Effect of support and preparation on silver-based direct propylene epoxidation catalyst

Abstract

The effect of catalyst support and preparation method on silver-based catalysts for the direct vapor phase epoxidation of propylene to propylene oxide (PO) was studied. The shape of the CaCO 3 support is critical for optimum activity and selectivity of the catalyst. Among the CaCO 3 materials investigated as supports, the scalenohedral shape gives the best performance. A simplified method of catalyst preparation (referred to as ''slurry method'') was developed. With this method, it is not necessary to dissolve Ag 2 O into a solution as in the conventional incipient wetness method for preparing silver-based catalysts for propylene and ethylene epoxidation. The key to the slurry method is the addition of a small amount of an effective organic compound, such as ethanolamine, during the formation of the slurry.

Low-Temperature Selective Catalytic Reduction (SCR) of NOx with n-Octane Using Solvent-Free Mechanochemically Prepared Ag/Al2O3 Catalysts

“…More recently, highly loaded silver supported on calcium carbonate has been synthesized using ball-milling for propene epoxidation. 25 Although, in some cases, small amounts of solvent are used, ball-milling provides an opportunity for the synthesis step to be solvent-free, therefore circumventing many of the drying and precipitation steps normally involved in preparing such catalysts. Importantly, the technique has also been shown to produce materials that have different activities and selectivities compared with conventionally prepared catalysts.…”

“…The mechanochemically prepared material was inferior in the former reaction but superior in the second. More recently, highly loaded silver supported on calcium carbonate has been synthesized using ball-milling for propene epoxidation . Although, in some cases, small amounts of solvent are used, ball-milling provides an opportunity for the synthesis step to be solvent-free, therefore circumventing many of the drying and precipitation steps normally involved in preparing such catalysts.…”

Application of heterogeneous catalysts prepared by mechanochemical synthesis

“…The use of a mechanochemical ''slurry'' method for catalyst preparation has been described for the production of propylene oxide. 62 The catalysts were prepared by adding KNO 3 and Ag 2 O to deionized water followed by the addition of ethanolamine. The mixture was heated and, thereafter, the CaCO 3 support was added and the resulting mixture and ball milled.…”

Critical Role of Chlorinated Hydrocarbons in Propylene Epoxidation over K-Ag/CaCO3

“…Direct oxidation of C 3 H 6 to propylene oxide (PO) by O 2 environmentally and economically preferable to current industrial processes for synthesis of PO − achieves a maximal reported selectivity of only ∼50–60% over Ag/CaCO 3 catalysts in the presence of a variety of gas-phase and inorganic promoters including continuously co-fed trace alkyl chlorides (∼20–150 Pa C 2 H 5 Cl). − Alkyl chlorides, albeit in far lower partial pressure (e.g., ∼0.5-3 Pa C 2 H 5 Cl), are well-known gas-phase promoters for Ag-catalyzed epoxidation of other olefins by O 2 , most prominently ethylene and 1,3-butadieneeach achieving ≥90% epoxide selectivity over Ag/α-Al 2 O 3 in the presence of co-fed alkyl chlorides as well as inorganic promoters such as Cs, Mo, and Re. − Within ethylene epoxidation, these trace chlorinated hydrocarbons are known to slowly deposit Cl adatoms on Ag surfaces (denoted “Cl*”; eq ) which are also known to be removed under epoxidation conditions via oxychlorination (eq ) of trace, co-present hydrocarbons (e.g., ∼0.5 vol % C 2 H 6 ). ,− Dehydrochlorination : normalC x normalH y Cl + 0.25em * prefix+ normalO * prefix→ normalC x normalH y − 1 / normalO * prefix+ Cl * Oxychlorination : normalC x normalH y + normalO * prefix+ Cl * prefix→ normalC x normalH ...…”