Patent Literature on Epoxidation of Propylene Over Silver Catalysts Using Molecular Oxygen – A Critical Industrial Review

Abstract

We summarize the patent literature related to the direct oxidation of propylene‐to‐propylene oxide (DOPO) over silver catalysts. Inventions claiming new compositions, preparation methods, and/or alternative process options are illustrated with data sampled from patent documents. Early claims focused on powders of silver (silver oxide) alloyed with and/or surface‐modified with one‐two promotors where silver was in large excess (>80wt%). In the following decades, inventors refined their approach and pursued alternative bulk synthetic methods supplemented with impregnation to formulations containing lower amounts of silver in combinations with various other transition metals, halides, alkalis and/or alkaline earth elements. Simultaneously, process development has facilitated increased PO selectivity via the co‐feeding of water and/or carbon dioxide at volume percent levels combined with smaller ppmV concentrations of organic chlorides and nitric oxides. At the end we briefly discuss how non‐catalytic oxidative routes to propylene oxide provide additional insights for new catalyst development. While these approaches hardly exceed 60% PO selectivity, they may shed light on design criteria for catalysts capable of achieving that goal. Success in the field will require strong fundamental understanding of the activation of dioxygen on catalytic surfaces to define design requirements for silver catalyst with high selectivity to PO via direct oxidation.

Internal 2D networking of silver bromide with a bidentate N-heterocyclic carbene ligand enables the formation of an inherently heterogeneous reusable catalyst for multicomponent A3 coupling

“…Silver catalysis has gained considerable attention in the past decade due to the low toxicity and cost-effectiveness of silver compared to other transition metals. Furthermore, it offers an attractive alternative in various catalytic applications, notably also in industrial processes such as the production of ethylene oxide 1 or formaldehyde. 2 In academic research, silver catalysts have been employed for fundamental construction of C–C bond, 3–5 as well as for forming C–N, 6–8 C–P, 9 C–F, 10,11 and C–B bonds.…”