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Title: Benzene selectivity in competitive arene hydrogenation: Effects of single-site catalyst···acidic oxide surface binding geometry

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. Furthermore, the combined XAS, solid state NMR, and DFT data argue that the bulky catalyst benzyl groups expand the “cationic” metalmore » 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.« less
 [1] ;  [1] ;  [2] ;  [2] ;  [3] ;  [4] ;  [4] ;  [4] ;  [5] ;  [5] ;  [1] ;  [1]
  1. Northwestern Univ., Evanston, IL (Unuted States). Dept. of Chemistry.
  2. UOP LLC, Des Plaines, IL (United States)
  3. Sapienza University of Rome (Italy). Dipartimento di Chimica.
  4. Argonne National Lab., Argonne, IL (United States). Chemical Sciences and Engineering Div.
  5. Iowa State Univ., Ames, IA (United States). Ames Lab.
Publication Date:
Report Number(s):
Journal ID: ISSN 0002-7863
Grant/Contract Number:
AC02-06CH11357; FG02-86ER13511; AC02-07CH11358
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 137; Journal Issue: 21; Journal ID: ISSN 0002-7863
American Chemical Society (ACS)
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States); Ames Lab., Ames, IA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1214127; OSTI ID: 1234445