Structure and reactivity of Zn-modified ZSM-5 zeolites : the importance of clustered cationic Zn complexes

S.M.T. Almutairi, B. Mezari, P.C.M.M. Magusin, E.A. Pidko, E.J.M. Hensen

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Abstract

A novel route for the introduction of well-defined zinc species into ZSM-5 zeolite via chemical vapor deposition of dimethylzinc (CVD(DMZ)) is explored. The structural properties and catalytic reactivity of the synthesized material (Zn/ZSM-5-CVD(DMZ)) are investigated against a set of Zn/ZSM-5 catalysts prepared by incipient wetness impregnation (IWI), ion exchange (IE), and high-temperature reaction with zinc vapor (CVD(m)). The materials are characterized by a range of physicochemical methods including temperature programmed reduction (TPR), in situ FTIR, magic-angle spinning (MAS) NMR, and X-ray absorption spectroscopy (XAS). The catalysts are tested for their activity in the dehydrogenation of propane. Catalysts prepared by IE and IWI exhibit a high degree of heterogeneity of extraframework zinc species. These include, besides isolated Zn2+ cations, multinuclear oxygenated zinc clusters and bulk zinc oxide aggregates. The CVD(m) method results in quantitative replacement of all Brønsted acid protons by isolated Zn2+. In CVD(DMZ) the Brønsted acid sites (BAS) react stoichiometrically with dimethylzinc Zn(CH3)2 (DMZ) yielding grafted [Zn-CH3]+ species, which can further be transformed to isolated Zn2+ ions by reduction in hydrogen. The presence of zinc in ZSM-5 enhances the rate of alkane dehydrogenation. The initial activity of Zn/ZSM-5 prepared by IWI and IE correlates with the Zn content. The samples with a more heterogeneous distribution of extraframework Zn species are more active than the samples with isolated Zn2+. The activity of reduced Zn/ZSM-5-CVD(DMZ) containing predominantly isolated Zn2+ ions can be substantially increased by oxidation prior to the reaction. However, the resulting oxygenated complexes easily decompose during the reaction. Propane dehydrogenation and catalyst stability of Zn/ZSM-5-CVD(DMZ) can be improved by addition of steam to the hydrocarbon feed. This rate enhancement is ascribed to an increase of the steady-state concentration of the reactive oxygenated sites.
Original languageEnglish
Pages (from-to)71-83
Number of pages13
JournalACS Catalysis
Volume2
Issue number1
DOIs
Publication statusPublished - 2012

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Zeolites
Chemical vapor deposition
Zinc
Dehydrogenation
Impregnation
Ion exchange
Propane
Catalysts
Ions
Zinc Oxide
Magic angle spinning
X ray absorption spectroscopy
Alkanes
Acids
Steam
Hydrocarbons
dimethylzinc
Zinc oxide
Paraffins
Cations

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@article{014c5a5ec074456182772a6690aa6e08,
title = "Structure and reactivity of Zn-modified ZSM-5 zeolites : the importance of clustered cationic Zn complexes",
abstract = "A novel route for the introduction of well-defined zinc species into ZSM-5 zeolite via chemical vapor deposition of dimethylzinc (CVD(DMZ)) is explored. The structural properties and catalytic reactivity of the synthesized material (Zn/ZSM-5-CVD(DMZ)) are investigated against a set of Zn/ZSM-5 catalysts prepared by incipient wetness impregnation (IWI), ion exchange (IE), and high-temperature reaction with zinc vapor (CVD(m)). The materials are characterized by a range of physicochemical methods including temperature programmed reduction (TPR), in situ FTIR, magic-angle spinning (MAS) NMR, and X-ray absorption spectroscopy (XAS). The catalysts are tested for their activity in the dehydrogenation of propane. Catalysts prepared by IE and IWI exhibit a high degree of heterogeneity of extraframework zinc species. These include, besides isolated Zn2+ cations, multinuclear oxygenated zinc clusters and bulk zinc oxide aggregates. The CVD(m) method results in quantitative replacement of all Br{\o}nsted acid protons by isolated Zn2+. In CVD(DMZ) the Br{\o}nsted acid sites (BAS) react stoichiometrically with dimethylzinc Zn(CH3)2 (DMZ) yielding grafted [Zn-CH3]+ species, which can further be transformed to isolated Zn2+ ions by reduction in hydrogen. The presence of zinc in ZSM-5 enhances the rate of alkane dehydrogenation. The initial activity of Zn/ZSM-5 prepared by IWI and IE correlates with the Zn content. The samples with a more heterogeneous distribution of extraframework Zn species are more active than the samples with isolated Zn2+. The activity of reduced Zn/ZSM-5-CVD(DMZ) containing predominantly isolated Zn2+ ions can be substantially increased by oxidation prior to the reaction. However, the resulting oxygenated complexes easily decompose during the reaction. Propane dehydrogenation and catalyst stability of Zn/ZSM-5-CVD(DMZ) can be improved by addition of steam to the hydrocarbon feed. This rate enhancement is ascribed to an increase of the steady-state concentration of the reactive oxygenated sites.",
author = "S.M.T. Almutairi and B. Mezari and P.C.M.M. Magusin and E.A. Pidko and E.J.M. Hensen",
year = "2012",
doi = "10.1021/cs200441e",
language = "English",
volume = "2",
pages = "71--83",
journal = "ACS Catalysis",
issn = "2155-5435",
publisher = "American Chemical Society",
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}

Structure and reactivity of Zn-modified ZSM-5 zeolites : the importance of clustered cationic Zn complexes. / Almutairi, S.M.T.; Mezari, B.; Magusin, P.C.M.M.; Pidko, E.A.; Hensen, E.J.M.

In: ACS Catalysis, Vol. 2, No. 1, 2012, p. 71-83.

Research output: Contribution to journalArticleAcademicpeer-review

TY - JOUR

T1 - Structure and reactivity of Zn-modified ZSM-5 zeolites : the importance of clustered cationic Zn complexes

AU - Almutairi, S.M.T.

AU - Mezari, B.

AU - Magusin, P.C.M.M.

AU - Pidko, E.A.

AU - Hensen, E.J.M.

PY - 2012

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N2 - A novel route for the introduction of well-defined zinc species into ZSM-5 zeolite via chemical vapor deposition of dimethylzinc (CVD(DMZ)) is explored. The structural properties and catalytic reactivity of the synthesized material (Zn/ZSM-5-CVD(DMZ)) are investigated against a set of Zn/ZSM-5 catalysts prepared by incipient wetness impregnation (IWI), ion exchange (IE), and high-temperature reaction with zinc vapor (CVD(m)). The materials are characterized by a range of physicochemical methods including temperature programmed reduction (TPR), in situ FTIR, magic-angle spinning (MAS) NMR, and X-ray absorption spectroscopy (XAS). The catalysts are tested for their activity in the dehydrogenation of propane. Catalysts prepared by IE and IWI exhibit a high degree of heterogeneity of extraframework zinc species. These include, besides isolated Zn2+ cations, multinuclear oxygenated zinc clusters and bulk zinc oxide aggregates. The CVD(m) method results in quantitative replacement of all Brønsted acid protons by isolated Zn2+. In CVD(DMZ) the Brønsted acid sites (BAS) react stoichiometrically with dimethylzinc Zn(CH3)2 (DMZ) yielding grafted [Zn-CH3]+ species, which can further be transformed to isolated Zn2+ ions by reduction in hydrogen. The presence of zinc in ZSM-5 enhances the rate of alkane dehydrogenation. The initial activity of Zn/ZSM-5 prepared by IWI and IE correlates with the Zn content. The samples with a more heterogeneous distribution of extraframework Zn species are more active than the samples with isolated Zn2+. The activity of reduced Zn/ZSM-5-CVD(DMZ) containing predominantly isolated Zn2+ ions can be substantially increased by oxidation prior to the reaction. However, the resulting oxygenated complexes easily decompose during the reaction. Propane dehydrogenation and catalyst stability of Zn/ZSM-5-CVD(DMZ) can be improved by addition of steam to the hydrocarbon feed. This rate enhancement is ascribed to an increase of the steady-state concentration of the reactive oxygenated sites.

AB - A novel route for the introduction of well-defined zinc species into ZSM-5 zeolite via chemical vapor deposition of dimethylzinc (CVD(DMZ)) is explored. The structural properties and catalytic reactivity of the synthesized material (Zn/ZSM-5-CVD(DMZ)) are investigated against a set of Zn/ZSM-5 catalysts prepared by incipient wetness impregnation (IWI), ion exchange (IE), and high-temperature reaction with zinc vapor (CVD(m)). The materials are characterized by a range of physicochemical methods including temperature programmed reduction (TPR), in situ FTIR, magic-angle spinning (MAS) NMR, and X-ray absorption spectroscopy (XAS). The catalysts are tested for their activity in the dehydrogenation of propane. Catalysts prepared by IE and IWI exhibit a high degree of heterogeneity of extraframework zinc species. These include, besides isolated Zn2+ cations, multinuclear oxygenated zinc clusters and bulk zinc oxide aggregates. The CVD(m) method results in quantitative replacement of all Brønsted acid protons by isolated Zn2+. In CVD(DMZ) the Brønsted acid sites (BAS) react stoichiometrically with dimethylzinc Zn(CH3)2 (DMZ) yielding grafted [Zn-CH3]+ species, which can further be transformed to isolated Zn2+ ions by reduction in hydrogen. The presence of zinc in ZSM-5 enhances the rate of alkane dehydrogenation. The initial activity of Zn/ZSM-5 prepared by IWI and IE correlates with the Zn content. The samples with a more heterogeneous distribution of extraframework Zn species are more active than the samples with isolated Zn2+. The activity of reduced Zn/ZSM-5-CVD(DMZ) containing predominantly isolated Zn2+ ions can be substantially increased by oxidation prior to the reaction. However, the resulting oxygenated complexes easily decompose during the reaction. Propane dehydrogenation and catalyst stability of Zn/ZSM-5-CVD(DMZ) can be improved by addition of steam to the hydrocarbon feed. This rate enhancement is ascribed to an increase of the steady-state concentration of the reactive oxygenated sites.

U2 - 10.1021/cs200441e

DO - 10.1021/cs200441e

M3 - Article

VL - 2

SP - 71

EP - 83

JO - ACS Catalysis

JF - ACS Catalysis

SN - 2155-5435

IS - 1

ER -