Ferrierite and Its Delaminated and Silica-Intercalated Forms Modified with Copper as Effective Catalysts for NH3-SCR Process

Abstract

<jats:p>The main goal of the study was the development of effective catalysts for the low-temperature selective catalytic reduction of NO with ammonia (NH3-SCR), based on ferrierite (FER) and its delaminated (ITQ-6) and silica-intercalated (ITQ-36) forms modified with copper. The copper exchange zeolitic samples, with the intended framework Si/Al ratio of 30 and 50, were synthetized and characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low-temperature N2 adsorption), form and aggregation of deposited copper species (UV-vis-DRS), surface acidity (NH3-TPD) and reducibility (H2-TPR). The samples of the Cu-ITQ-6 and Cu-ITQ-36 series were found to be significantly more active NH3-SCR catalysts compared to Cu-FER. The activity of these catalysts in low-temperature NH3-SCR was assigned to the significant contribution of highly dispersed copper species (monomeric cations and small oligomeric species) catalytically active in the oxidation of NO to NO2, which is necessary for fast-SCR. The zeolitic catalysts, with the higher framework alumina content, were more effective in high-temperature NH3-SCR due to their limited catalytic activity in the side reaction of ammonia oxidation.</jats:p>

Ferrierite and Its Delaminated Forms Modified with Copper as Effective Catalysts for NH3-SCO Process

“…Thus, this band indicates the presence of monomeric copper cations possibly located in the ion-exchange sites of zeolite [19]. A small shoulder at about 325 nm indicates small oligomeric copper oxide species, while a shoulder at higher wavelengths is characteristic of small CuO aggregates [19]. This is consistent with the result of the XRD analysis, which shows the presence of the reflections characteristic of CuO in a diffractogram of the Cu/Al-FER sample (Figure 1c).…”

“…In the case of Cu/Al-FER the main absorption peak is located at about 215 nm and is related to the presence of monomeric copper ions interacting with the oxygen of the zeolite framework (O 2− →Cu 2+ ). Thus, this band indicates the presence of monomeric copper cations possibly located in the ion-exchange sites of zeolite [19]. A small shoulder at about 325 nm indicates small oligomeric copper oxide species, while a shoulder at higher wavelengths is characteristic of small CuO aggregates [19].…”

“…The structure of zeolite catalysts on different stages of their synthesis was analyzed by the XRD method. In diffractogram of Al-PREFER precursor, presented in Figure 1a, the (200) diffraction peak at 2Θ = 6.8 • , indicating the interlayer distance of 1.3 nm, was identified [19,20]. In the diffractogram of calcined Al-PREFER the (200) reflection at 2Θ = 9.6 • , characteristic of condensated zeolite layers in ferrierite, appeared.…”

“…Synthesis of ferrierite and ITQ-6 zeolites, containing aluminum or titanium in the zeolite framework, was done according to the procedures presented earlier [19,20]. The brief descriptions of the all syntheses steps are presented below.…”

“…In the first step, below 300 • C, the reduction of Cu 2+ to Cu + occurs. While in the second step, Cu + to Cu 0 is reduced at higher temperatures, typically above 400 • C [19,31]. Thus, the results of H 2 -TPR are important for an analysis of the form and aggregation of copper species present in catalysts.…”