Synthesis of manganese substituted hexaaluminate and its fabrication into monolithic honeycombs for catalytic combustion

Hexaaluminate powder has been synthesized with the impregnation of La(NO3)(3) and Mn(NO3)(2) onto gamma -Al2O3 and subsequent calcination at 1400 degreesC. The hexaaluminate powder was formed into monolithic honeycomb of 200 cpi. The results of X-ray diffraction of the samples showed that the powder and the monoliths consisted of LaAl11O19 and LaAlO3 phases. The BET surface area of the manganese substituted powder and honeycomb decreased dramatically to similar to 13 m(2) g(1) at 1200 degreesC. Further heat treatments up to 1400 degreesC did not cause a significant reduction of the surface area. similar to 7 m(2) g(-1) for both sample. The bending strength of the monolithic honeycomb decreased significantly when the temperature jumped about 300 degreesC as a thermal shock was applied. The manganese inserted as a catalyzing component in the magnetoplumbite structure allowed lean methane combustion, 1% over the honeycomb heated at 1400 degreesC. to start at 480 degreesC, comparable to that of the corresponding powder. (C) 2001 Elsevier Science B.V. All rights reserved.