Thermal durability of Cu-CHA NH3-SCR catalysts for diesel NO reduction

Environmentally-benign catalysts for the selective catalytic reduction of NOxfrom diesel engines: structure–activity relationship and reaction mechanism aspects

“…57% and 31%, respectively, suggesting an obvious dealumination process. Based on the commercial Cu-CHA catalyst from BASF Corporation, Schmieg et al 143 found that even after hydrothermal treatment at 800 1C for 16 h, which was comparable to 135 000 mile vehicle-ageing, this catalyst still exhibited more than 70% NO x conversion from 200 to 450 1C. The small pore structure in Cu-CHA catalysts was also expected to be more resistant to HC poisoning due to the difficulty in diffusion of HC with larger size, such as isobutane, with a kinetic diameter of 5.5 Å.…”

Recent Progress in Atomic-Level Understanding of Cu/SSZ-13 Selective Catalytic Reduction Catalysts

“…In contrast, hydrothermal degradation is typically irreversible due to permanent structural changes in the zeolite that result in, for example, loss of Brønsted acid sites and changes to the chemical or physical structure of Cu active centers. This explains why hydrothermal aging effects have been so extensively studied [39][40][41][52][53][54]. Prior studies have suggested that Cu/SSZ-13 durability enhancement can be achieved in a number of ways: (1) composition optimization, that is, choosing optimized Si/Al and Cu/Al ratios [31]; (2) zeolite particle size optimization [55]; (3) new synthesis methods development [30,[56][57][58][59]; and (4) introduction of stability enhancement additives.…”

“…In terms of Si/Al ratios, we note that this parameter has changed from~17.5 for the first generation commercial (BASF) catalyst [40], to~9.0 for the current state-of-the-art material [16,18]. This change is nontrivial; as suggested by Figure 2, a lower Si/Al ratio allows for a higher percentage of Cu 2+ -2Z sites at similar Cu loadings, thus reducing the formation of undesired CuOx clusters during hydrothermal aging.…”

“…Hydrothermal stability of Cu/SSZ-13 is a critical criterion for its practical applications; as such, hydrothermal aging effects have been extensively addressed [29,37,[39][40][41]. Hydrothermal stability depends on various parameters including catalyst composition, aging temperature and duration.…”

Selective catalytic reduction of NOx by NH3 for heavy-duty diesel vehicles

“…However, the toxicity of vanadium species together with the narrow operation temperature window has limited the practical application of vanadium-based catalysts. Accordingly, some transition metal exchanged zeolites, e.g., Fe-ZSM-5 [7][8][9], Cu-SSZ-13 [10][11][12][13], and Cu-SAPO-34 [14][15][16], and vanadium-free oxide catalysts, e.g., Ce-based [17][18][19][20][21][22][23][24], Fe-based [25][26][27], and Cu-based [28] oxides, have been studied as potential substitutes of vanadium-based catalysts for diesel vehicles. However, the quality of the diesel fuel in China is still relatively low, and the sulfur content in the diesel fuel is often rather high.…”