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Start Over Author "Hunger, Michael" Journal journal of catalysis
20 results on '"Hunger, Michael"'

18. Surface Species Formed during Aniline Methylation on Zeolite H–Y Investigated by in SituMAS NMR Spectroscopy

Author

Ivanova, Irina I, Pomakhina, Elena B, Rebrov, Alexander I, Hunger, Michael, Kolyagin, Yuryi G, and Weitkamp, Jens

Abstract

Aniline alkylation with methanol on zeolite H–Y has been studied using in situ13C MAS NMR spectroscopy under batch conditions. To clarify the main reaction pathways, the conversion of methanol as well as the interaction of aniline with surface methoxy groups were investigated under similar conditions. Methanol-13C and methyl iodide-13C were used as labeled reactants. Co -adsorption of aniline and methanol-13C on zeolite H–Y led to strongly adsorbed aniline molecules, assigned to aniline H-bonded to zeolite Brønsted acid sites, and three types of methanol species of different mobility: mobile methanol molecules with a liquid-like characteristics and two types of rigid methanol species with solid-like characteristics attributed to a methanol adsorption complex with aniline and surface methoxy groups, respectively. Among all the methanol species observed, only surface methoxy groups were shown to be responsible for aniline alkylation which takes place at temperatures from 373 to 523 K. The formation of surface methoxy groups was found to be a limiting step of the overall reaction. The primary alkylation product is N-methylaniline. Toluidines and N-methyltoluidines are formed at temperatures from 523 to 623 K after complete conversion of methanol to N-methylaniline. Therefore, isomerization or disproportionation of N-methylaniline was proposed to account for their formation.

Published
2001
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20. Quantitative solid-state NMR investigation of V5+ species in VPO catalysts upon sequential selective oxidation of n-butane

Author

Frey, Jörg, Lieder, Christian, Schölkopf, Thomas, Schleid, Thomas, Nieken, Ulrich, Klemm, Elias, and Hunger, Michael

Subjects
*VANADIUM catalysts, *PHOSPHORUS, *NUCLEAR magnetic resonance spectroscopy, *SOLID state chemistry, *CATALYST supports, *MESOPOROUS materials, *NITROGEN, *OXIDATION-reduction reaction, *BUTANE, *REACTION mechanisms (Chemistry)
Abstract

Abstract: Bulk VPO catalysts (VPO/bulk) and VPO catalysts supported on mesoporous SBA-15 material (VPO/SBA-15) were treated sequentially in a flow of nitrogen loaded with n-butane and of synthetic air loaded with n-butane in order to reach a complete reduction and reoxidation, respectively, of the catalyst surface. The V5+ species on these VPO catalysts were quantitatively investigated by solid-state NMR spectroscopy and correlated with the catalytic activities of the corresponding materials in the selective oxidation of n-butane to maleic anhydride. By 31P{1H} cross-polarization MAS NMR experiments on the n-butane-loaded VPO/SBA-15 catalyst was evidenced that n-butane is preferentially adsorbed at surface sites of δ-VOPO4-like phases. Based on the number of P/V5+ species in δ-VOPO4-like phases as determined by MAS NMR spectroscopy, the turnover frequency of the surface sites on the VPO/SBA-15 catalyst was estimated to be about 0.2s−1. [Copyright &y& Elsevier]

Published
2010
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