Low-temperature NO conversion with NH3 over cerium-doped MWW derivatives activated with copper species†

Abstract

Silica–alumina MCM-22 zeolite and its cerium-doped analogue (Ce-MCM-22) were obtained by one-pot synthesis. Additionally, the layered precursor of Ce-MCM-22 was subjected to delamination and pillaring procedures, resulting in the formation of Ce-ITQ-2 and Ce-MCM-36, respectively. The obtained micro- and micro-mesoporous supports were modified with copper cations by the ion-exchange method and tested as catalysts for NO conversion with ammonia. The zeolitic samples were characterized with respect to their chemical composition (ICP-OES), texture (low-temperature N₂-sorption), structure (XRD, FT-IR, UV-vis-DR), surface acidity (NH₃-TPD) and reducibility (H₂-TPR). Cu-functionalized zeolites were found to be active and selective catalysts for the selective catalytic reduction of nitrogen oxides with ammonia (NH₃-SCR) in the low-temperature range, effectively operating between 225 and 375 °C. The influence of bimodal porosity on the catalytic efficiency was observed when the space velocity of the reaction increased. The samples doped with cerium were more active than copper-modified silica–alumina MCM-22 in the process of NO-to-NO₂ oxidation, which is an important step in the fast-SCR process. The synergistic interaction of cerium–copper species together with a more open structure of the delaminated copper-modified sample (Cu–Ce-ITQ-2) influenced its activity in low-temperature NO conversion under humid reaction conditions.