[Ag(μ‐en)][reo4]: an Intermediate During Preparation of the Ethylene Epoxidation Catalyst

Preparation of a catalyst for the ethylene oxide production requires impregnation of a porous corundum support with an aqueous silver ethylene diamine oxalate complex solution, to which among others NH4[ReO4] is added. Here we report on [Ag(mu-en)][ReO4] that precipitates from such a mixture. Single crystal structure analysis has revealed a striking similarity of the [Ag(mu-en)](+) entity with the same complex cation encountered in [Ag(mu-en)](2)(C2O4)x2H(2)O. Silver is coordinated end-on to the nitrogen atoms of the en ligands. The [ReO4](-) anions are not bonded to the silver cations, but instead involved in N-H center dot center dot center dot O hydrogen bonds to the ethylene diamine molecules. The first step of thermal degradation occurs at approximately the same temperature for both, the main component precipitate [Ag(mu-en)](2)(C2O4)x2H(2)O and [Ag(mu-en)][ReO4], warranting proximity of the rhenium promoter and the elemental silver deposit. At 300 degrees C, the temperature at which the catalyst for EO synthesis is commonly calcined, the decomposition product of plain [Ag(mu-en)][ReO4] under synthetic air is Ag[ReO4], in full analogy to industrial manufacturing process for selected Re-promoted EO catalyst formulations.