Characterization of transition metal-impregnated LaAl complex oxides for catalytic combustion

Abstract

The effects of transition metals on LaAl complex oxide support were investigated in order to develop a high-temperature combustion catalyst. The properties of the catalysts were examined by X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), temperature-programmed reduction (TPR), and BET. The activities of the catalysts were investigated by methane combustion. Increasing the calcination temperature from 1000 to 1600°C resulted in the crystallization of each LaAl complex oxide from an amorphous form to the La-β-Al 2O 3 phase of a layered structure. During calcination, the addition of chromium retarded the crystallization of the support. However, the addition of copper to the LaAl complex oxide accelerated the crystallization of the support. The Cr-impregnated LaAl complex oxide retained a large surface area of 10 m 2/g even after calcination at 1400°C. However, the surface area of the Cu-impregnated LaAl complex oxide decreased abruptly to 1 m 2/g after calcination at 1400°C. The surface composition of chromium did not change significantly with increasing calcination temperature. However, the surface composition of copper decreased gradually with increasing calcination temperature, implying the formation of a solid solution with the LaAl complex oxide. Whereas the catalytic acitivity of the Cu-impregnated LaAl complex oxide decreased abruptly with increasing calcination temperature, most of the catalytic activity of Cr-impregnated LaAl complex oxide was maintained after calcination at 1400°C.