Study of Cs-Promoted, α-Alumina-Supported Silver, Ethylene-Epoxidation Catalysts

Epling, William S.; Hoflund, Gar B.; Minahan, David M.

doi:10.1006/jcat.1997.1831

Cited by 40 publications

(16 citation statements)

References 19 publications

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“…The oxygen−silver interaction has been studied extensively − due to the importance of this system in the silver-catalyzed epoxidation of ethylene to ethylene oxide. − Several forms of oxygen have been identified at Ag surfaces including atomic, molecular, and subsurface species as discussed in the review by Van Santen and Kuipers . Studying the O−Ag interaction is complicated further by the presence of contamination which typically exists on air-exposed, as-prepared catalysts or model surfaces.…”

Section: Introductionmentioning

confidence: 99%

Surface Characterization Study of the Thermal Decomposition of Ag₂CO₃

Epling

Hoflund

Salaita³

1998

J. Phys. Chem. B

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The changes in chemical states and composition of the surface region of a Ag2CO3 powder at various stages during thermal decomposition have been examined using X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). The near-surface region of the as-received powder consists primarily of Ag2CO3 although some hydrocarbon and alcohol contaminants also are present. A 155 °C anneal results in partial decomposition of Ag2CO3 to Ag metal and oxides and reduces the amounts of the C contaminants. An anneal at 170 °C causes further decomposition of the Ag2CO3 to Ag metal, Ag2O, and AgO. ISS data indicate that at 205 °C oxygen migrates more rapidly to the outermost atomic layer than it desorbs, resulting in an increased oxygen concentration. The AgO species undergoes further decomposition to Ag2O during a 340 °C anneal treatment. Between 340 and 430 °C the Ag2O decomposes, leaving only Ag metal and subsurface oxygen in the near-surface region of the sample. These results are consistent with temperature-programmed reaction (TPR) data which exhibit a CO2 peak at 260 °C and an O2 peak at 420 °C. Both the XPS and TPR data indicate that the thermal decomposition of these species are activated since their decompositions occur at temperatures much higher than predicted by equilibrium thermodynamic calculations.

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Section: Introductionmentioning

confidence: 99%

Surface Characterization Study of the Thermal Decomposition of Ag₂CO₃

Epling

Hoflund

Salaita³

1998

J. Phys. Chem. B

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“…As shown in the aforementioned results, there were several reactions occurring in the plasma reaction zone so it is not possible to easily carry out the kinetic consideration of the ethylene epoxidation reaction. Future works will then be focused on the combination of the low-temperature DBD system with various reported catalytically active catalysts used in the conventional catalytic process, especially Ag/Al 2 O 3 -based catalysts [5][6][7][8][9][10][11][12][13][14][15]20], aiming to enhance the EO yield. The comparative study of ethylene epoxidation under different kinds of lowtemperature plasma discharges, such as corona discharge system with pin and plate electrodes, is also of our strong interest.…”

Section: Effect Of Electrode Gap Distancementioning

confidence: 99%

“…Since 1940, almost all EO produced industrially has been made using this method [4]. To date, silver catalysts supported on alpha-alumina (Ag/a-Al 2 O 3 ) with alkali and transition metal promoters [5][6][7][8][9][10][11][12][13][14][15], such as Cs, Cu, Re, and Au, or with addition of chlorine-containing moderators into gaseous reactants [16][17][18][19][20], such as dichloroethane (C 2 H 4 Cl 2 ) and vinyl chloride (C 2 H 3 Cl), provide high selectivity for EO. However, the conventional catalytic process normally requires high temperatures, i.e.…”

Section: Introductionmentioning

confidence: 99%

Ethylene Epoxidation in Low-Temperature AC Dielectric Barrier Discharge: Effects of Oxygen-to-Ethylene Feed Molar Ratio and Operating Parameters

Sreethawong

Suwannabart

Chavadej

2008

Plasma Chem Plasma Process

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Ethylene oxide (EO), a valuable chemical feedstock in producing many industrial chemicals, which is industrially produced by the partial oxidation of ethylene, so-called ethylene epoxidation, has been of great interest in many global research studies. In this work, the epoxidation of ethylene under a low-temperature dielectric barrier discharge (DBD) was feasibly investigated to find the best operating conditions. It was experimentally found that the EO yield decreased with increasing O 2 /C 2 H 4 feed molar ratio, feed flow rate, input frequency, and electrode gap distance, while it increased with increasing applied voltage up to 19 kV. The highest EO yield of 5.6% was obtained when an input frequency of 500 Hz and an applied voltage of 19 kV were used, with an O 2 /C 2 H 4 feed molar ratio of 1:1, a feed flow rate of 50 cm 3 /min, and an electrode gap distance of 10 mm. Under these best conditions, the power consumption was found to be as low as 6.07 9 10 -16 Ws/molecule of EO produced.

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“…In addition to this, it has also been suggested that cesium plays a role in binding and dispersing the silver crystals on the catalyst support, as well as increasing the adsorption probability of oxygen on silver [15][16][17][18][19]. According to Minahan and co-workers [20], Cs acts as a binder between the Al 2 O 3 surface and the Ag crystallites to give a more uniform and higher coverage of the Ag component.…”

Section: Introductionmentioning

confidence: 96%

Nano‐sized silver crystals and their dispersion over α‐alumina for ethylene epoxidation

Hassani¹,

Ghasemi²,

Rashidzadeh³

et al. 2009

Cryst. Res. Technol.

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Ethylene oxide catalyst is a high metal loading catalyst, in which silver crystals is impregnated on α-Al 2 O 3 support. In this type of catalyst, metal dispersion plays an important role on catalyst selectivity for desired products. In this work, silver nitrate and silver oxide together with oxalic and lactic acid as the raw materials were used with different impregnation techniques to make catalysts with high silver content and dispersion. It is also known that the use of promoters affect the metal dispersion on the catalyst support and for that cesium was used as the promoter to improve the silver crystal dispersion. Physical and chemical characteristics of the prepared catalysts, i.e., surface area, pore volume, silver content, nano-sized silver crystals and their dispersion were measured using BET method, Atomic Absorption Spectroscopy, X-ray diffraction and TEM.

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Study of Cs-Promoted, α-Alumina-Supported Silver, Ethylene-Epoxidation Catalysts

Cited by 40 publications

References 19 publications

Surface Characterization Study of the Thermal Decomposition of Ag₂CO₃

Surface Characterization Study of the Thermal Decomposition of Ag₂CO₃

Ethylene Epoxidation in Low-Temperature AC Dielectric Barrier Discharge: Effects of Oxygen-to-Ethylene Feed Molar Ratio and Operating Parameters

Nano‐sized silver crystals and their dispersion over α‐alumina for ethylene epoxidation

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Study of Cs-Promoted, α-Alumina-Supported Silver, Ethylene-Epoxidation Catalysts

Cited by 40 publications

References 19 publications

Surface Characterization Study of the Thermal Decomposition of Ag2CO3

Surface Characterization Study of the Thermal Decomposition of Ag2CO3

Ethylene Epoxidation in Low-Temperature AC Dielectric Barrier Discharge: Effects of Oxygen-to-Ethylene Feed Molar Ratio and Operating Parameters

Nano‐sized silver crystals and their dispersion over α‐alumina for ethylene epoxidation

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Surface Characterization Study of the Thermal Decomposition of Ag₂CO₃

Surface Characterization Study of the Thermal Decomposition of Ag₂CO₃