Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 110, Issue 2, Pages 413-418Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1220240110
Keywords
surface catalysis; DFT calculations; organometallic chemistry; solid acids
Categories
Funding
- US Department of Energy Office of Science, Office of Basic Energy Sciences [DE-FG02-86ER13511]
- NSF [CHE-1048773, CHE-0923236]
- US Department of Energy, Office of Basic Energy Sciences [DE-AC02-06CH11357]
- Chemical Sciences, Geosciences and Biosciences Division, US Department of Energy [DE-AC0-06CH11357]
- CINECA [HP10BD82EA 2011]
- U.S. Department of Energy (DOE) [DE-FG02-86ER13511] Funding Source: U.S. Department of Energy (DOE)
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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 C-13-cross-polarization magic angle spinning nuclear magnetic resonance (C-13-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 (eta(5)-C5H5)(2)ZrR2 (R = H, CH3) and [eta(5)-C-5(CH3)(5)]Zr(CH3)(3) adsorbed on Bronsted superacidic sulfated alumina (AlS). The latter complex is exceptionally active for benzene hydrogenation, with similar to 100% of the Zr sites catalytically significant as determined by kinetic poisoning experiments. The C-13-CPMAS-NMR, DFT, and XAS data indicate formation of organozirconium cations having a largely electrostatic [eta(5)-C-5(CH3)(5)]Zr(CH3)(2)(+)center dot center dot center dot AlS- interaction with greatly elongated Zr center dot center dot center dot O-AlS distances of similar to 2.35(2) angstrom. The catalytic benzene hydrogenation cycle is stepwise understandable by DFT, and proceeds via turnover-limiting H-2 delivery to surface [eta(5)-C-5(CH3)(5)]ZrH2(benzene)(+)center dot center dot center dot AlS- species, observable by solid-state NMR and XAS.
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