Solid-state thermal behavior of copper-modified alumina toward lean-burn exhaust NO removal catalyst

Solid-state thermal behavior and catalytic activity of copper-modified alumina were studied in view of the possible use as automotive lean-burn NOx removal catalysts. The solid-state reaction of copper impregnated on an alumina support at elevated temperatures was examined by X-ray diffraction (XRD) and electron spin resonance (ESR), and the NO removal performance was evaluated under lean-burn conditions, The Cu-impregnated alumina subjected to heat-treatment at 900 degrees C in air showed a NO removal efficiency of 20% at A/F = 18 and space velocity = 100 000 h(-1). Novel Cu-modified Al2O3 was observed at the temperature range of 830-950 degrees C, which was characterized by XRD peaks appearing at d = 0.2-0.195, 0.241, and 0.268 nm, besides minute amounts of delta- and gamma-type Al2O3 were confirmed to be present. Structural stability of this modified alumina having de-NOx active Cu species was limited below temperatures of 930 degrees C. The authors propose the concept of bulk-state structural modification of alumina with Cu for the improvement of thermal durability of lean-burn de-NOx catalysts.