As part of a search for more thermostable supports for combustion
catalysts for gas turbine
applications, a series of complex oxide materials were prepared by
sol−gel synthesis and two
different coprecipitation routes. The materials were chosen on the
basis of literature studies;
two hexaaluminates (LaAl11O18 and
BaMnAl11O19
-
α), a
perovskite (SrZrO3), a spinel
(MgAl2O4),
and a pyrochlore (La2Zr2O7).
After synthesis, the materials were aged for 16 h in a flow
of
humid air at temperatures between 1100 and 1400 °C, simulating the
actual conditions in a
catalytic combustor. The aged samples were characterized by X-ray
diffraction, nitrogen
adsorption for determination of BET surface area, and scanning electron
microscopy. The sol−gel materials generally exhibited higher thermal stability than their
coprecipitated counterparts.
One exception was LaAl11O18, which had the
highest surface area of all materials, 8 m2/g,
after
aging at 1400 °C, both for the sol−gel synthesized and one
coprecipitated material. The reaction
paths for the high-temperature solid-state reactions depended on
preparation procedure and
stoichiometry of the product.