According to the previous work , AcAc-Zr was synthesized by modifying ZrO2 with acetylacetone (AcAc). 5.65 g of Zr-butoxide was added to 200 mL of 2-propanol, and stirred for 30 min. 2.50 g of acetylacetone was added to the solution and stirred for three h (molar ratio AcAc/Zr = 2.0). The resulting solution was taken out from the glove bag, 5 mL of 1 molar nitric acid was added, and then stirred for more than 10 hours (molar ratio H + /Zr = 0.4). The solution was heated to 80 °C using a hot stirrer in a draft chamber to evaporate the solvent, and then, AcAc-Zr powder was obtained.