New Catalysts for Ester Hydrogenation and the Oxygen Reduction Reaction

• Author / Creator

  Xu, Shuai

• This dissertation reports a crosslinked catalyst organic framework, which was prepared by an alternating ring opening olefin metathesis polymerization (alt-ROMP) between dichloro{N,N'-bis({(2-diphenylphosphino)phenyl}methylidene)bicyclo[2.2.1]-hept-5-ene-2,3-diamine}-ruthenium, 1,2-N-di(cis-5-norbornene-2,3-endo-dicarboximido)-ethane, and cis-cyclooctene (COE) catalyzed by RuCl2(=CHPh)(PCy3)2 in the presence of a BaSO4 support. The heterogenized catalyst hydrogenated methyl benzoate at a similar rate to the homogeneous catalyst (0.0025 mol% catalyst, 10 mol% KOtBu, 80 °C, 50 bar, THF, 21 h, ~15000 turnovers during the first 1 h). The catalyst was used five times for a total of 121680 turnovers. A study on the reusability of this catalyst showed that ester hydrogenations with bifunctional catalysts slow down as the reaction proceeds. This inhibition is removed by isolating and reusing the catalyst, suggesting that future catalyst design should emphasize avoiding product inhibition.
  The trans-2,3-Diaminonorborn-5-ene dihydrochloride was resolved using L-menthol as the chiral auxiliary. Four PNNP ligands and their Ru catalyst monomers were synthesized using this resolved precursor. These four catalyst monomers and their alt-ROMP polymers were studied as enantioselective catalysts in the transfer hydrogenation of acetophenone from 2-PrOH (0.5 mol% catalyst, 0.25 mol% KOtBu, rt–45 °C, 2-PrOH) and in the hydrogenation of β-chiral esters via dynamic kinetic resolution (2–2.5 mol% catalyst, 50 mol% NaOiPr, rt, THF, 4 bar H2); moderate ee’s (up to 52%) were obtained within these catalyses.
  A base-stable cationic monomer, 4-[6-azonia-spiro[5.5]undecyl]-4-azatricyclo-[5.2.1.02,6]dec-8-ene-3,5-dione tetrafluoroborate, was designed and synthesized. This monomer (2 equiv.) was copolymerized with RuCl2(N,N'-bis{2-(diphenylphosphino)benzyl}-bicyclo[2.2.1]hept-5-ene-2,3-diamine) and COE (3 equiv.) via ROMP by a sequential addition method catalyzed by 0.1 equiv. RuCl2(=CHPh)(PCy3)2. The resulting polymeric catalyst contains cationic moieties close to the catalyst metal center and it was immobilized via ROMP over BaSO4 by addition of extra COE and the crosslinker, 1,2-N-di(cis-5-norbornene-2,3-endo-dicarboximido)-ethane. It was anticipated that the cationic moiety holds an alkoxide counterion in a reusing ester hydrogenation, which provides a higher local concentration of base that facilitates the hydrogenation. This hypothesis was examined in the hydrogenation of methyl benzoate (S/C = 4200/1, 50 bar H2, rt, 22 h, THF) in the absence of excess base. The results imply that the proposed local-base assistance does not exist within the current system.
  Glancing Angle Deposition (GLAD) was used to prepare 500 nm long Ni nanopillars directly on glassy carbon disc electrodes (NiGLAD/GC). NiGLAD[Pt]/GC core-layer nanopillars were prepared by depositing Pt on the NiGLAD substrate via a novel rotating disc electrode galvanostatic deposition, where a stationary blackened Pt counter electrode served as the Pt source. Scanning electron microscopy, cyclic voltammetry, and inductively-coupled mass spectrometry were employed to characterize the deposits. The results indicated that the Pt was deposited in a conformal manner on the NiGLAD giving a loading of 11.6 μg. The NiGLAD[Pt]/GC electrode was about three fold more active than a [Pt]/GC (made with the same deposition in the absence of Ni) towards the oxygen reduction reaction (ORR) in 1.0 M KOH. As well, long term potentiostatic ORR studies showed that the NiGLAD[Pt]/GC deposit was more durable than the [Pt]/GC, with the former completely retaining its initial performance after 5000 s polarization at 0.85 V vs. RHE, while [Pt]/GC lost 38% of its activity. Subsequent control experiments in the absence of O2 showed that such decay was not due to loss of Pt over the prolonged ORR.

• Subjects / Keywords

  • Catalysis
  • ORR
  • Ester hydrogenation

• Graduation date

  Fall 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-90tt-c460

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.