Solid-state reaction in the system of CrOx-Al2O3 and CrOx-LaOx-Al2O3 and their sintering at 500-1100 degreesC were examined by X-ray diffraction, electron spin resonance (ESR) and surface area measurement for the development of heat-stable catalytic ceramic in lean-burn exhaust treatment. CrOx-LaOx-Al2O3 catalyst, even heated at 1000 degreesC in air, showed the removal conversion of 100% for C3H6, 95% for CO and 7% for NO at 500 degreesC for high velocity automotive lean-burn exhaust with A/F=18 and S.V.=10(5)h(-1). La-modification of catalyst was effective to high surface area stabilization and the improvement of complete oxidation activity of CO and hydrocarbons. (C) 2003 Kluwer Academic Publishers.