Effect of the CeO 2 content on the surface and structural properties of CeO 2–Al 2O 3 mixed oxides prepared by sol–gel method

Abstract

Mixed xCeO 2–Al 2O 3 oxides with different CeO 2 content ( x = 1–20 wt%) were prepared by sol–gel method. The effect of the CeO 2 content, atmosphere and temperature treatment during synthesis on the structure and properties of the xCeO 2–Al 2O 3 was investigated. xCeO 2–Al 2O 3 xerogels prepared from aluminum tri-sec-butoxide and Ce(III) nitrates have a pseudo boehmite-like structure. The Ce(III) ions stabilized under a reductive atmosphere randomly occupy vacant sites in tetrahedral and octahedral positions of Al 2O 3. The crystallization of γ-Al 2O 3 is suppressed and the textural properties of the mixed xCeO 2–Al 2O 3 oxides are stabilized at high temperature. Conversely, the treatment xCeO 2–Al 2O 3 xerogels in an oxidative atmosphere shows a progressive oxidation of Ce(III) to Ce(IV) with crystallization of γ-Al 2O 3 and formation of CeO 2 with fluorite-like structure as the temperature rises. The effect of CeO 2 on the catalytic performance xCeO 2–Al 2O 3-supported Pt catalysts in partial oxidation of methane reaction was tested. The Pt catalysts were obtained by two methods: (i) impregnation of the xCeO 2–Al 2O 3 supports with H 2PtCl 6·6H 2O and (ii) one-step preparation by addition of Pt precursor during the sol–gel synthesis. CeO 2-containing catalysts showed higher stability than Pt/Al 2O 3 catalyst obtained by impregnation method. The effect of the support was less evident when the catalysts were obtained by the one-step method. Pt catalysts based on sol–gel oxides preparation show higher thermal stability and result in higher Pt sintering resistance than conventional ones.