Jt. Richardson et Mv. Twigg, REDUCTION OF IMPREGNATED NIO ALPHA-AL2O3 ASSOCIATION OF AL3+ IONS WITH NIO/, Applied catalysis. A, General, 167(1), 1998, pp. 57-64
Contrary to common belief that alpha-Al2O3 is an inert support for the
impregnation of base metal species, evidence is presented for the inc
orporation of Al3+ ions into NiO impregnated on alpha-Al2O3, thereby c
ausing the observed increase in reduction temperature. In agreement wi
th this proposed model of support dissolution/incorporation into the i
mpregnated material, temperature programmed reduction measurements on
samples of NiO prepared by coprecipitation with small amounts of Al3and by multiple impregnation of alpha-Al2O3 gave similar results. As p
redicted, treating alpha-Al2O3, in the form of rings or powder, with H
NO3 extracted small amounts of Al3+ at 30 degrees C and larger amounts
at 90 degrees C. During the calcination step following impregnation w
ith Ni(NO3)(2) . 6H(2)O, NiO is formed as the Ni(NO3)(2) crystals deco
mpose and Al3+ ions are extracted from the surface. These Al3+ ions ar
e then retained either in or in the vicinity of evolving NiO crystalli
tes. Successive impregnation steps result in further Al3+ extraction f
rom the support and additional increases in reduction temperature. (C)
1998 Elsevier Science B.V.