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

We examined the thermal stabilization of a catalyst support by surface modification of gamma-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 degreesC. At 1200 degreesC, 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 1300degreesC, 1.5 mol% La-modified Al2O3 showed the 27 m(2)/g, which was higher than 6 m(2)/g for pure alumina. At temperatures higher than 800degreesC, major crystalline lanthanum species was present as LaAlO3, however, over 1300degreesC crystalline LaAl11O18 appeared. In the wide temperature range of 800-1300degreesC, 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. (C) 2003 Elsevier B.V. All rights reserved.