Oxidation catalysis of unsaturated hydrocarbons with molecular oxygen via single-electron transfer in thermally treated H zeolites

Leu, Thomas M.; Roduner, Emil

doi:10.1016/j.jcat.2004.09.008

Cited by 23 publications

(32 citation statements)

References 36 publications

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“…The structure and composition of the sites needed to generate radical cations have been debated27 vigorously and have been attributed to Lewis acid, redox sites, and BAS. Evidence that indicates that the radical cations are formed by single‐electron redox sites had been reported 28. Our measurements suggest that naphthalene radical cations are formed by redox sites in the dehydroxylated samples.…”

Section: Resultssupporting

confidence: 76%

Polymer Crystallization on the Surface of Water or Aqueous Salt Solution

et al. 2016

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The crystallization of two semicrystalline and water-insoluble polymers with ester moieties, namely poly(e-caprolactone) (PCL) and isotactic poly(methyl methacrylate) (i-PMMA), was studied on the water surface using Langmuir trough measurements and Brewster angle microscopy. Additionally, Langmuir-Blodgett films were prepared and examined by atomic force microscopy. It was demonstrated that PCL forms distinct single crystals on the water surface with polymer chain orientation perpendicular to the water surface. i-PMMA behaved differently and crystallized upon compression on the water surface in a homogeneous layer with polymer chain orientation parallel to the water surface. In contrast, poly(ethylene oxide) (PEO) is a water-soluble polyether and its crystallization at the air/liquid interface could only be studied when the water subphase was replaced with aqueous salt solutions containing kosmotropic salts according to the Hofmeister series.

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Section: Resultssupporting

confidence: 76%

Polymer Crystallization on the Surface of Water or Aqueous Salt Solution

et al. 2016

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“…Evidence that indicates that the radical cations are formed by single-electron redox sites had been reported. [28] Our measurements suggest that naphthalene radical cations are formed by redox sites in the dehydroxylated samples. After oxygen treatment, it is possible that Lewis acid sites are responsible for the formation of naphthalene radical cations, be-cause the propane product distribution does not change significantly even though the corresponding radical cations' concentration is high.…”

Section: Effect Of Sample Treatment On Propane Conversion and Selectimentioning

confidence: 68%

High‐Temperature Produced Catalytic Sites Selective for n‐Alkane Dehydrogenation in Acid Zeolites: The Case of HZSM‐5

2011

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The effect of high‐temperature treatment on the catalytic activity and selectivity of two HZSM5 samples has been investigated by using propane activation as the test reaction. The samples have been characterized by using X‐ray powder diffraction, nitrogen adsorption, FTIR spectroscopy, and ammonia temperature‐programmed desorption (TPD). Before high‐temperature treatment, the samples have activation energies and selectivity toward propane cracking versus dehydrogenation comparable with similar samples reported in the literature. After high‐temperature treatment (825 °C in N2), the sample’s microporous and crystalline structure remains nearly intact, but a clear decrease in the number of Brønsted‐acid sites is detected by using FTIR and ammonia TPD. Despite the decrease (≈70 %), the rate of reaction is about the same before and after heating. The selectivity toward dehydrogenation, however, increases by at least a factor of 2, whereas the activation energy for dehydrogenation decreases considerably. This is evidence that new catalytic sites are formed upon dehydroxylation. By using naphthalene as a probe molecule, it is shown that the new sites have the ability to form stable radical cations out of the neutral naphthalene, which suggests that the new sites activate propane by a redox mechanism. The kinetic isotope effect on the rate of dehydrogenation is also consistent with a redox process. The effect of heating in an oxygen atmosphere at lower temperatures was also investigated and only minor effects on reaction rates and selectivity were observed. Naphthalene adsorption experiments on oxygen‐treated samples, however, produce more radical cations than on the samples treated at high temperatures, a result that does not correlate with the dehydrogenation activity of oxygen‐treated samples.

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“…Note that the spontaneous ionization of aromatic molecules with high ionization potential in the gas phase such as biphenyl (PP 2 , I g = 8.16 eV) or benzene (I g = 9.24 eV) is effective only after drastic thermal treatment above 873 K or under O 2 with dehydrogenation of a large fraction of the BAS. [36,37] No such dehydrogenation of the zeolites under study was observed, as indicated by the high IR intensity of the n(OH) stretching mode in diffuse-reflectance infrared Fourier transform (DRIFT) spectra recorded during dehydration up to 723 K (see the Supporting Information).…”

Section: Wwwchemphyschemorgmentioning

confidence: 99%

Effects of Spatial Constraints and Brønsted Acid Site Locations on para‐Terphenyl Ionization and Charge Transfer in Zeolites

et al. 2011

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The locations of Brønsted acid sites (BAS) in the channels of medium-pore zeolites have a significant effect on the spontaneous ionization of para-terphenyl (PP(3)) insofar as spatial constraints determine the stability of transition states and charge-transfer complexes relevant to charge separation. The ionization rates and ionization yield values demonstrate that a strong synergy exists between the H(+) polarization energy and spatial constraints imposed by the channel topology. Spectroscopic and modeling results show that PP(3) incorporation, charge separation, charge transfer and charge recombination differ dramatically among zeolites with respect to channel structure (H-FER, H-MFI, H-MOR) and BAS density in the channel. Compartmentalization of ejected electrons away from the initial site of ionization decreases dramatically the propensity for charge recombination. The main mode of PP(3)(.+) decay is hole transfer to form AlO(4)H(.+) ⋅⋅⋅PP(3) charge-transfer complexes characterized by intense absorption in the visible range. According to the nonadiabatic electron-transfer theory, the small reorganization energy in constrained channels explains the slow hole-transfer rate.

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Oxidation catalysis of unsaturated hydrocarbons with molecular oxygen via single-electron transfer in thermally treated H zeolites

Cited by 23 publications

References 36 publications

Polymer Crystallization on the Surface of Water or Aqueous Salt Solution

Polymer Crystallization on the Surface of Water or Aqueous Salt Solution

High‐Temperature Produced Catalytic Sites Selective for n‐Alkane Dehydrogenation in Acid Zeolites: The Case of HZSM‐5

Effects of Spatial Constraints and Brønsted Acid Site Locations on para‐Terphenyl Ionization and Charge Transfer in Zeolites

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