The oxidation of ethylene over silver-based alloy catalysts 4. Silver-zinc alloys

Toreis, N

doi:10.1016/0021-9517(88)90192-3

Cited by 10 publications

(8 citation statements)

References 34 publications

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“…% in the bulk (corresponding to 85% Cd on the surface) . In the case of Ag–Zn catalysts the segregation of Zn to the surface is so strong, that the concentration of Zn on the surface reaches more than 80% already for catalyst with 1 at % Zn in bulk and remains almost unchanged with further increase of nominal Zn content leading to constant selectivity values ( S = 67%) for all investigated Ag–Zn catalysts …”

Section: Introductionmentioning

confidence: 89%

“…The supported Ag–Cd and Ag–Zn catalysts were investigated under ethylene epoxidation conditions within relatively wide concentration ranges with up to 35 at % Cd and 20 at % Zn. , The surfaces of these catalysts are strongly enriched in Cd or Zn even before their exposure to ethylene epoxidation conditions, and under reaction conditions the formation of oxides is even more pronounced. The selectivity toward EO using supported Ag–Cd catalysts increases up to 82% with increasing Cd content reaching a maximum at 35 at.…”

Section: Introductionmentioning

confidence: 99%

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Anisotropic Reactivity of CaAg under Ethylene Epoxidation Conditions

et al. 2018

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The chemical behavior of CaAg as catalyst for ethylene epoxidation was studied using a combination of experimental (X-ray powder diffraction, scanning electron microscopy, thermal analysis and infrared spectroscopy), and quantum chemical techniques as well as real-space chemical bonding analysis. Under oxidative ethylene epoxidation conditions, the CaAg (010) surface possesses an outstanding stability during long-term experiments. It is caused by the formation of an ordered, stable and dense CaO passivation layer with a small amount of embedded Ag atoms. On this way, the (010) surface constitutes a kinetic barrier for further incorporation of oxygen into the subsurface region and thereby prevents further oxidative decomposition of CaAg. The calculated adsorption energies of the reaction species show strong adsorption of the reaction products that may explain the observed low conversion of ethylene toward ethylene oxide using CaAg as catalyst.

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Section: Introductionmentioning

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Anisotropic Reactivity of CaAg under Ethylene Epoxidation Conditions

et al. 2018

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“…In case of the doped or alloyed Ag catalysts, e.g. the Ag-Cu, Ag-Cd, Ag-Pd, Ag-Zn systems, the picture becomes even more complicated because of possible segregation of one of the components to the surface and/or bulk transformation of the material [9,[14][15][16][17]. The induction phase for almost all Ca-Ag compounds can be identified by monitoring the selectivity towards ethylene oxide.…”

Section: Duration Of the Induction Phasementioning

confidence: 99%

“…The complexity of the material increases from the single crystal of elemental Ag through polycrystalline materials towards supported and highly promoted industrially used Ag/α-Al 2 O 3 catalysts. Insertion of a second element either in the form of doping (e.g., Cu [9,[12][13][14], Pd [15]) or alloys (Zn [16], Cd [17], Au [18]) leads to the preferential segregation to the surface and formation of oxidic phases due to the different reactivity of the components and random distribution of the elements in the crystal structure. Contrary to alloys, in (ordered) intermetallic compounds (IMCs) the atoms (preferentially) occupy certain crystallographic positions and chemical interactions can be properly described in terms of local chemical bonding.…”

Section: Introductionmentioning

confidence: 99%

Ca–Ag compounds in ethylene epoxidation reaction

Antonyshyn

Sichevych

Ormeci

et al. 2019

Science and Technology of Advanced Materials

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The ethylene epoxidation is a challenging catalytic process, and development of active and selective catalyst requires profound understanding of its chemical behaviour under reaction conditions. The systematic study on intermetallic compounds in the Ca-Ag system under ethylene epoxidation conditions clearly shows that the character of the oxidation processes on the surface originates from the atomic interactions in the pristine compound. The Ag-rich compounds Ca 2 Ag 7 and CaAg 2 undergo oxidation towards fcc Ag and a complex Ca-based support, whereas equiatomic CaAg and the Ca-rich compounds Ca 5 Ag 3 and Ca 3 Ag in bulk remain stable under harsh ethylene epoxidation conditions. For the latter presence of water vapour in the gas stream leads to noticeable corrosion. Combining the experimental results with the chemical bonding analysis and first-principles calculations, the relationships among the chemical nature of the compounds, their reactivity and catalytic performance towards epoxidation of ethylene are investigated.

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“…Scanning electron microscopy studies of the Cu−Ag catalyst showed that the Ag morphology remained unchanged, but enrichment of Cu was found by X-ray photoelectron spectroscopy (XPS) on the surface of the catalyst, indicating that a high degree of dispersion of Cu on the silver particles had been achieved. Verykios and co-workers have studied several promoted systems and reported results for Zn, Au, , Pd, and Cd additives. Zn was found to have little effect on the Ag catalysts, while Cd was found to increase the turnover frequencies of both the combustion and epoxidation reactions .…”

Section: Introductionmentioning

confidence: 99%

Promoter-Induced Morphological Changes of Ag Catalysts for Ethylene Epoxidation

Dellamorte

Lauterbach

Barteau

2009

Ind. Eng. Chem. Res.

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The combination of high-throughput reactor experiments and scanning electron microscopy analysis of promoted Ag catalysts provides critical insights into mechanistic and morphological changes. In particular, catalysts promoted with Cu, Cd, Au, Pt, and Re were analyzed to understand the morphological effects of these promoters on the Ag particles. Cu increases the sintering of Ag particles, while Cd and Re were found to alter the Ag particle sizes into a trimodal distribution. However, contrasting effects of Re and Cd were found on the catalyst activity. Cd-Ag catalysts exhibited a 5-fold increase in the ethylene conversion for a variety of Cd loadings, compared to unpromoted Ag. Moderate increases in conversion and selectivity were seen with the addition of 25 ppm Re, while further Re impregnation led to decreases in ethylene conversion and ethylene oxide selectivity. Au and Pt block surface Ag sites by nucleating as separate particles on the silver surface. In doing so, they reduce the activity of the catalyst, but also reduce the sintering of the Ag particles.

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The oxidation of ethylene over silver-based alloy catalysts 4. Silver-zinc alloys

Cited by 10 publications

References 34 publications

Anisotropic Reactivity of CaAg under Ethylene Epoxidation Conditions

Anisotropic Reactivity of CaAg under Ethylene Epoxidation Conditions

Ca–Ag compounds in ethylene epoxidation reaction

Promoter-Induced Morphological Changes of Ag Catalysts for Ethylene Epoxidation

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