Abstract: A method for synthesizing a sol solution for forming porous alumina films having high heat resistance and high specific surface area and excellent adhesion to various substrate surfaces is provided. The method can include preparing an alkoxysilane and an aluminum solution separately, precipitating a silicon compound adsorbed on aluminum hydroxide in a solution of the alkoxysilane and the aluminum solution, and washing the precipitate filtered from the mixed solution with water to prepare a precipitate cake. A slurry solution is prepared by adding water to the precipitate cake, a pH adjusting treatment is performed on the slurry solution, and then an autoclave treatment is performed to prepare SiO2Al2O3 containing sol solution. A pH value of the slurry solution is controlled within a specific pH range in which the solution state of the SiO2Al2O3 containing sol solution after the autoclave treatment is a sol state.

Abstract: Porous alumina having excellent heat resistance and coking resistance is provided. The porous alumina can include silica and barium oxide added to aluminum oxide, wherein a ratio of SiO2 addition amount to a total mass of aluminum oxide and SiO2 addition amount is defined as SiO2 addition ratio (mass %), a ratio of BaO addition amount to a total mass of aluminum oxide and SiO2 addition amount is defined as BaO addition ratio (mass %), when the SiO2 addition ratio is within a range of 3 mass % or less and the BaO addition ratio is within a range of 14 mass % or less, the silica and the barium oxide are respectively added to the aluminum oxide so that a specific surface area of the porous alumina measured by a measuring method after heat treatment is equal to or larger than a reference specific surface area of reference porous alumina.