TY - JOUR
T1 - Surface structural-chemical characterization of a single-site d0 heterogeneous arene hydrogenation catalyst having 100% active sites
AU - Williams, Linda A.
AU - Guo, Neng
AU - Motta, Alessandro
AU - Delferro, Massimiliano
AU - Fragalà, Ignazio L.
AU - Miller, Jeffrey T.
AU - Marks, Tobin J.
PY - 2013/1/8
Y1 - 2013/1/8
N2 - Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state 13C-cross-polarization magic angle spinning nuclear magnetic resonance (13C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η5-C5H5)2ZrR2 (R = H, CH3) and [η5-C5(CH3) 5]Zr(CH3)3 adsorbed on Brønsted superacidic sulfated alumina (AlS). The latter complex is exceptionally active for benzene hydrogenation, with ∼100% of the Zr sites catalytically significant as determined by kinetic poisoning experiments. The 13C-CPMAS-NMR, DFT, and XAS data indicate formation of organozirconium cations having a largely electrostatic [η5-C 5(CH3)5]Zr(CH3)2 +···AlS- interaction with greatly elongated Zr···OAlS distances of ∼2.35(2) Å. The catalytic benzene hydrogenation cycle is stepwise understandable by DFT, and proceeds via turnover-limiting H2 delivery to surface [η5-C5(CH3)5]ZrH 2(benzene)+···AlS- species, observable by solid-state NMR and XAS.
AB - Structural characterization of the catalytically significant sites on solid catalyst surfaces is frequently tenuous because their fraction, among all sites, typically is quite low. Here we report the combined application of solid-state 13C-cross-polarization magic angle spinning nuclear magnetic resonance (13C-CPMAS-NMR) spectroscopy, density functional theory (DFT), and Zr X-ray absorption spectroscopy (XAS) to characterize the adsorption products and surface chemistry of the precatalysts (η5-C5H5)2ZrR2 (R = H, CH3) and [η5-C5(CH3) 5]Zr(CH3)3 adsorbed on Brønsted superacidic sulfated alumina (AlS). The latter complex is exceptionally active for benzene hydrogenation, with ∼100% of the Zr sites catalytically significant as determined by kinetic poisoning experiments. The 13C-CPMAS-NMR, DFT, and XAS data indicate formation of organozirconium cations having a largely electrostatic [η5-C 5(CH3)5]Zr(CH3)2 +···AlS- interaction with greatly elongated Zr···OAlS distances of ∼2.35(2) Å. The catalytic benzene hydrogenation cycle is stepwise understandable by DFT, and proceeds via turnover-limiting H2 delivery to surface [η5-C5(CH3)5]ZrH 2(benzene)+···AlS- species, observable by solid-state NMR and XAS.
KW - DFT calculations
KW - Organometallic chemistry
KW - Solid acids
KW - Surface catalysis
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U2 - 10.1073/pnas.1220240110
DO - 10.1073/pnas.1220240110
M3 - Article
C2 - 23269836
AN - SCOPUS:84872190532
SN - 0027-8424
VL - 110
SP - 413
EP - 418
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 2
ER -