Surface acidity and basicity of γ-Al 2O 3 doped with K + and La 3+ and calcined at elevated temperatures

Abstract

High temperature reactions in industry require catalysts with high stability. Basic metal oxides, K 2O and La 2O 3, were added to γ-Al 2O 3 in order to obtain supports with low acidity and high surface areas at high temperatures. Microcalorimetry and FT-IR were employed to determine the surface acidity and basicity using ammonia and carbon dioxide as the probe molecules. It was found that the addition of basic metal oxides inhibited the transformation of γ-Al 2O 3 to the forms such as θ-Al 2O 3 and α-Al 2O 3 when calcined at 1000 °C. Instead, X-ray diffraction (XRD) results indicated the formation of aluminates for the supported samples. The 6% K 2O/γ-Al 2O 3 sample retained high surface area of 188 m 2 g −1 and strong basicity (170 kJ mol −1 for CO 2 adsorption) when calcined at 600 °C. The sample retained the surface area of about 100 m 2 g −1 when calcined at 1000 °C. In this case, the sample possessed low acidity and basicity and may be used as a neutral support with high thermal stability. The addition of La 2O 3 onto γ-Al 2O 3 might cause even more loss of surface area when calcined at high temperatures. The formation of a perovskite phase LaAlO 3 on the surface of the La 2O 3/γ-Al 2O 3 samples calcined at 1000 °C led to the low acidity and basicity.