Effect of calcination temperature on the properties of the mixed TiO₂-ZrO₂ oxides and their performance in the dehydration of octadecanol to octadecene

A series of mixed TiO₂-ZrO₂ oxide catalysts used for the dehydration of octadecanol to octadecene were prepared by doping TiO₂ in ZrO₂ and calcining at 350-500 ℃. With the increase of calcination temperature, the amount of Lewis acid sites on the catalyst surface gradually increases. The amount of Lewis acid sites on the catalyst calcined at 450 ℃ is the most, and when the calcination temperature is over 450 ℃, the amount of Lewis acid sites decreases. No Brønsted acid sites are found on the catalysts. The mixed TiO₂-ZrO₂ oxides calcined at temperature below 400 ℃ contain Ti-O-Zr bonds and amorphous structure. The mixed TiO₂-ZrO₂ oxides with calcination temperature above 400 ℃ show monoclinic and tetragonal phases of ZrO₂. The crystalline phase of the metal oxides and amount of the acid sites simultaneously affect the performance of the catalysts. The acid sites on the mixed TiO₂-ZrO₂ oxides with amorphous structure have much higher dehydration activity than those with monoclinic and tetragonal zirconia crystalline phases. The catalyst calcined at 400 ℃ has the highest yield of 1-octadecene.