Structural and ESR characterization of heat-stable manganese-alumina lean NO removal catalyst

Manganese (Mn) oxides supported by gamma aluminas were studied toward heat-stable automotive lean-burn NOx removal catalysts. The solid-state reaction and structural transformation at 600–1100°C were examined by X-ray diffraction and electron spin resonance (ESR). Mn-alumina catalysts subjected to heat treatment at 1000°C in air retained the NO removal conversion efficiency of 22% at 350–400°C for a model exhaust with S.V. = 100,000 h−1. The ESR suggested that a part of the dispersed Mn2+ changed to ESR-silent Mn3+ and formed clusters or disordered oxide of Mn at 1000°C.