Studies on kinetics and reactions mechanism of La2−xKxCu1−yVyO4 layered perovskites for the combined removal of diesel particulate and NOx
Layered-type perovskite catalysts (A2−xA′xB1−yB′yO4±δ, where A, A′=La, K and B, B′=Cu, V), prepared by the citrates method and characterized by BET, XRD, and catalytic activity analysis, proved to be effective in the simultaneous removal of soot and NOx, the two prevalent pollutants in diesel exhaust gases, but only at temperatures as high as 450–500 °C, seldom reached at the exhaust line location unless next to the engine exit (close-coupled system). Furthermore, stability at high temperature (800 °C) was only poor for the most promising of the studied catalysts (La1.8K0.2Cu0.9V0.1O4).
A detailed kinetic study was carried out on this last perovskite by FT-IR analysis as well as by temperature-programmed and isothermal oxidation tests, by assessing the effect of the prevalent affecting parameters. Some of the reaction intermediates were singled out and several different and rather complex reaction schemes were finally hypothesized, involving reaction intermediates either present on the catalyst surface or on that of the carbon particulate itself. The role of the various elements on the perovskite composition was also defined. The effect of vanadium in particular seemed to be dominant in assuring a peculiar activity towards NOx reduction.