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) methodswere employed to incorporate Ag. The presence of non-structural andstructural Ag(I) ionic species were detected. As the former refers to theions that occupy an active site, the latter are part of the supporthexagonal network. In addition, Ag2O nanoparticles were observed.The samples were used in C7H8 adsorption at 100 ºC and in the selectivecatalytic reduction of NOx with toluene as reductant and H2O. The maximumNOx conversion was achieved with AgAl-iwi catalyst. Under dry conditions,a conversion of 84 % was reported. With 2 or 10 % H2O, the conversion wasmaintained between 80 and 90 % and it is maintained at 70 % after 50 h ofreaction and successive cycles of water incorporation. In addition, theamount of toluene adsorbed follows the next order: AgAl-iwi > AgAl-tie >Al-MCM41 > MCM41. Instead, the quantity of C7H8 desorbed by the AgAl-tieis 34 % above 400 ºC. The AgAl-iwi solid show a ratio between theadsorbed and desorbed toluene of 99 % in a wide range of temperature.This behavior is due to the presence of non-structural Ag(I) ions, whichare the adsorption sites for the toluene.Comparing the performance of these materials with the AgNa-mordenite, theAgAl-iwi is more active catalyst and effective adsorbent between 100 and550 ºC. Thus, the mesoporous structure allows a better dispersion of theactive sites, as well as the diffusion of toluene.