A New Insight into Active Cu²⁺ Species Properties in One‐Pot Synthesized Cu‐SSZ‐13 Catalysts for NO_x Reduction by NH₃

Abstract

The Cu‐SSZ‐13 catalysts with different copper content are prepared by one‐pot method and changing the mole ratio of Cu‐tetraethylenepentamine/Al2O3. Cu‐SSZ‐13 catalyst with 3.25 wt.% Cu exhibits excellent catalytic activity (operation temperature window of 145–490 °C), adaptability to high GHSV (gas hourly space velocity) and hydrothermal stability in NH3‐SCR reaction. The results of XRD Rietveld refinement coupled with H2‐TPR and EPR show that three active Cu2+ species (Cu1, Cu2 and Cu3) locate in various sites in the CHA (chabazite) structure and play different action in NH3‐SCR reaction. Cu1 species situated close to an eight‐membered‐ring play a crucial role in the low temperature activity for its optimum reduction ability. While Cu3 species located in the center of the hexagonal prism are the most stable and its content basically remains unchanged after SO2 pretreatment, which contributes to the excellent SO2 resistance.

Rare‐earth Yttrium Exchanged Cu‐SSZ‐39 Zeolite with Superior Hydrothermal Stability and SO2‐Tolerance in NH3‐SCR of NOx

“…Even the very low level of SO 2 inevitably produced from ultra‐low sulfur fuel greatly limits the applicability of the Cu‐zeolite catalysts reported so far due to their high sensitivity towards this gas [7] . For instance, the NO x conversion dropped by nearly 70 % after continuous poisoning of Cu‐SSZ‐13 zeolite with a concentration of SO 2 as low as 10 ppm for 50 h [7b] . Yu et al .…”

Effect of Cu Concentration on the Selective Catalytic Reduction of NO with Ammonia for Aluminosilicate Zeolite SSZ-13 Catalysts

“…Moreover, the number of Cu 2+ on the surface follows the order Cu 0.100 -SSZ-13 > Cu 0.125 -SSZ-13 > Cu 0.075 -SSZ-13 > Cu 0.050 -SSZ-13 > Cu 0.025 -SSZ-13. Chen et al 28 reported that isolated Cu 2+ species may alleviate the NO reduction in the low-temperature region. It probably one of the reasons why the Cu 0.100 -SSZ-13 sample exhibits the best low-temperature activity.…”

Effect of Copper Precursors on the Activity and Hydrothermal Stability of CuII−SSZ−13 NH3−SCR Catalysts

“…However, the copper ions from the precursors with small anions ions like NO3 − are more accessible to enter the pore, which generates more isolated Cu Ⅱ , and exhibits excellent NH3−SCR activity. The acid sites of the molecular sieve catalyst are beneficial to adsorption and activation of NH3, which is one of the key steps for the reduction of NO by NH3 molecules [2,37]. The ammonia temperature-programmed desorption (NH3−TPD) spectra of the Cu Ⅱ −SSZ−13 catalysts are shown in Figure 4.…”

“…Many studies have shown that the chemisorption of NH3 plays a significant role in the NH3−SCR performance [2,30,40]. The acid sites of the molecular sieve catalyst are beneficial to adsorption and activation of NH 3 , which is one of the key steps for the reduction of NO by NH 3 molecules [2,37]. The ammonia temperature-programmed desorption (NH 3 −TPD) spectra of the Cu II −SSZ−13 catalysts are shown in Figure 4.…”

“…The Cu II /Cu sur ratios of all fresh sample are reduced after aging as shown in Table 5. The isolated Cu II species facilitate the reduction of NO x at low temperature, which trigger the decrease of catalytic activity of the aged samples [37]. The Cu and Al contents of the A−SO 4 sample increase significantly and can be due to the serious destruction of the framework.…”