The Effect of the Crystalline Phase of Zirconia for the Dehydration of Iso-propanol

Zirconium hydroxide was synthesized by varying the aging time of the zirconyl chloride octahydrate at 100 .deg. C in aqueous solution and the resulting hydroxides were calcined at 700 .deg. C for 6 h to obtain the crystalline ZrO₂. The materials used in this study were characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), N₂-sorption, transmission electron microscopy (TEM), NH₃ temperature-programmed desorption (NH₃-TPD), CO₂-TPD and iso-propanol TPD analyses to correlate with catalytic activity for the dehydration of iso-propanol. The pure tetragonal ZrO₂ phase was obtained after 24 h aging of zirconium hydroxide and successive calcination at 700 .deg. C. The increase of aging time showed the production of smaller particle size ZrO₂ resulting that the higher specific surface area and total pore volume. NH₃-TPD results revealed that the relative acidity of the catalysts increased along with the increase of aging time. On the other hand, the results of CO₂-TPD showed the reverse trend of NH₃-TPD results. The best catalytic activity for the dehydration of iso-propanol to propylene was shown over ZrO₂ catalyst aged for 168 h which had the highest S_BET (178 m² g^-1). The catalytic activity could be correlated with high surface area, relative acidity and easy desorption of iso-propanol