Ag-based electrocatalysts for ethylene epoxidation

Recent Developments in Heterogeneous Catalyzed Epoxidation of Ethylene to Ethylene Oxide

Epoxidation of ethylene to produce ethylene oxide (EO) is a vital heterogeneous catalytic chemical process in the industry, as EO is an important intermediate for the synthesis of fine chemicals including ethylene glycol, ethoxylates, plastics, and polyester. EO is commercially produced by the silver-catalyzed partial oxidation of ethylene with air or oxygen. However, it remains challenging to understand its chemical behavior under reaction conditions. To overcome this challenge, a series of catalysts with well-defined structures have been developed. The present review is devoted to summarizing the recent advances in the exploitation of novel catalytic materials for the epoxidation of ethylene, such as metal nanoparticles, clusters, single atoms, and bimetal. The role of promoters in selectivity enhancement will be discussed. A deep understanding of the active species, oxygen species, active structures, activity-structure relationship, and mechanisms contributing to the epoxidation process are highlighted. The integration with other advanced technologies such as electrocatalytic and photocatalytic is also reviewed. Finally, the current challenges and future prospects are provided so as to give guidance for the design of efficient catalysts for heterogeneous epoxidation of ethylene to EO, and to improve the fundamental understanding of the underlying catalytic chemistry.

Ag-Ce0.9Gd0.1O2-δ-Based Nanocomposite Thin Film Air Electrodes for Low-Temperature Solid Oxide Cells

Understanding and controlling the interfaces between different materials is crucial for developing solid oxide cells (SOCs) with both high performance and durability for low-temperature operation (<700 °C). Current research focuses on evaluating microstructural designs and composite material interactions to optimize SOC performance. Nanocomposite heterostructures exhibit unique properties at the interfaces, which are achieved through precise control of the composition, thickness, and surface chemistry. In this investigation, our goal was to develop nanocomposite films using a combination of a metal and a metal oxide. Specifically, we successfully fabricated Ag-Ce0.9Gd0.1O2-δ (Ag-CGO) nanocomposite thin films using pulsed laser deposition (PLD) in a single step. Dense Ag-CGO films with thicknesses of approximately 30 and 300 nm were grown on (100)-oriented yttria-stabilized zirconia (YSZ) substrates. The 300 nm-thick films exhibited an area-specific resistance (ASR) value of 22.6 Ω cm2 at 480 °C in a symmetrical cell configuration. This value is comparable to that of a micrometer scale-thick Ag electrode with a coarse porous microstructure. Therefore, Ag-CGO films represent a promising alternative to bulk Ag-based SOC electrodes by significantly reducing noble metal usage. The process described is suitable for integration into thin-film solid oxide fuel cell fabrication processes, as it eliminates the subsequent annealing step required to form a stable and active layer. Overall, this study provides valuable insights into enhancing the performance of metal/metal oxide thin films as SOC electrodes for low-temperature operation. While further investigations are necessary to optimize long-term stability, these films may also prove attractive for alternative catalytic applications operating at lower or ambient temperatures.

Electrochemical epoxidation enhanced by C2H4 activation and hydroxyl generation at the Ag/SnO2 interface

Direct electrochemical ethylene (C2H4) epoxidation with water (H2O) represents a promising approach for the production of value-added ethylene oxide (EO) in a sustainable way. However, the activity remains limited due to the sluggish activation of C2H4 and the stiff formation of *OH intermediate. This paper describes the design of a Ag/SnO2 electrocatalyst to achieve efficient electrochemical C2H4 epoxidation with a high faradaic efficiency of 39.4% for EO and a high selectivity of 91.5% at 25 mA/cm2 in a membrane electrode assembly. Results of in situ attenuated total reflection infrared spectra characterizations and computational calculations reveal that the Ag/SnO2 interface promotes C2H4 adsorption and activation to obtain *C2H4. Moreover, electrophilic *OH is generated on the catalyst surface through H2O dissociation, which further reacts with *C2H4 to facilitate the formation of *C2H4OH, contributing to the enhanced electrochemical epoxidation activity. This work would provide general guidance for designing catalysts for electrochemical olefin epoxidation through interface engineering.