Thermal stabilization of γ-alumina with modification of lanthanum through homogeneous precipitation

Abstract

We examined the thermal stabilization of a catalyst support by surface modification of γ-alumina using the homogeneous precipitation reaction of aqueous lanthanum species with hexamethylenetetramine. The phase transition of alumina, its surface area loss and the solid state compounds with lanthanum oxides at elevated temperatures were examined in the temperature range of 600–1400 °C. At 1200 °C, the surface area was as high as 88–92 m 2/g for 0.5–1.5 mol% La addition compared with 45 m 2/g for pure alumina. At 1300 °C, 1.5 mol% La-modified Al 2O 3 showed the 27 m 2/g, which was higher than 6 m 2/g for pure alumina. At temperatures higher than 800 °C, major crystalline lanthanum species was present as LaAlO 3, however, over 1300 °C crystalline LaAl 11O 18 appeared. In the wide temperature range of 800–1300 °C, the surface area of the alumina with the homogeneous precipitation of lanthanum nitrate was larger than the impregnated support. The effect of less aggregate state of La-modified alumina was assumed for the present process.