Preparation, characterization, and methane total oxidation of AAl 12O 19 and AMAl 11O 19 hexaaluminate catalysts prepared with urea combustion method

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A series of AAl 12O 19 (A = La, Sr, Ba, Ca, Ce), AMAl 11O 19 (A = La, Sr; M = Cu, Mn, Fe, Ni, Mg) and Sr 1− x La x MnAl 11O 19 ( x = 0.2–0.8) hexaaluminates were prepared successfully using urea combustion method. The influences of the molar ratio ( R) of urea to the total metal ions in hexaaluminates and the urea combustion temperature on the formation of the hexaaluminates were investigated. The structure of the hexaaluminates was characterized using X-ray powder diffraction (XRD) and temperature-programmed reduction (TPR). The catalytic activity for methane combustion was evaluated. The results indicated that the preparation conditions were: for LaAl 12O 19, the value of R was 3, the combustion time was in the range from 40 to 60 min, and the combustion temperature was not less than 500 °C; For LaFeAl 11O 19 and LaMnAl 11O 19, the value of R was 3–7, the combustion time was 40 min, and the combustion temperature was less than 500 and 400 °C, respectively; for AAl 12O 19 (A = Sr, Ba, Ca, Ce), LaMAl 11O 19 (M = Cu, Ni, Mg), SrMAl 11O 19 (M = Cu, Mn, Fe, Ni, Mg) and Sr 1− x La x MnAl 11O 19 ( x = 0.2–0.8), the value of R was 3, the combustion time was 40 min, and the combustion temperature was 500 °C. The prepared hexaaluminates had pure hexaaluminate phase structure and excellent catalytic activity in the methane combustion.