Co,Ba,K/ZrO2 system as a NOx trap for the treatment of diesel exhaust pollutants

V.G.MILT; E.D. BANÚS; M.A. ULLA; E.E. MIRÓ

Rio de Janeiro

Congreso; ENPROMER 2005. 2nd Mercosur Congress on Chemical Engineering and 4th Mercosur Congress on Process Systems Engineering.; 2005

Considering that the main pollutants emitted from diesel exhaust engines consist of NOx and soot, the aim of this work was to study the NOx adsorption using the Co,Ba,K/ZrO2 system. Such a system was chosen because previous works with the Co,Ba,K/CeO2 system indicated the potential of its use for the simultaneous abatement of NOx and soot. Here, we wanted to incorporate ZrO2 to that system as a catalytic support, in order to take advantage of the NOx adsorption capacity of this support at low temperatures. Microbalance experiments were performed in a Cahn 2000 instrument in order to study the interaction of the solids with NO+O2. The following sequence of treatments was carried out: heating for 2 h at 400°C in He, cooling to 70°C, feeding a mixture of NO (4%) + O2 (18%) (He balance) at 70°C up to constant weight, heating up to 490°C (maintaining this temperature for 10 min), cooling down to 70°C, switching to He, and repeating the heating program with He flow. While the addition of barium to the ZrO2 support increases the  adsorption of NO+O2 both at 70°C and during the heating in the NO+O2 stream, the addition of K and/or Co to Ba/ZrO2 make the formed nitrate species unstable above 350°C, Co,Ba,K/ZrO2 presenting the higher NOx adsorption. During the heating under inert atmosphere, a weight loss was observed for all the catalysts, beginning at 400°C for Ba/ZrO2 and Ba,K/ZrO2, and at 250°C for the Co-containing samples. The solids were characterized before and after the full microbalance treatment by FTIR, XRD and LRS. While BaCO3, KNO3, K2CO3 and Co3O4 were the starting species at which Ba, K and Co were present in the studied systems, the presence of Ba(NO3)2, NO3- and the absence of K2CO3 were the main differences found by combining the employed characterization techniques.