Active Ag species in MFI zeolite for direct methane conversion in the light and dark

Yoshida, Hisao; Hamajima, Toyokazu; Kato, Yuko; Shibata, Junji; Satsuma, Atsushi; Hattori, Tadashi

doi:10.1163/156856703322601898

Cited by 22 publications

(34 citation statements)

References 28 publications

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“…5). This is also consistent with previous research 35,36 , reporting small amounts of ethane forming from methane over silver-containing zeolites. The amounts of ethane, propane and carbon dioxide produced over the silver-titania nanocomposite containing different heteropolyacids as a function of reaction time are shown in Supplementary Fig.…”

Section: Photochemical Coupling Of Methane Over Metal Nanocompositessupporting

confidence: 93%

Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature

et al. 2020

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Methane activation and utilization are among the major challenges of modern science. Methane is potentially an important feedstock for manufacturing value-added fuels and chemicals. However, most of known processes require excessive operating temperatures and exhibit insufficient selectivity. Here, we demonstrate a photochemical looping strategy for highly selective stoichiometric conversion of methane to ethane at ambient temperature over silverheteropolyacid-titania nanocomposites. The process involves stoichiometric reaction of methane with highly-dispersed cationic silver under illumination, which results in the formation of methyl radicals. Recombination of the generated methyl radicals leads to selective, and almost quantitative, formation of ethane. Cationic silver species are simultaneously reduced to metallic silver. The silver-heteropolyacid-titania nanocomposites can be reversibly regenerated in air under illumination at ambient temperature. The photochemical looping process achieves methane coupling selectivity over 90%, quantitative yield of ethane over 9%, high quantum efficiency (3.5% at 362 nm) and excellent stability.

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Section: Photochemical Coupling Of Methane Over Metal Nanocompositessupporting

confidence: 93%

Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature

et al. 2020

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“…For example, although TiO 2 photocatalysts produced ethane from methane, it could not produce hydrogen; probably hydrogen would be consumed in reduction of TiO 2 [34,35]. Also in the case of Ag + ionexchanged zeolite that is reported as photocatalyst for other reactions [37], only hydrocarbons such as ethane could be produced upon photoirradiation without formation of hydrogen molecules while Ag þ n clusters were formed at the expense of Ag + exchanged ions, which means that hydrogen was consumed in the reduction of Ag + ions to Ag þ n clusters [38,39]. In order to develop the photocatalytic systems for non-oxidative reaction, the stability of the catalyst in such condition must be considered.…”

Section: Development Of Quantum Photocatalystsmentioning

confidence: 99%

Active sites of silica-based quantum photocatalysts for non-oxidative reactions

Yoshida

2005

Catal Surv Asia

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Various photocatalytic reactions have been developed in recent years. Among them, non-oxidative reactions by silica-based quantum photocatalysts are quite unique. Pure silica materials, especially mesoporous silica evacuated at high temperature, were found to promote olefin metathesis upon photoirradiation at room temperature. A kind of surface defect on silica was generated through dehydroxylation at high temperature before the photoreaction, which can be photoexcited to form the first surface intermediate. On the other hand, non-oxidative direct methane coupling was revealed to proceed on silica materials and silica-based quantum photocatalysts. Also in these cases, evacuation at high temperature was required for the activation of catalyst before the reaction. The active sites and feature of silica-based quantum photocatalysts for these non-oxidative reaction systems are summarized and discussed.

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“…This category includes H + and the monovalent Lewis acids (Li + , Na + , Ag + ). The active site for Ag‐ZSM‐5 for hydrocarbon upgrade has been characterized to be in the form of Ag + cations or Ag n clusters . While the presence of Ag clusters cannot be ruled out without further investigation, we chose Ag + as the active site.…”

Section: Resultsmentioning

confidence: 99%

“…The active site for Ag-ZSM-5 for hydrocarbon upgrade has been characterized to be in the form of Ag + cations [46][47][48] or Ag n clusters. [49][50][51] While the presence of Ag clusters cannot be ruled out without further investigation, we chose Ag + as the active site. Li + and Na + cations are also assumed to be analogous monovalent active sites.…”

Section: Preferred Activation Pathwaysmentioning

confidence: 99%

Quantification and Statistical Analysis of Errors Related to the Approximate Description of Active Site Models in Metal‐Exchanged Zeolites

2019

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Metal‐exchanged zeolites are complex catalytic systems with great potential for applications in hydrocarbon conversion processes. The numerous combinations of zeotypes and metal‐based Lewis acid motifs create a vast material space that can only be effectively navigated with robust structure‐function relationships. Exhaustive modeling of extraframework metal sites in all crystallographically distinct framework positions is not practical; thus, we quantified the uncertainties arising from the use of simplified active site representations using the C−H bond activation in methane as a probe reaction. Density functional theory calculations and statistical analysis of associated error ensembles suggest that the Lewis acid identity primarily determines the reactivity of the zeolite towards methane activation, with other factors such as zeolite model characteristics deemed secondary. The error ensemble distributions were used to predict the relative probability of creating active C−H bond scission fragments in metal‐exchanged zeolites, and thus can be used to efficiently screen various metal‐exchange candidates in their efficacy towards hydrocarbon conversion.

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Active Ag species in MFI zeolite for direct methane conversion in the light and dark

Cited by 22 publications

References 28 publications

Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature

Stoichiometric methane conversion to ethane using photochemical looping at ambient temperature

Active sites of silica-based quantum photocatalysts for non-oxidative reactions

Quantification and Statistical Analysis of Errors Related to the Approximate Description of Active Site Models in Metal‐Exchanged Zeolites

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