Active electronic states of silver catalysts for methanol selective oxidation

Pestryakov, Alexey; Давыдов, А. А.

doi:10.1016/0926-860x(94)80330-7

Cited by 40 publications

(43 citation statements)

References 5 publications

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“…For the 1 at% Ag/ZrO 2 material, increased absorption intensity compared to the zirconia is observed at $290 and $400 nm. The presence of the Ag d n clusters gives rise to absorption bands at 280 and 380 nm [38,45,46]. These bands can be tentatively assigned to the small oxidized Ag clusters.…”

Section: Catalyst Characterizationmentioning

confidence: 88%

“…The absorption band at 300 nm observed in the spectra of Ag (16)-ZSM-5 may be due to the presence of reduced Ag clusters [49,50] or silver ®lm-like structure [45,46]. The absorption band at the 450 nm can be associated with the small metallic Ag particles located inside the zeolite cages or with the larger Ag particles located on the outside surface [45,46,52]. This band disappears after exposure to oxygen at 3008C [44], con®rming the presence of reduced Ag species.…”

Section: Catalyst Characterizationmentioning

confidence: 99%

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Deep oxidation of methane over zirconia supported Ag catalysts

Kundakovic

Flytzani‐Stephanopoulos

1999

Applied Catalysis A: General

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Zirconia supported silver catalysts were studied for deep oxidation of methane. The catalyst structure was examined by XRD, XPS, STEM-EDX, HR-TEM and UV±Vis spectroscopy and related to the catalyst activity. Methane conversion strongly depends on Ag state and dispersion. At low Ag loading (<2 at%), small Ag particles (<5 nm) have low activity. The turnover frequency for methane oxidation increases as the Ag particle size increases from 5 to 10 nm as determined from HRTEM, while the activation energy remains the same. Ag ion-exchanged ZSM-5 zeolite materials, containing Ag in highly dispersed state as isolated Ag were studied for comparison. High conversion of methane was found only in zeolite catalysts containing a large amount of silver, some of which was in particle form. The reaction rate on zirconia-supported Ag particles is 0.77 order in methane and 0.37 order in oxygen. The reaction products, carbon dioxide and water, do not affect the methane oxidation rate in levels up to of 1.7 and 3.5 mol% in the feedgas, respectively. The active phase under reaction conditions for both low and high Ag loading is the oxygen covered metallic Ag surface, as was con®rmed by XPS and UV±Vis spectrometry. # 1999 Elsevier Science B.V. All rights reserved.

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Section: Catalyst Characterizationmentioning

confidence: 88%

Section: Catalyst Characterizationmentioning

confidence: 99%

Deep oxidation of methane over zirconia supported Ag catalysts

Kundakovic

Flytzani‐Stephanopoulos

1999

Applied Catalysis A: General

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“…Also these sites retard the surface diffusion and aggregation of the metal during the process of methanol oxidation. We observed these effects earlier when studying modified Ag/pumice catalysts [17][18][19]. The same modifying action is expected on the foam-ceramic support.…”

Section: Resultsmentioning

confidence: 61%

“…It means that the modifiers exert a direct effect on the state of silver active sites. Previous studies revealed stabilizing effect of Ce and Zr oxides on ionic states of silver (Ag + , Ag n δ+ ) on the surface of the modified supports [17][18][19][20]. In contrast, additives of La 2 O 3 reduced the amount of ions and their effective charge.…”

Section: Resultsmentioning

confidence: 99%

“…Supported catalysts for formaldehyde synthesis have low surface area (0.5-1 m 2 /g) and high metal percentage, therefore, average size of the metal particles is rather big -more then 1000 nm. However, our previous studies disclosed that even at high silver content a major part of support surface (20-40%) is not covered with the metal film and big aggregates but contains high-dispersed Ag + and Ag n δ+ particles [17][18][19]. These states experience direct effect of the support and modifiers.…”

Section: Resultsmentioning

confidence: 99%

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Alcohol selective oxidation over modified foam-silver catalysts

2004

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Catalysts based on silver supported on foam ceramics and modified by Zr, Ce and La oxides have been studied in the process of partial oxidation of methanol to formaldehyde. The foam catalysts exhibit high catalytic, mechanical and fluidodynamic properties exceeding the characteristics of conventional crystalline and supported silver samples. Modifying additives of Zr and Ce oxides raise activity and selectivity of the supported foam-silver catalyst as well as its stability during the prolonged functioning. The modifiers change the electronic state and redox properties of silver, the metal dispersivity, surface diffusion and aggregation of silver during the long-term service.

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Novel microfibrous‐structured silver catalyst for high efficiency gas‐phase oxidation of alcohols

et al. 2009

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Novel microfibrous-structured silver catalysts were developed for gas-phase selective oxidation of mono-/aromatic-/di-alcohols. Sinter-locked three-dimensional microfibrous networks consisting of 5 vol % 8-lm-Ni (or 12-lm-SS-316L) fibers and 95 vol % void volume were built up by the papermaking/sintering processes. Silver was then deposited onto the surface of the sinter-locked fibers by incipient wetness impregnation method. At relatively low temperatures (e.g., 380C), the microfibrous-structured silver catalysts provided quite higher activity/selectivity compared to the electrolytic silver. The microfibrous Ag/Ni-fiber offered much better low-temperature activity than the Ag/ SS-fiber. The interaction at Ag particles and Ni-fiber interface not only visibly increased the active/selective sites of Ag þ ions and Ag n dþ clusters but also significantly promoted their low-temperature reducibility and ability for O 2 activation. In addition, the microfibrous structure provided a unique combination of large void volume, entirely open structure, high thermal conductivity and high permeability. V

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Active electronic states of silver catalysts for methanol selective oxidation

Cited by 40 publications

References 5 publications

Deep oxidation of methane over zirconia supported Ag catalysts

Deep oxidation of methane over zirconia supported Ag catalysts

Alcohol selective oxidation over modified foam-silver catalysts

Novel microfibrous‐structured silver catalyst for high efficiency gas‐phase oxidation of alcohols

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