Improving of cold-start and combustion emissions in lean NO conditions with active and selective AgAl mesoporous catalysts

Abstract

Mesoporous AgAl-MCM41 catalytic adsorbents were synthesized. Template-ion exchange (tie) and incipient wet impregnation (iwi) methods were employed to incorporate Ag. The presence of non-structural and structural Ag(I) ionic species were detected. As the former refers to the ions that occupy an active site, the latter are part of the support hexagonal network. In addition, Ag2O nanoparticles were observed.The samples were used in C7H8 adsorption at 100 °C and in the selective catalytic reduction of NOx with toluene as reductant and H2O. The maximum NOx conversion was achieved with AgAl-iwi catalyst. Under dry conditions, a conversion of 84% was reported. With 2 or 10% H2O, the conversion was maintained between 80 and 90% and it is maintained at 70% after 50 h of reaction and successive cycles of water incorporation. In addition, the amount of toluene adsorbed follows the next order: AgAl-iwi > AgAl-tie > Al-MCM41 > MCM41. Instead, the quantity of C7H8 desorbed by the AgAl-tie is 34% above 400 °C. The AgAl-iwi solid show a ratio between the adsorbed and desorbed toluene of 99% in a wide range of temperature. This behavior is due to the presence of non-structural Ag(I) ions, which are the adsorption sites for the toluene.Comparing the performance of these materials with the AgNa-mordenite, the AgAl-iwi is more active catalyst and effective adsorbent between 100 and 550 °C. Thus, the mesoporous structure allows a better dispersion of the active sites, as well as the diffusion of toluene.