Hydrothermal stability of CuSSZ13 for reducing NOx by NH3

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

“…In particular, as shown in Figure 15 for both Cu/SSZ-13 and Cu/SSZ-16, increasing Cu loading from intermediate to high levels invariably leads to decreased catalytic performance for aged catalysts. These initial results were later fully reproduced by Nam and coworkers, with their XRD measurements demonstrating severe structural damage for highly Cu-loaded catalysts following hydrothermal aging [41]. Two explanations seem possible: (1) somewhat non-intuitively, high Cu loadings induce a high degree of dealumination that destabilizes the SSZ-13 substrate; or (2) as suggested by Lobo and coworkers, copper aluminate and/or copper oxide species are formed during hydrothermal aging that perhaps catalyze the zeolite structure collapse [29].…”

“…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.…”

“…Hydrothermal stability depends on various parameters including catalyst composition, aging temperature and duration. Typically, aging at~700 • C and lower causes limited structural degradation of Cu/SSZ-13 (e.g., dealumination, surface area loss), while higher aging temperatures induce partial to even complete structural damage [37,41].…”

“…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.…”

Influence of the Sodium Impregnation Solvent on the Deactivation of Cu/FER-Exchanged Zeolites Dedicated to the SCR of NOx with NH3

“…The spectral region of N-H stretching vibrations was relatively complex, because the distortion of the NH 3 molecule upon coordination led to a splitting of the ν N-H,asym mode and to the activation of the ν N-H,sym mode. In fact, the symmetric N-H vibration (ν sym ) of NH 4 + is inactive toward IR vibration modes. Below 1800 cm −1 ( Figure 7B), resolved N-H bending modes of ammonia adsorbed on Brønsted and Lewis sites appeared.…”