Solid-state reaction between compositions and sintering behavior of powders at 600-1100 degreesC were examined by x-ray diffraction, electron spin resonance and surface area measurement. Manganese-alumina catalyst, which was even subjected to heat treatment at 1000 degreesC in air, had the NO removal conversion efficiency of 22% at 350-400 degreesC Structural change and chemical state of alumina-supported manganese catalytic powders were studied for the purpose of the improvement of performance in automotive lean-burn NOx removal treatment for a model lean exhaust with high space velocity of 100,000 h(-1). La-modification of support was effective to maintain high surface area of powder, however it did not lead to the improvement of NO removal activity for manganese-based catalyst.