Influences of heat treatment and DeNOx performance of cordierite honeycombs washcoated with spinel catalysts

Spinel powders MAl₂O₄ (M = Ga and Zn) have been prepared by the co-precipitation of aqueous solutions containing corresponding metal, aluminum nitrate and ammonium carbonate. The NO reduction activities of composite spinel type powders in the Ga₂O₃–Al₂O₃–ZnO (GAZ) system were studied, in regard to their high-temperature application as an automotive lean-burn exhaust catalyst. A correlation between the NH₃-TPD results and the activity of GAZ reveals that a high population of surface acid sites is important to achieve high activity. The cordierite honeycombs with cell sizes 100, 200, 400 and 900 cpsi (cells per square inch) were washcoated with the GAZ slurries and their NO reduction activity was evaluated. The durability of GAZ/cordierites was studied in the presence of H₂O vapor, SO₂ and O₂.