Nanosized Cu-SSZ-13 and Its Application in NH3-SCR

Abstract

Nanosized SSZ-13 was synthesized hydrothermally by applying N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as a structure-directing agent. In the next step, the quantity of TMAdaOH in the initial synthesis mixture of SSZ-13 was reduced by half. Furthermore, we varied the sodium hydroxide concentration. After ion-exchange with copper ions (Cu2+ and Cu+), the Cu-SSZ-13 catalysts were characterized to explore their framework composition (XRD, solid-state NMR, ICP-OES), texture (N2-sorption, SEM) and acid/redox properties (FT-IR, TPR-H2, DR UV-Vis, EPR). Finally, the materials were tested in the selective catalytic reduction of NOx with ammonia (NH3-SCR). The main difference between the Cu-SSZ-13 catalysts was the number of Cu2+ in the double six-membered ring (6MRs). Such copper species contribute to a high NH3-SCR activity. Nevertheless, all materials show comparable activity in NH3-SCR up to 350 °C. Above 350 °C, NO conversion decreased for Cu-SSZ-13(2–4) due to side reaction of NH3 oxidation.

Influence of Framework n(Si)/n(Al) Ratio on the Nature of Cu Species in Cu‐ZSM‐5 for NH3‐SCR‐DeNOx

“…According to the literature indications, the adsorption bands at about 200–260 nm can be assigned to oxygen‐to‐metal charge transfer related to Cu + or Cu 2+ cations stabilized by the zeolite framework [30,31] . The bands in the range of 260–550 nm proved the presence of the CuO species and [Cu‐O‐Cu] 2+ species [32,33] . The absorption in the range 550–900 nm is related to the d‐d transitions of Cu 2+ ions in pseudo‐octahedral coordination (e. g., Cu(H 2 O) 6 2+ ) [30,31] .…”

“…The low‐temperature peaks (<300 °C) are assigned to the reduction of isolated Cu 2+ to Cu + ions and to the reduction of CuO to Cu 0 . The peaks above 300 °C are associated with the reduction of highly stable Cu + ions to Cu 0 [33,34] . Besides isolated Cu 2+ and CuO species, the DR UV‐Vis analysis reveals the presence of [Cu‐O‐Cu] 2+ species.…”

“…[30,31] The bands in the range of 260-550 nm proved the presence of the CuO species and [Cu-O-Cu] 2 + species. [32,33] The absorption in the range 550-900 nm is related to the d-d transitions of Cu 2 + ions in pseudooctahedral coordination (e. g., Cu(H 2 O) 6 2 + ). [30,31] Clearly, for the materials with ZSM-5 synthesized at higher temperatures, the two maxima appear centered at ca.…”

“…The peaks above 300 °C are associated with the reduction of highly stable Cu + ions to Cu 0 . [33,34] Besides isolated Cu 2 + and CuO species, the DR UV-Vis analysis reveals the presence of [Cu-O-Cu] 2 + species. However, Wang et al [34] pointed out that it is not clear if the reduction of [Cu-O-Cu] 2 + species proceeds directly to Cu 0 or via Cu + .…”

An Application of Steady‐state Isotopic‐transient Kinetic Analysis (SSITKA) in DeNOx Process

“…The selective catalytic reduction of NO x with NH 3 under strongly oxidizing conditions (NH 3 −SCR) was first introduced in the early 1970s by Hitachi Zosen in Japan over V 2 O 5 ‐TiO 2 [51,52] . Currently, the investigated catalysts in NH 3 −SCR can be divided into three categories: noble metal‐based catalysts (e. g., Ag/Al 2 O 3 [53] ), transition metal oxides (e. g., Cu(Fe)‐Mg−Al, Mn/Ti‐Si [54,55] ) and transition metal ion‐exchanged zeolites (e. g., Cu(Fe)‐ZSM‐5, Cu‐SSZ‐13 [56–58] ). The studies can be found in numerous review articles [59–63] .…”