Chemisorption of hydrogen on Ag-Y studied by 1H MAS NMR

Baba, Toshihide; Komatsu, Norito; Takahashi, Takehiro; Sugisawa, Hisashi; Ono, Yoshio

doi:10.1016/s0167-2991(99)80223-7

Cited by 7 publications

(7 citation statements)

References 10 publications

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“…56 However, the high mobility of the protons in the Keggin structure prevents establishing unequivocal correlations between the chemical shift of the protons in HPA and their acid strength. 57 The 1 H NMR spectra of bulk and supported HPAs are shown in Fig. 6.…”

Section: Catalysis Science and Technology Papermentioning

confidence: 99%

TiO₂-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

Ladera

Ojeda

Fierro

et al. 2015

Catal. Sci. Technol.

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Two heteropoly acids (HPAs) with Keggin structures, namely, H 3 PW 12 O 40 (HPW) and H 4 SiW 12 O 40 (HSiW), have been deposited on TiO 2 and used as catalysts for the production of dimethyl ether (DME) from methanol. The catalysts have been prepared by incipient wetness impregnation of HPW and HSiW on TiO 2 with HPA loadings ranging between 0.9 and 9.0 Keggin units (KU) per square nanometer. The structure and acid properties of the final catalysts have been thoroughly characterized by N 2 adsorption-desorption isotherms, TGA, XRD, Raman spectroscopy, XPS, NH 3 adsorption isotherms, DRIFT and 1 H NMR. All catalysts exhibit very high DME productivities and high methanol conversion rates at temperatures as low as 413 K. The effect of the HPA loading on TiO 2 for the production of DME has been correlated with the structure and acid properties of the final catalyst. We find an optimum loading for both TiO 2 -supported HPW and HSiW of 2.3 KU nm −2 . At this level, both HPW and HSiW are well dispersed onto the support, thus permitting the access of methanol to the active acid sites. On the contrary, higher HPA loadings on TiO 2 result in the formation of larger HPA units that prevent the access of methanol to the inner acid sites within the HPA. On the other hand, HPA loadings below 2.3 KU nm −2 result in a strong interaction between the acid protons of the HPAs and the support, hence preventing the participation of such protons in the methanol dehydration reaction, which results in lower methanol conversion rates.

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Section: Catalysis Science and Technology Papermentioning

confidence: 99%

TiO₂-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

Ladera

Ojeda

Fierro

et al. 2015

Catal. Sci. Technol.

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“…It provided unequivocal evidence for the heterolytic dissociation of hydrogen over Ag n + in Ag-A and Ag-Y [33][34][35]. Figure 1 shows the 1 H MAS NMR spectrum for Ag-A under hydrogen (40 kPa) after the reduction with hydrogen at 313 K for 30 min.…”

Section: Heterolytic Dissociation Of Hydrogen Over Ag-a and Ag-y Zeolmentioning

confidence: 92%

Conversion of Methane over Ag+-exchanged Zeolite in the Presence of Ethene

Baba

2005

Catal Surv Asia

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Methane is shown to react with ethene over silver-exchanged zeolites at around 673 K to form higher hydrocarbons. Methane conversion of 13.2% is achieved at 673 K over Ag-ZSM)5 catalyst. Under these conditions, H-ZSM)5 does not catalyze the methane conversion, only ethene being converted into higher hydrocarbons. Zeolites with extra-framework metal cations such as In and Ga also activate methane in the presence of ethene. Using 13 C-labeled methane as a reactant, propene is shown to be a primary product from methane and ethane. 13 C atoms were not found in benzene molecules produced, indicating that benzene is entirely originated from ethane. On the other hand, in toluene, 13 C atoms are found in both the methyl group and the aromatic ring. This implies that toluene is formed by the reaction of propene with butenes formed by the dimerization of ethene, and also by the reaction of benzene with methane. The latter path was confirmed by direct reaction of 13 CH 4 with benzene. In this case, 13 C atoms are found only in methyl groups of toluene produced. The heterolytic dissociation of methane over Ag + -exchanged zeolites is proposed as a reaction mechanism for the catalytic conversion of methane, leading to the formation of silver hydride and CH 3 d+ species, which reacts with ethene and benzene to form propene and toluene, respectively. The conversion of methane over zeolites loaded with metal cations other than Ag + is also described. The reaction of methane with benzene over indium-loaded ZSM)5 afforded toluene and xylenes in yields of up to 7.6% and 0.9% at 623 K when the reaction was carried out in a flow reactor.

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“…The product distribution indicated that pentenes (or their precursor carbenium ions) formed by reaction (25) readily decompose into propene and ethene. 75 The rate of each reaction could be determined from the yields of hydrogen or alkanes.…”

Section: Mechanism Of Activation Of Lower Alkanesmentioning

confidence: 99%

“…4 shows the change in the intensities of the three peaks with the degree of reduction of Ag + ions. 25 The degree of Ag + ion reduction was changed by changing the reduction time under 40 kPa of H 2 at 473 K. The amount of both bridged OH groups increased with Ag + ion reduction. At a low reduction degree, the OH groups in the supercage are mainly formed, and the OH groups in the sodalite cage grow up at the later stage.…”

Section: Introductionmentioning

confidence: 97%

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Unique properties of silver cations in solid-acid catalysis by zeolites and heteropolyacids

Ono

Baba

2015

Phys. Chem. Chem. Phys.

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Ag(+)-exchanged zeolites exhibit unique catalytic properties caused by the combination of their redox and acidic properties. Partial reduction of Ag(+) ions in zeolites with hydrogen leads to the formation of acidic protons and silver metal particles, which can be observed using X-ray powder diffraction patterns (XRD). By simply evacuating hydrogen from the system, the silver metal particles are returned back to Ag(+) ions and at the same time, acidic protons are eliminated. This interconversion of Ag(+) ions and silver metal or gaseous hydrogen and surface protons is reflexed in the catalytic activities of Ag(+)-exchanged zeolites for acid-catalyzed reactions: the activity of Ag(+)-exchanged Y zeolite (Ag-Y) reversibly changes with the partial pressure of hydrogen. Furthermore, the activity of Ag-Y in the presence of hydrogen is higher than that of H(+)-exchanged Y zeolite (H-Y). Similar phenomena are also observed for the silver salt of dodecatungstophosphoric acid (Ag3PW12O40). Ag(+)-exchanged ZSM-5 zeolite (Ag-ZSM-5) is a very selective catalyst for aromatization of alkanes, alkenes and methanol. Examination of the activation step of lower alkanes revealed that Ag(+) ions dramatically enhance the dehydrogenation of the alkanes via heterolytic dissociation of the alkanes into carbenium ions and hydride species. Ag(+)-exchanged zeolites can also activate methane. The reaction of methane with ethene and benzene gives propene and toluene, respectively. Ag-ZSM-5 is a very stable catalyst under hydrothermal conditions because of the interconversion properties of Ag(+) ions and silver metal in the zeolite.

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Chemisorption of hydrogen on Ag-Y studied by 1H MAS NMR

Cited by 7 publications

References 10 publications

TiO₂-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

TiO₂-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

Conversion of Methane over Ag+-exchanged Zeolite in the Presence of Ethene

Unique properties of silver cations in solid-acid catalysis by zeolites and heteropolyacids

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Chemisorption of hydrogen on Ag-Y studied by 1H MAS NMR

Cited by 7 publications

References 10 publications

TiO2-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

TiO2-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

Conversion of Methane over Ag+-exchanged Zeolite in the Presence of Ethene

Unique properties of silver cations in solid-acid catalysis by zeolites and heteropolyacids

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Product

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TiO₂-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction

TiO₂-supported heteropoly acid catalysts for dehydration of methanol to dimethyl ether: relevance of dispersion and support interaction