Abstract
Supported Ag catalysts on silica and corundum have been synthesized applying an improved impregnation technique. The resulting Ag particle sizes can be divided into three categories concerning: (I) bulk-like, (II) nanoparticles of 1–6 nm, and (III) in situ created Ag clusters below 1 nm. Ag nanoparticles and bulk-like Ag are investigated concerning their pretreatment dependence for CO oxidation showing that harsher pretreatment conditions need to be applied for smaller particle sizes, based on their tendency to form Ag2CO3. A particle size effect for Ag in oxidation reactions is investigated using CO oxidation as a test reaction. The CO oxidation performance is increasing with decreasing particle size with Ag clusters showing the highest activity. A novel method based on the adsorption of ethylene (C2H4) as sensor molecule is further used to discriminate the silver–oxygen (Ag–O) interaction strength of bulk-like Ag, Ag nanoparticles, and Ag clusters, showing a distinct Ag–O chemistry for the three individ...
Highlights
Supported Ag catalysts are used in several oxidation reactions such as of carbon monoxide[1] and methanol[2] or epoxidation of ethylene[3] and propene.[4]
All samples were thoroughly analyzed by multiple techniques including powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA) coupled to evolved gas analysis (EGA), inductive coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy with energy dispersive X-ray detection (SEM/EDX), and transmission electron microscopy (TEM)
Benefits are the use of low vacuum (60 mbar), rotation of the flask, and controlled addition of impregnation solution, all occurring in a closed system
Summary
Supported Ag catalysts are used in several oxidation reactions such as of carbon monoxide[1] and methanol[2] or epoxidation of ethylene[3] and propene.[4]. The unique character of Ag compared to other metals is reasoned in the activation of oxygen on the surface and subsurface, while stable oxide phases at elevated temperatures and atmospheric pressure[26] are absent This intriguing surface and subsurface silver−oxygen (Ag−O) chemistry explains why, for example, for the ethylene epoxidation reaction exclusively supported Ag catalysts are used. The present work deals for the first time with the investigation of the Ag−O chemistry for a series of silica supported Ag catalysts with solely Ag nanoparticles of
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