TY - JOUR
T1 - Consequences of exchange-site heterogeneity and dynamics on the UV-visible spectrum of Cu-exchanged SSZ-13
AU - Li, Hui
AU - Paolucci, Christopher
AU - Khurana, Ishant
AU - Wilcox, Laura N.
AU - Göltl, Florian
AU - Albarracin-Caballero, Jonatan D.
AU - Shih, Arthur J.
AU - Ribeiro, Fabio H.
AU - Gounder, Rajamani
AU - Schneider, William F.
N1 - Funding Information:
The experimental research at Purdue on zeolite synthesis and characterization was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Award Number DE-SC0019026. The computational work at Notre Dame was supported by the National Science Foundation GOALI program under award number CBET-1258690. We thank the Center for Research Computing at Notre Dame, and EMSL, a DOE Office of Science User Facility sponsored by the Office of Biological and Environmental Research and located at Pacic Northwest National Laboratory, for support of computational resources. We thank John R. Di Iorio (Purdue) for assistance with zeolite synthesis and helpful technical discussions. Florian Göltl contributions were supported in part through NSF grant number CHE-1800284.
Publisher Copyright:
© The Royal Society of Chemistry.
PY - 2019
Y1 - 2019
N2 - The speciation and structure of Cu ions and complexes in chabazite (SSZ-13) zeolites, which are relevant catalysts for nitrogen oxide reduction and partial methane oxidation, depend on material composition and reaction environment. Ultraviolet-visible (UV-Vis) spectra of Cu-SSZ-13 zeolites synthesized to contain specific Cu site motifs, together with ab initio molecular dynamics and time-dependent density functional theory calculations, were used to test the ability to relate specific spectroscopic signatures to specific site motifs. Geometrically distinct arrangements of two framework Al atoms in six-membered rings are found to exchange Cu2+ ions that become spectroscopically indistinguishable after accounting for the finite-temperature fluctuations of the Cu coordination environment. Nominally homogeneous single Al exchange sites are found to exchange a heterogeneous mixture of [CuOH]+ monomers, O- and OH-bridged Cu dimers, and larger polynuclear complexes. The UV-Vis spectra of the latter are sensitive to framework Al proximity, to precise ligand environment, and to finite-temperature structural fluctuations, precluding the precise assignment of spectroscopic features to specific Cu structures. In all Cu-SSZ-13 samples, these dimers and larger complexes are reduced by CO to Cu+ sites at 523 K, leaving behind isolated [CuOH]+ sites with a characteristic spectroscopic identity. The various mononuclear and polynuclear Cu2+ species are distinguishable by their different responses to reducing environments, with implications for their relevance to catalytic redox reactions.
AB - The speciation and structure of Cu ions and complexes in chabazite (SSZ-13) zeolites, which are relevant catalysts for nitrogen oxide reduction and partial methane oxidation, depend on material composition and reaction environment. Ultraviolet-visible (UV-Vis) spectra of Cu-SSZ-13 zeolites synthesized to contain specific Cu site motifs, together with ab initio molecular dynamics and time-dependent density functional theory calculations, were used to test the ability to relate specific spectroscopic signatures to specific site motifs. Geometrically distinct arrangements of two framework Al atoms in six-membered rings are found to exchange Cu2+ ions that become spectroscopically indistinguishable after accounting for the finite-temperature fluctuations of the Cu coordination environment. Nominally homogeneous single Al exchange sites are found to exchange a heterogeneous mixture of [CuOH]+ monomers, O- and OH-bridged Cu dimers, and larger polynuclear complexes. The UV-Vis spectra of the latter are sensitive to framework Al proximity, to precise ligand environment, and to finite-temperature structural fluctuations, precluding the precise assignment of spectroscopic features to specific Cu structures. In all Cu-SSZ-13 samples, these dimers and larger complexes are reduced by CO to Cu+ sites at 523 K, leaving behind isolated [CuOH]+ sites with a characteristic spectroscopic identity. The various mononuclear and polynuclear Cu2+ species are distinguishable by their different responses to reducing environments, with implications for their relevance to catalytic redox reactions.
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U2 - 10.1039/c8sc05056b
DO - 10.1039/c8sc05056b
M3 - Article
AN - SCOPUS:85062073999
VL - 10
SP - 2373
EP - 2384
JO - Chemical Science
JF - Chemical Science
SN - 2041-6520
IS - 8
ER -