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 γ-Al2O3 and subsequent calcination at 1400°C. 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 ∼13 m2 g−1 at 1200°C. Further heat treatments up to 1400°C did not cause a significant reduction of the surface area, ∼7 m2 g−1 for both sample. The bending strength of the monolithic honeycomb decreased significantly when the temperature jumped about 300°C 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°C, to start at 480°C, comparable to that of the corresponding powder.