Overview of Selective Oxidation of Ethylene to Ethylene Oxide by Ag Catalysts

Abstract

Ethylene oxidation by Ag catalysts has been extensively investigated over the past few decades, but many key fundamental issues about this important catalytic system are still unresolved. This overview of the selective oxidation of ethylene to ethylene oxide by Ag catalysts critically examines the experimental and theoretical literature of this complex catalytic system: (i) the surface chemistry of silver catalysts (single crystal, powder/foil, and supported Ag/α-Al2O3), (ii) the role of promoters, (iii) the reaction kinetics, (iv) the reaction mechanism, (v) density functional theory (DFT), and (vi) microkinetic modeling. Only in the past few years have the modern catalysis research tools of in situ/operando spectroscopy and DFT calculations been applied to begin establishing fundamental structure–activity/selectivity relationships. This overview of the ethylene oxidation reaction by Ag catalysts covers what is known and what issues still need to be determined to advance the rational design of this important catalytic system.

The Lord of the Chemical Rings: Catalytic Synthesis of Important Industrial Epoxide Compounds

“…The aforementioned reaction is commonly made in fixed bed reactors using Ag/Al2O3 as catalyst operating at 230-270 °C and at a pressure of 1-3 MPa [20,21]. To the best of our knowledge, there are no reviews concerning the synthesis of oxirane in gas, liquid, and liquid-liquid reaction systems.…”

“…The aforementioned reaction is commonly made in fixed bed reactors using Ag/Al 2 O 3 as catalyst operating at 230-270 • C and at a pressure of 1-3 MPa [20,21].…”

“…In Figure 2, the ethylene oxidation reaction is reported. One of the interesting aspects indicating the performance of a catalyst in this type of reaction is the selectivity [20]. It was shown that there is a correlation between selectivity itself and the conversion; in particular the selectivity decreases with the increase of the conversion [23].…”

“…In particular, in the presence of unpromoted silver catalyst the selectivity towards ethylene oxide is approximately 50% while using promotors it can reach a value higher than 90% [20,25]. For this reason, the promotors are used in industrial applications, in fact the industrial catalyst is constituted by Ag particles supported on alumina with alkali compounds as promotors [22].…”

Directing transition metal-based oxygen-functionalization catalysis

“…Note that the carbonyl group coordinated to ruthenium may function as an axial ligand to enhance triplet excited lifetime, which is conducive to photoinduced electron- Thus, pure Ag metal catalyst can only obtain EO selectivity up to 40-50%. 87,88 The addition of alkali metals like Cs and Re or atomic Cl as additives or inhibitors, to Ag catalyst was found to increase the epoxidation selectivity up to 80%. 89 The selectivity Reproduced with permission.…”