title: Surface structural-chemical characterization of a single-site d0 heterogeneous arene hydrogenation catalyst having 100% active sites.
abstract: 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 (13)C-cross-polarization magic angle spinning nuclear magnetic resonance ((13)C-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 (η(5)-C(5)H(5))(2)ZrR(2) (R = H, CH(3)) and [η(5)-C(5)(CH(3))(5)]Zr(CH(3))(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 (13)C-CPMAS-NMR, DFT, and XAS data indicate formation of organozirconium cations having a largely electrostatic [η(5)-C(5)(CH(3))(5)]Zr(CH(3))(2)(+)· · · AlS(-) interaction with greatly elongated Zr · · · O(AlS) distances of ~2.35(2) Å. The catalytic benzene hydrogenation cycle is stepwise understandable by DFT, and proceeds via turnover-limiting H(2) delivery to surface [η(5)-C(5)(CH(3))(5)]ZrH(2)(benzene)(+)· · · AlS(-) species, observable by solid-state NMR and XAS.
authors.affiliation: Department of Chemistry, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Linda A
authors.initials: LA
authors.lastname: Williams
authors.forename: Neng
authors.initials: N
authors.lastname: Guo
authors.forename: Alessandro
authors.initials: A
authors.lastname: Motta
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Delferro
authors.forename: Ignazio L
authors.initials: IL
authors.lastname: Fragalà
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Miller
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks
mesh_terms: D000327:Adsorption; D000537:Aluminum Oxide; D001554:Benzene / Q000737:chemistry; D002247:Carbon Isotopes / Q000737:chemistry; D002384:Catalysis; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D006865:Hydrogenation; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods*; D009942:Organometallic Compounds / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties; D056928:X-Ray Absorption Spectroscopy / Q000379:methods*; D015040:Zirconium
chemical_list: D002247:Carbon Isotopes; D006841:Hydrocarbons, Aromatic; D009942:Organometallic Compounds; D015040:Zirconium; D001554:Benzene; D000537:Aluminum Oxide