Effect of crystalline phases and acid sites on the dehydration of 1-octadecanol to 1-octadecene over TiO2–ZrO2 mixed oxides

Abstract

TiO2–ZrO2 mixed oxides with different amounts of TiO2 were prepared by co-precipitation method and used to synthesize 1-octadecene from 1-octadecanol. The results show that the doping of TiO2 leads to the formation of Lewis acid sites and Bronsted acid sites on the TiO2–ZrO2 mixed oxides. For catalysts with TiO2 doping < 3 wt.%, the catalysts are in an intermediate state from the monoclinic and tetragonal zirconia crystalline phases to the amorphous form, and no Ti–O–Zr bond is formed. For catalysts with TiO2 doping ≥ 3 wt.%, an amorphous structure and Ti–O–Zr bond are formed. The crystalline phase of metal oxides, amount and type of acid sites simultaneously affect the performance of the catalysts. The acid sites on TiO2–ZrO2 mixed oxides with monoclinic and tetragonal zirconia crystalline phases have much lower dehydration activity than those with an amorphous form. Lewis acid sites are responsible for both the dehydration of 1-octadecanol to form 1-octadecene and the double carbon bond migration of 1-octadecene to form 2-octadecene. Bronsted acid sites mainly catalyze the double carbon bond migration of 1-octadecene.