Catalytic Performance and Sulfur Dioxide Resistance of One-Pot Synthesized Fe-MCM-22 in Selective Catalytic Reduction of Nitrogen Oxides with Ammonia (NH3-SCR)—The Effect of Iron Content

Abstract

The catalytic performance of Fe-catalysts in selective catalytic reduction of nitrogen oxides with ammonia (NH3-SCR) strongly depends on the nature of iron sites. Therefore, we aimed to prepare and investigate the catalytic potential of Fe-MCM-22 with various Si/Fe molar ratios in NH3-SCR. The samples were prepared by the one-pot synthesis method to provide high dispersion of iron and reduce the number of synthesis steps. We have found that the sample with the lowest concentration of Fe exhibited the highest catalytic activity of ca. 100% at 175 °C, due to the abundance of well-dispersed isolated iron species. The decrease of Si/Fe limited the formation of microporous structure and resulted in partial amorphization, formation of iron oxide clusters, and emission of N2O during the catalytic reaction. However, an optimal concentration of FexOy oligomers contributed to the decomposition of nitrous oxide within 250–400 °C. Moreover, the acidic character of the catalysts was not a key factor determining the high conversion of NO. Additionally, we conducted NH3-SCR catalytic tests over the samples after poisoning with sulfur dioxide (SO2). We observed that SO2 affected the catalytic performance mainly in the low-temperature region, due to the deposition of thermally unstable ammonium sulfates.

Insight into the Origin of Excellent SO2 Tolerance and de-NOx Performance of quasi-Mn-BTC in the Low-Temperature Catalytic Reduction of Nitrogen Oxide

“…The bands belonging to gas phase NH 3 species decreased with increasing time exposed to NO + O 2 gas flow and disappeared in 6 min, and surfaced OH – species (3670 cm –1 ) also decreased. At the same time, the peaks located at 1718 and 1577 cm –1 assigned to the NH 4 + species on Brønsted (B) acid sites decreased with increasing time, and the peaks at 1425 and 1209 cm –1 ascribed to the coordinate NH 3 related to Lewis (L) acid sites were shifted and replaced by the gradually enhanced infrared absorption peaks at 1488, 1409, and 1290 cm –1 . − The peaks of NO species (1159 cm –1 ) and bidentate nitrate (1095 cm –1 ) appeared, which are generated by the oxidation of adsorbed NH 3 . The changes in the infrared adsorption peak indicate that the adsorbed NH 3 is the active species, Mn-BTC-335 °C has a stronger adsorption and activation ability for NH 3 , and the Eley–Rideal (E-R) mechanism occurs during the SCR de-NO x reaction.…”

“…More details regarding the calculations are shown in the Supporting Information. In our calculation, a cluster (37 T atoms) was used, and the cluster was optimized as the initial configuration first. − The results indicate that the N–H bond of NH 3 * first breaks at the L acid site to produce the H atom and NH 2 , and then, the broken H atom transfers to the terminal oxygen of the cluster to form a hydroxyl group to complete the activation of NH 3 , which is the key reaction step that determines the overall NH 3 -SCR reaction. For the E-R route, the resultant NH 2 then reacts with gaseous NO to form NH 2 NO and then transforms to HNNOH, which is a crucial intermediate , with two barriers of 0.73 and 0.7912 eV.…”

Studies of NO Reduction with Ammonia Over Copper Species Deposited on MCM‐41 Nanospheres ‐ Experimental Evidence of Reaction Mechanism

“…Low-temperature activity in the NH 3 -SCR has been reported for various catalyst systems, including char-based materials [5,6,7] and zeolites modified with transition metals. [8,9,10] To transition metals catalytically active in the low-temperature reduction of nitrogen oxides belong, among others, copper [9,11,12] and manganese, [13,14,15] used as main catalytically active components or in combinations with other metals, e. g., Cu-Fe, [16] Cu-Ce, [17] Mn-Ce, [18] Mn-Co. [19] Catalytic performance of the NH 3 -SCR catalysts strongly depends on the form and aggregation of catalytically active transition metal species as well as properties of the used catalytic support, such as surface acidity [20] or porosity. [21] Recently, a very promising catalytic performance in the lowtemperature NH 3 -SCR process has been reported for copper modified mesoporous silicas obtained by template ion-exchange (TIE) method.…”

“…Thus, to avoid heating of the flue gases downstream of the ESP unit and therefore limit operation costs of such installation, effective NH 3 ‐SCR catalysts operating at temperature below 250 °C is necessary. Low‐temperature activity in the NH 3 ‐SCR has been reported for various catalyst systems, including char‐based materials [5,6,7] and zeolites modified with transition metals [8,9,10] . To transition metals catalytically active in the low‐temperature reduction of nitrogen oxides belong, among others, copper [9,11,12] and manganese, [13,14,15] used as main catalytically active components or in combinations with other metals, e. g., Cu‐Fe, [16] Cu‐Ce, [17] Mn‐Ce, [18] Mn‐Co [19] .…”

Hydrotalcite-Modified Clinoptilolite as the Catalyst for Selective Catalytic Reduction of NO with Ammonia (NH3-SCR)

“…Most research on zeolite-supported catalysts involved standard modification procedures, such as solid-state ion exchange [29], incipient wetness impregnation [30], mechanical mixing with metal oxides [31], and many others. Alternatively, the active phase can be introduced directly on the synthesis level, as described in the previous study of Szymaszek-Wawryca et al [32,33], which concerned layered zeolites of the MWW family. However, so-called one-pot synthesis is possible only in the case of synthetic zeolites, which are generally more expensive compared to their natural counterparts.…”