The aim of this work was to study the Co,Ba,K/Zr02 catalyst for the removal of the most important pollutants emitted by diesel engines: soot and NOx The Ba(x)/ZrO2 solids (with "x" varying between 0 and 16 wt.% Ba) and the Co,Ba,K/ZrO2 system were prepared by wet impregnation and then calcined at 500 degrees C in air for 2 h. These solids were treated with NO + O-2 and the stability of the formed nitrates was analyzed under both oxidizing and inert atmospheres measuring the amount of NOx adsorbed by the catalyst. Besides, the Co,Ba,K/ZrO2 solid was studied as a catalyst for soot combustion. The soot/catalyst ratio was varied (1: 1, 1: 10, 1: 15 and 1:20) and the NOx content in the feed was also varied between 0 and 4%. From these results, an exploratory study concerning the reaction order with respect to NO was addressed; the reaction order was estimated at ca. 0.5 and the activation energy of the reaction was estimated at about 20 kcal/mol. (c) 2007 Elsevier B.V All rights reserved.