 and removed the basic propertie s of pure SnO2 which was shown to convert propan-2-ol to acetone. Upon sulfation of ZrO2, SnO2-ZrO2[1:9] and SnO2, the acidity of the oxides was sharply enhanced. SO42-/SnO2, which was inactive for the isomeriz ation reaction, was only 60% less active than SO42-/ZrO2 for propan-2- ol dehydration. This shows that sulfation of SnO2 generates acid sites of moderate strength. The presence of only 10% of SnO2 in ZrO2 decrea sed the reaction rates per SO42- by a factor of six for the initial n- butane isomerization reaction and by a factor of seven for the propan- 2-ol dehydration to propene and diisopropyl ether. It is suggested tha t the presence of Sn decreases the electron acceptor properties of Zr and thus its acidity strength. Since the rate per sulfated species of both reactions decreased in the same proportion, one may consider that on SO42-/ZrO2 and SO42-/SnO2-ZrO2 samples there is no site of moderat e strength able to dehydrate propan-2-ol without isomerising n-butane.