High‐Temperature Automotive Catalytic Nitrogen Oxide Reduction over Copper–Lanthanum–Alumina

Abstract

The synthesis and nitrogen oxide (NO) removal activities of composite powders in the copper‐lanthanum‐alumina(Cu‐La‐Al2O3)system were studied, in regard to their high‐temperature application as an automotive lean‐burn exhaust catalyst. The solid‐state reaction between the copper, the lanthanum, and the Al2O3support, at elevated temperature, was examined by X‐ray diffractometry and electron‐spin resonance. Lanthanum impregnation into the Al2O3support successfully helped to form active composite powders that could remove nitrogen oxides and consisted of gamma‐Al2O3and LaAlO3, after heat treatment at 900°C, and mainly CuLaAl11O19 at 1000°C. Cu2+cations were observed to be isolated in the present powders, even after heat treatment up to 1000°C. The evaluation of NO removal activity over lanthanum‐modified copper‐Al2O3 catalysts that were subjected to harsh heat treatment was performed using a model exhaust‐gas mixture of NO, carbon monoxide (CO), propene (C3H6), carbon dioxide (CO2), water vapor (H2O), and an excess of oxygen (O2). The catalyst that was composed of 20 mol% copper, 10 mol% lanthanum, and Al2O3 and heat treated at 900° and 1000°C in air showed NO removal conversion efficiencies of 14% and 8%, respectively, under the lean‐burn conditions of an air:fuel (A/F) ratio of 18 and a space velocity (SV) of 100000 h‐1. Lanthanum‐modified copper‐Al2O3 powders are potentially useful as a NO removal catalyst, when applied to an automotive lean‐burn exhaust.