title: Benzene selectivity in competitive arene hydrogenation: effects of single-site catalyst···acidic oxide surface binding geometry.
abstract: Organozirconium complexes are chemisorbed on Brønsted acidic sulfated ZrO2 (ZrS), sulfated Al2O3 (AlS), and ZrO2-WO3 (ZrW). Under mild conditions (25 °C, 1 atm H2), the supported Cp*ZrMe3, Cp*ZrBz3, and Cp*ZrPh3 catalysts are very active for benzene hydrogenation with activities declining with decreasing acidity, ZrS ≫ AlS ≈ ZrW, arguing that more Brønsted acidic oxides (those having weaker corresponding conjugate bases) yield stronger surface organometallic electrophiles and for this reason have higher benzene hydrogenation activity. Benzene selective hydrogenation, a potential approach for carcinogenic benzene removal from gasoline, is probed using benzene/toluene mixtures, and selectivities for benzene hydrogenation vary with catalyst as ZrBz3(+)/ZrS(-), 83% > Cp*ZrMe2(+)/ZrS(-), 80% > Cp*ZrBz2(+)/ZrS(-), 67% > Cp*ZrPh2(+)/ZrS(-), 57%. For Cp*ZrBz2(+)/ZrS(-), which displays the highest benzene hydrogenation activity with moderate selectivity in benzene/toluene mixtures. Other benzene/arene mixtures are examined, and benzene selectivities vary with arene as mesitylene, 99%, > ethylbenzene, 86% > toluene, 67%. Structural and computational studies by solid-state NMR spectroscopy, XAS, and periodic DFT methods applied to supported Cp*ZrMe3 and Cp*ZrBz3 indicate that larger Zr···surface distances are present in more sterically encumbered Cp*ZrBz2(+)/AlS(-) vs Cp*ZrMe2(+)/AlS(-). The combined XAS, solid state NMR, and DFT data argue that the bulky catalyst benzyl groups expand the "cationic" metal center-anionic sulfated oxide surface distances, and this separation/weakened ion-pairing enables the activation/insertion of more sterically encumbered arenes and influences hydrogenation rates and selectivity patterns.
authors.affiliation: †Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
authors.forename: Weixing
authors.initials: W
authors.lastname: Gu
authors.affiliation: †Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
authors.forename: Madelyn Marie
authors.initials: MM
authors.lastname: Stalzer
authors.affiliation: ‡Exploratory Catalysis Research, UOP LLC, a Honeywell Company, 25 East Algonquin Road, Des Plaines, Illinois 60017, United States.
authors.forename: Christopher P
authors.initials: CP
authors.lastname: Nicholas
authors.affiliation: ‡Exploratory Catalysis Research, UOP LLC, a Honeywell Company, 25 East Algonquin Road, Des Plaines, Illinois 60017, United States.
authors.forename: Alak
authors.initials: A
authors.lastname: Bhattacharyya
authors.affiliation: §Dipartimento di Chimica, Universita' degli Studi di Roma "La Sapienza" and INSTM UdR Roma, p.le A. Moro 5, I-00185, Roma, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Motta
authors.affiliation: ∥Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439 United States.
authors.forename: James R
authors.initials: JR
authors.lastname: Gallagher
authors.affiliation: ∥Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439 United States.
authors.forename: Guanghui
authors.initials: G
authors.lastname: Zhang
authors.affiliation: ∥Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439 United States.
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Miller
authors.affiliation: ⊥U.S. DOE Ames Laboratory, Iowa State University, Ames, Iowa 50011-3020, United States.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kobayashi
authors.affiliation: ⊥U.S. DOE Ames Laboratory, Iowa State University, Ames, Iowa 50011-3020, United States.|#Department of Chemistry, Iowa State University, Ames, Iowa 50011-3020, United States.
authors.forename: Marek
authors.initials: M
authors.lastname: Pruski
authors.affiliation: †Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Delferro
authors.affiliation: †Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States.
authors.forename: Tobin J
authors.initials: TJ
authors.lastname: Marks