Infrared study of nitrogen adsorption on alumina

Zubkov, S. A.; Borovkov, V. Yu.; Gagarin, S. G.; Kazansky, V.B.

doi:10.1016/0009-2614(84)85140-4

Cited by 26 publications

(41 citation statements)

References 9 publications

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“…Zubkov and co-workers demonstrated in the 1980s [26] that g-alumina was able to form ad initrogen complex with molecular nitrogen after thermal dehydration, exhibiting the N-N stretching band at 2360 cm À1 .Coperet et al,later stated that N 2 is as elective probe for 3-coordinate Al 3+ sites that form upon dehydroxylation of the tetrahedral O 3 -Al IV -OH sites on the (110) facet, which coincides with the formation of ab and at 2355 cm À1 .I tw as later suggested that such tricoordinate Al 3+ ions anchored organometallic fragments and produced active catalysts while organometallic fragments anchored on other Al 3+ sites did not produce active catalysts. [15,16,18] However,t hese studies suffered from inaccurate structural representation in the models employed, casting doubt on the conclusions drawn.…”

Section: Angewandte Chemiementioning

confidence: 99%

“…This observation accounts for the lower activity of the 200 8 8C calcined alumina relative to the 500 8 8Cc alcined alumina for ethanol dehydration. [26] (Wer ecommend that all alumina samples be pre-treated at least at % 300 8 8Cinflowing air prior to measuring alcohol dehydration (and activity in other catalytic reactions) in order to evaluate catalytic activity. Otherwise,apart of the surface remains covered by carbon dioxide and potentially other impurities).…”

Section: Angewandte Chemiementioning

confidence: 99%

“…Zubkov and co‐workers demonstrated in the 1980s [26] that γ‐alumina was able to form a dinitrogen complex with molecular nitrogen after thermal dehydration, exhibiting the N‐N stretching band at 2360 cm −1 . Coperet et al., later stated that N 2 is a selective probe for 3‐coordinate Al 3+ sites that form upon dehydroxylation of the tetrahedral O 3 ‐Al IV ‐OH sites on the (110) facet, which coincides with the formation of a band at 2355 cm −1 .…”

Section: Introductionmentioning

confidence: 99%

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Precise Identification and Characterization of Catalytically Active Sites on the Surface of γ‐Alumina**

et al. 2021

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g-alumina is one of the oldest and most important commercial catalytic materials with high surface area and stability.These attributes enabled its use as the first commercial large-scale heterogeneous catalyst for ethanol dehydration. Despite progress in materials characterization the nature of the specific sites on the surface of g-alumina that are responsible for its unique catalytic properties has remained obscure and controversial. By using combined infrared spectroscopy, electron microscopya nd solid-state nuclear magnetic resonance measurements we identify the octahedral, amphoteric (O) 5 Al(VI)-OH sites on the (100) segments of massively restructured (110) facets on typical rhombus-platelet g-alumina as well as the (100) segments of irrational surfaces (invariably always present in all g-alumina samples) responsible for its unique catalytic activity.Such (O) 5 Al(VI)-OH sites are also present on the macroscopically defined (100) facets of g-alumina with elongated/rod-like geometry.T he mechanism by which these sites lose -OH groups upon thermal dehydroxylation resulting in coordinatively unsaturated penta-coordinate Al +3 O 5 sites is clarified. These coordinatively unsaturated penta-coordinate Al sites produce well-defined thermally stable Al-carbonyl complexes.O ur findings contribute to the understanding of the nature of coordinatively unsaturated Al sites on the surface of g-alumina and their role as catalytically active sites.

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Section: Angewandte Chemiementioning

confidence: 99%

Section: Angewandte Chemiementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Precise Identification and Characterization of Catalytically Active Sites on the Surface of γ‐Alumina**

et al. 2021

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“…This enhanced reactivity suggests that Cu sites are located in close proximity to surface Al III defective sites. [ 35 , 36 , 37 ]…”

Section: Resultsmentioning

confidence: 99%

Methane‐to‐Methanol on Mononuclear Copper(II) Sites Supported on Al₂O₃: Structure of Active Sites from Electron Paramagnetic Resonance**

et al. 2021

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The selective conversion of methane to methanol remains one of the holy grails of chemistry, where Cu‐exchanged zeolites have been shown promote this reaction under stepwise conditions. Over the years, several active sites have been proposed, ranging from mono‐, di‐ to trimeric CuII. Herein, we report the formation of well‐dispersed monomeric CuII species supported on alumina using surface organometallic chemistry and their reactivity towards the selective and stepwise conversion of methane to methanol. Extensive studies using various transition alumina supports combined with spectroscopic characterization, in particular electron paramagnetic resonance (EPR), show that the active sites are associated with specific facets, which are typically found in γ‐ and η‐alumina phase, and that their EPR signature can be attributed to species having a tri‐coordinated [(Al2O)CuIIO(OH)]− T‐shape geometry. Overall, the selective conversion of methane to methanol, a two‐electron process, involves two monomeric CuII sites that play in concert.

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“…This enhanced reactivity suggests that Cu sites are located in close proximity to surface AlIII defective sites. [31][32][33] Low-temperature CW EPR, and simulation of the EPR parameters, was performed for 1500-h-a500, which possesses the highest fraction of reactive site I. The EPR spectra of the activated and reacted material for 1500-h-a500 (Fig.…”

Section: Reactivity Of the Materialsmentioning

confidence: 99%

CH4-to-CH3OH on Mononuclear Cu(II) Sites Supported on Al2O3: Structure of Active Sites from Electron Paramagnetic Resonance

Meyet¹,

Ashuiev²,

Noh³

et al. 2021

Preprint

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The selective conversion of methane to methanol remains one of the holy grails of chemistry, where Cu-exchanged zeolites have been shown to selectively convert methane to methanol under stepwise conditions. Over the years, several active sites have been proposed, ranging from mono-, di- to trimeric Cu(II). Herein, we report the formation of well-dispersed monomeric Cu(II) species supported on alumina using surface organometallic chemistry and their reactivity towards the selective and stepwise conversion of methane to methanol. Extensive studies using various transition alumina supports combined with spectroscopic characterization, in particular electron paramagnetic resonance (EPR), show that the active sites are associated with specific facets, which are typically found in gamma- and eta-alumina phase, and that their EPR signature can be attributed to species having a tri-coordinated [(Al2O)CuIIO(OH)]-,T-shape geometry. Overall, the selective conversion of methane to methanol, a two-electron process, involve two of these isolated monomeric Cu(II) sites that play in concert.

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Infrared study of nitrogen adsorption on alumina

Cited by 26 publications

References 9 publications

Precise Identification and Characterization of Catalytically Active Sites on the Surface of γ‐Alumina**

Precise Identification and Characterization of Catalytically Active Sites on the Surface of γ‐Alumina**

Methane‐to‐Methanol on Mononuclear Copper(II) Sites Supported on Al₂O₃: Structure of Active Sites from Electron Paramagnetic Resonance**

CH4-to-CH3OH on Mononuclear Cu(II) Sites Supported on Al2O3: Structure of Active Sites from Electron Paramagnetic Resonance

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Infrared study of nitrogen adsorption on alumina

Cited by 26 publications

References 9 publications

Precise Identification and Characterization of Catalytically Active Sites on the Surface of γ‐Alumina**

Precise Identification and Characterization of Catalytically Active Sites on the Surface of γ‐Alumina**

Methane‐to‐Methanol on Mononuclear Copper(II) Sites Supported on Al2O3: Structure of Active Sites from Electron Paramagnetic Resonance**

CH4-to-CH3OH on Mononuclear Cu(II) Sites Supported on Al2O3: Structure of Active Sites from Electron Paramagnetic Resonance

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Methane‐to‐Methanol on Mononuclear Copper(II) Sites Supported on Al₂O₃: Structure of Active Sites from Electron Paramagnetic Resonance**