Stephanie Kwon | UC Berkeley (original) (raw)

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Papers by Stephanie Kwon

Research paper thumbnail of Chiral Co(II) Metal–Organic Framework in the Heterogeneous Catalytic Oxidation of Alkenes under Aerobic and Anaerobic Conditions

ACS Catalysis, 2014

ABSTRACT The chiral Co(II) MOF [Co(l-RR)(H2O)·H2O]∞ [1; l-RR = (R,R)-thiazolidine-2,4-dicarboxyla... more ABSTRACT The chiral Co(II) MOF [Co(l-RR)(H2O)·H2O]∞ [1; l-RR = (R,R)-thiazolidine-2,4-dicarboxylate] has been exploited in the catalytic oxidation of different alkenes (cyclohexene, (Z)-cyclooctene, 1-octene) using either tert-butyl hydroperoxide (tBuOOH) or molecular oxygen (O2) as oxidants. Different chemoselectivities are observed, both substrate- and oxidant-dependent. A moderate enantioselectivity is also obtained in the case of prochiral precursors, revealing the chiral induction ability of the optically pure metal environment. The interaction of O2 with the exposed metal sites in 1 (after material preactivation and consequent removal of the coordinated aquo ligand) has been studied through TPD-MS analysis combined with DFT calculations, with the aim of probing effective oxygen uptake by the heterogeneous catalyst and unraveling the nature of the active species in the catalytic oxidation process under aerobic conditions. Theoretical results indicate the presence of an η1-superoxo species at the cobalt center, with concomitant Co(II) ↔ Co(III) oxidation. Finally, the experimental estimation of the O2 adsorption enthalpy is found to be in good agreement with the calculated binding energy.

Research paper thumbnail of Vapor-Phase Metalation by Atomic Layer Deposition in a Metal–Organic Framework

Journal of the American Chemical Society, 2013

Research paper thumbnail of A kinetic study of vapor-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1

Journal of Catalysis, 2015

ABSTRACT A kinetic analysis of gas-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1 was... more ABSTRACT A kinetic analysis of gas-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1 was performed. The production of cyclohexene oxide was very stable with high selectivity. Based on the kinetic analysis, the gas-phase mechanism is proposed to be similar to that of the liquid-phase reaction: an Eley–Rideal type mechanism, in which the reaction between a Ti–OOH intermediate and the physisorbed alkene is the rate-determining step. When the partial pressure of water or H2O2 was varied, a compensation effect was observed. Based on the kinetic model, the compensation effect is attributed to variations in the surface coverage of intermediates, specifically the competitive adsorption of water and H2O2 at the Ti active sites. A meaningful activation energy can only be obtained at high surface coverages of H2O2 and was determined to be 40 ± 2 kJ/mol.

Research paper thumbnail of Chiral Co(II) Metal–Organic Framework in the Heterogeneous Catalytic Oxidation of Alkenes under Aerobic and Anaerobic Conditions

ACS Catalysis, 2014

ABSTRACT The chiral Co(II) MOF [Co(l-RR)(H2O)·H2O]∞ [1; l-RR = (R,R)-thiazolidine-2,4-dicarboxyla... more ABSTRACT The chiral Co(II) MOF [Co(l-RR)(H2O)·H2O]∞ [1; l-RR = (R,R)-thiazolidine-2,4-dicarboxylate] has been exploited in the catalytic oxidation of different alkenes (cyclohexene, (Z)-cyclooctene, 1-octene) using either tert-butyl hydroperoxide (tBuOOH) or molecular oxygen (O2) as oxidants. Different chemoselectivities are observed, both substrate- and oxidant-dependent. A moderate enantioselectivity is also obtained in the case of prochiral precursors, revealing the chiral induction ability of the optically pure metal environment. The interaction of O2 with the exposed metal sites in 1 (after material preactivation and consequent removal of the coordinated aquo ligand) has been studied through TPD-MS analysis combined with DFT calculations, with the aim of probing effective oxygen uptake by the heterogeneous catalyst and unraveling the nature of the active species in the catalytic oxidation process under aerobic conditions. Theoretical results indicate the presence of an η1-superoxo species at the cobalt center, with concomitant Co(II) ↔ Co(III) oxidation. Finally, the experimental estimation of the O2 adsorption enthalpy is found to be in good agreement with the calculated binding energy.

Research paper thumbnail of Vapor-Phase Metalation by Atomic Layer Deposition in a Metal–Organic Framework

Journal of the American Chemical Society, 2013

Research paper thumbnail of A kinetic study of vapor-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1

Journal of Catalysis, 2015

ABSTRACT A kinetic analysis of gas-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1 was... more ABSTRACT A kinetic analysis of gas-phase cyclohexene epoxidation by H2O2 over mesoporous TS-1 was performed. The production of cyclohexene oxide was very stable with high selectivity. Based on the kinetic analysis, the gas-phase mechanism is proposed to be similar to that of the liquid-phase reaction: an Eley–Rideal type mechanism, in which the reaction between a Ti–OOH intermediate and the physisorbed alkene is the rate-determining step. When the partial pressure of water or H2O2 was varied, a compensation effect was observed. Based on the kinetic model, the compensation effect is attributed to variations in the surface coverage of intermediates, specifically the competitive adsorption of water and H2O2 at the Ti active sites. A meaningful activation energy can only be obtained at high surface coverages of H2O2 and was determined to be 40 ± 2 kJ/mol.

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