Investigation of the Origins of Selectivity in Ethylene Epoxidation on Promoted and Unpromoted Ag/α-Al2O3 Catalysts

Waugh, Kenneth C.; Hague, M.

doi:10.1016/b978-0-444-53188-9.00007-9

Cited by 4 publications

(1 citation statement)

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“…oxygen diffuses from the solid oxygen reservoir to the catalyst directly as suggested by Chan et al [6], noting that CeO2 does not release O2(g) at 270˚C. As CO2 was the only product of epoxidation on Ag-CeO2, the transport of oxygen from ceria to Ag must have favoured the creation of nucleophilic O-species, which are known to promote total combustion of C2H4 on silver [11,19].…”

Section: Discussionmentioning

confidence: 93%

High selectivity epoxidation of ethylene in chemical looping setup

Marek

Gabra

Dennis

et al. 2020

Applied Catalysis B: Environmental

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We describe the remarkable performance of a new catalyst for the chemical looping (CL-) epoxidation of ethylene, performed at atmospheric pressure and without any promoters added to either the catalyst or the feed gas. To undertake the CL-epoxidation of ethylene, silver was used as the catalyst, supported on either the perovskite SrFeO3 or Ce-modified SrFeO3. Here, the oxygen for the reaction is supplied to the silver catalyst from the active solid support, not from the gas stream. When the support has been reduced and depleted of oxygen, it is regenerated in a separate step with air, which makes the process cyclic and closes a chemical loop. Thus, there is no need to co-feed gaseous oxygen along with the ethylene feed, an important improvement in safety. Two methods were used to synthesise Ce-modified materials, employing either (i) the mechanical mixing of powdered CeO2 and the solid precursors of the perovskite, or (ii) the impregnation of a solution of cerium nitrate into solid particles of SrFeO3. In both cases, the materials were calcined to produce a mixture of CeO2 and SrFeO3. Both CeO2-SrFeO3 materials surpassed the unmodified SrFeO3 for CL-epoxidation. For the CeO2-SrFeO3 prepared by mechanical mixing, the production of ethylene oxide was stable over 15 cycles, giving 60% selectivity at 10% conversion of C2H4. In contrast, the material prepared by impregnation gave up to 85% selectivity but only in the first cycle of reduction, with the performance degrading over subsequent cycles. The reported results are better than the 50% selectivity achieved for the classical epoxidation using pure silver as the catalyst and feeds of gaseous ethylene and oxygen, without reaction promoters.

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Section: Discussionmentioning

confidence: 93%