Ab initio X-ray absorption modeling of Cu-SAPO-34: Characterization of Cu exchange sites under different conditions
- Washington State Univ., Pullman, WA (United States)
Copper-exchanged SAPO-34 (Cu-SAPO-34) provides excellent catalytic activity and hydrothermal sta-bility in the selective catalytic reduction (SCR) of NOxby using NH3as a reductant. Here, we find that the6-membered ring (6MR) site is the most energetically favorable for a Cu+ion while the 8-memberedring (8MR) sites are less favorable by about 0.5 eV with respect to the 6MR site in Cu-SAPO-34. Uponadsorption of molecular species (H2O, O, OH, O2), the energy differences between Cu in the 8MR and 6MRsites decreases and almost disappears. Further, a thermodynamic phase diagram study shows that a Cu+ion bound to a single H2O molecule is the most stable species at low oxygen potential values while aCu2+ion bound to 2 OH species is more stable when the oxygen chemical potential is sufficiently high. Bycomparing Cu K-edge XANES between Cu-SSZ-13 and Cu-SAPO-34 with Cu in different oxidation states,we conclude that it is difficult to differentiate the simulated XANES of Cu in these structures at a givenoxidation state. By studying the Cu K-edge XANES of several favorable structures in Cu-SAPO-34 in thepresence of adspecies, the simulated XANES results capture the real trend of the edge shift with oxidationstate and gives new insights into the experimentally determined XANES of Cu-SAPO-34 obtained understandard SCR conditions.
- Research Organization:
- Washington State Univ., Pullman, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER)
- Grant/Contract Number:
- CBET-1258717
- OSTI ID:
- 1418528
- Alternate ID(s):
- OSTI ID: 1358897
- Journal Information:
- Catalysis Today, Vol. 267, Issue C; ISSN 0920-5861
- Publisher:
- ElsevierCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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