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

Abstract

Hexaaluminate powder has been synthesized with the impregnation of La(NO 3) 3 and Mn(NO 3) 2 onto γ-Al 2O 3 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 LaAl 11O 19 and LaAlO 3 phases. The BET surface area of the manganese substituted powder and honeycomb decreased dramatically to ∼13 m 2 g −1 at 1200°C. Further heat treatments up to 1400°C did not cause a significant reduction of the surface area, ∼7 m 2 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.