Spectroscopic Characterization of Dealuminated H-Mordenites: The Role of Different Aluminum Species on the SCR of NO with Methane

Determining the storage, availability and reactivity of NH3within Cu-Chabazite-based Ammonia Selective Catalytic Reduction systems

“…A very broad band is found in the spectra of H-CHA and Cu-CHA zeolites, with a maximum at 3611 cm À1 , corresponding to Brønsted acidic OH groups. In contrast, two kinds of bridging hydroxyl groups can be observed in the spectra of the dehydrated H-SSZ-13, Cu-SSZ-13 (67) and Cu-SSZ-13(100) zeolites, with bands at 3605 and 3585 cm À1 . It is known that CHA-type zeolites present four symmetrically non-equivalent acid OH groups, with approximately the same stability and acid strength; [43][44][45][46][47] three sites are part of an 8-ring connecting two cages, whereas the fourth group is in contact only with one cage.…”

“…The catalysts Table 1 summarises the chemical composition of the zeolite materials used here as catalysts. The elemental analysis of Cu-SSZ-13 (67) and Cu-CHA zeolites reveal varying Cu 2+ -exchange levels, which can be related to the different Si/Al ratio and hence, to the different population of Brønsted acid sites in the H-form parent materials. Furthermore, the 27 Al MAS NMR data show the presence of different amounts of EFAl species, attributed to the different synthesis method and/or Al content of the parent materials.…”

“…The studied Cu-zeolites were labelled as follows: Cu-SSZ-13(x), with x being the degree of Cu 2+ exchange in %. Cu-SSZ-13 (67) and Cu-CHA were prepared via wet ion exchange (WIE) of the calcined parent zeolite, using an aqueous solution of copper sulphate. Typically, 50 ml of a 0.1 M solution of CuSO 4 (Merck, 99%) was mixed with 1 g of the zeolite and magnetically stirred for 2 h at 80 1C.…”

“…The resulting sample was calcined in air with the following temperature program: 2 1C min À1 to 120 1C, held for 30 min; and finally 1 1C min À1 to 550 1C, and 4 h at this temperature. Cu-SSZ-13(100) was prepared via three successive ion exchanges of the parent Cu-SSZ-13 (67), following the procedure reported above.…”

“…Additionally, the high-temperature (HT) desorption peak, in the temperature range of 250-450 1C, is considered to be due to strongly bound NH 3 , arising from protonated NH 3 formed over the Brønsted acid sites. 60 After Cu 2+ -exchange, the NH 3 -TPD profile of Cu-SSZ-13 (67) shows the presence of an extra desorption peak (IT peak) at 320 1C, attributed to NH 3 adsorbed over the Cu 2+ sites, demonstrating that Cu 2+ -exchange provides additional adsorption sites for NH 3 , and consequently a reduction in the total number of Brønsted acid sites. 61 Accordingly, a significant decrease in the intensity of the HT peak is observed, together with a shift in the peak maximum to higher temperatures, indicating, as expected, a higher acid strength of the remaining Brønsted sites.…”