Trap efficiency of exhaust gas pollutants in microporous sorbents under representative driving conditions
Résumé
The objective of this study is to develop a Neutral Air Quality Impact Vehicle (NAQIV) using a system able to reduce the tailpipe emissions of a gasoline powertrain engine. A possible configuration is a bypass in the exhaust, close to the tailpipe, that stores pollutants during the cold start phase when most emissions occur. For this purpose, adsorption efficiencies of commercial sieved powders Activated Carbon (AC), and zeolites (BEA, MFI) were screened at trap temperatures of 25, 50, and 150 °C using two different exhaust gas compositions. These compositions are obtained from two different phases of the World Harmonized Light-Duty Test Cycle (WLTC): the first 100 s after the engine start, and the first “5 km” after a cold start, the latter being representative of typical emissions of an automotive vehicle on an average trip in urban areas. The aim is also to provide sorption capacity not only in respect to the conventional pollutants (CO, NOx, CO2), and the most common NMHCs present in the exhaust gas (toluene, i-pentane, n-pentane, acetylene, ethylene, and methane), but also towards unregulated pollutants such as NH3, CH4 and N2O (to be introduced in Euro 7 regulations). The experimental results reveal a superior performance of AC NMHCs adsorption (and particularly toluene, n-pentane and i-pentane) which is not affected by the presence of other pollutants, but is negatively impacted by rising temperature and flow gas composition. Among zeolites, only Cu/Beta and Cu/ZSM-5 display moderate adsorption capacity of NH3, NMHCs and NO. In particular, the adsorption of ethylene and acetylene over Cu/ZSM-5 is strongly promoted at lower H2O concentrations. Finally, desorption profiles of each pollutant were generated through Temperature Programmed Desorption (TPD) experiments, unraveling sorbate-sorbent interactions.