fulltext.study @t Gmail

Ab initio X-ray absorption modeling of Cu-SAPO-34: Characterization of Cu exchange sites under different conditions

Paper ID Volume ID Publish Year Pages File Format Full-Text
53269 46961 2016 13 PDF Available
Title
Ab initio X-ray absorption modeling of Cu-SAPO-34: Characterization of Cu exchange sites under different conditions
Abstract

•The 6MR is the most energetically favorable site for a bare Cu+ ion in Cu-SAPO-34.•The presence of adsorbates decreases the energetic preference of Cu ions in a 6MR.•The calculated XANES capture the trends of the edge shift with oxidation state.•For Cu in Cu-SSZ-13 and Cu-SAPO-34, the XANES is independent of zeolite type.

Copper-exchanged SAPO-34 (Cu-SAPO-34) provides excellent catalytic activity and hydrothermal stability in the selective catalytic reduction (SCR) of NOx by using NH3 as a reductant. We find that the 6-membered ring (6MR) site is the most energetically favorable for a Cu+ ion while the 8-membered ring (8MR) sites are less favorable by about 0.5 eV with respect to the 6MR site in Cu-SAPO-34. Upon adsorption of molecular species (H2O, O, OH, O2), the energy differences between Cu in the 8MR and 6MR sites 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 a Cu2+ ion bound to 2 OH species is more stable when the oxygen chemical potential is sufficiently high. By comparing 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 given oxidation state. By studying the Cu K-edge XANES of several favorable structures in Cu-SAPO-34 in the presence of adspecies, the simulated XANES results capture the real trend of the edge shift with oxidation state and gives new insights into the experimentally determined XANES of Cu-SAPO-34 obtained under standard SCR conditions.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (139 K)Download as PowerPoint slide

Keywords
Copper; Density functional theory; Zeolite; SAPO-34; XANES
First Page Preview
Ab initio X-ray absorption modeling of Cu-SAPO-34: Characterization of Cu exchange sites under different conditions
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us
Publisher
Database: Elsevier - ScienceDirect
Journal: Catalysis Today - Volume 267, 1 June 2016, Pages 28–40
Authors
, , ,
Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us