Thick-film coating of hexaaluminate catalyst on thermally stable ceramic substrates and the catalytic activity of the film for methane oxidation were investigated for high-temperature combustion applications. The hexaaluminate film coated on pure alumina substrate retained the initial composition after calcination at 1200°C and displayed slightly lower catalytic activity than bulk hexaaluminate catalyst calcined at the same temperature. At the calcination temperatures of 1400 and 1600°C, migration of the components of the film and substrate occurred and the catalytic activity decreased considerably. The hexaaluminate catalyst film heat-treated at 1600°C was almost inactive for methane oxidation, which is attributable to volatilization of Mn during the heat treatment. By direct coating of the hexaaluminate on aluminum titanate honeycomb followed by calcination at 1200°C, the film exfoliated and cracks appeared in the aluminum titanate honeycomb. With an alumina intermediate layer inserted between the film and honeycomb, the thermal stability of the hexaaluminate film on the substrate calcined at 1200°C was significantly improved and the catalytic activity of the film was comparable to that of bulk hexaaluminate catalyst.
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