Influence of the preparation procedure of NSR monolithic catalysts on the Pt-Ba dispersion and distribution Original Research Article

The preparation procedure of a structured NOx storage/reduction catalyst is investigated by optimizing washcoating of ceramic monoliths and subsequent incorporation of Pt and Ba as the active phases. Endurance and firm adherence of the alumina washcoat to the substrate has been achieved. Incorporation of platinum from Pt(NH3)4(NO3)2 has been studied by impregnation (filling the monolith channels) and adsorption from solution (ion exchange). Highly dispersed and well distributed platinum were obtained by the adsorption procedure at pH 11–12 and calcination temperature no higher than 450–500 °C. Barium was incorporated by dry or wet impregnation. The dry impregnation procedure led to a more homogeneous barium distribution on the surface of washcoat. The sample prepared by adsorption from solution and dry impregnation, for incorporation of Pt and Ba respectively, showed the best storage capacity, ca. around 2.1 μmol NOx per mg of BaO for a feedstream with 380 ppm NO and 6% O2 in nitrogen, and a space velocity of 32,100 h−1, and also complete release and reduction of the stored NOx when oxygen was shifted to 2.3% H2. Thus, a relation between good NOx storage behavior and Pt dispersion and Pt-Ba distribution, and the preparation procedure has been established.