Abstract
The effects of cesium promoters on silver catalysts, supported by γ-alumina, were studied by adsorbing mono- or dilabeled [13C]ethylene onto the catalysts and performing low-temperature (70 K) solid-state13C NMR measurements on the ethylene. Selective isotopic enrichment was used to investigate the electronic environment present in and around the ethylene molecule as a function of promoter concentration. Changes in the spectroscopic parameters describing the ethylene lineshapes were extracted using a nonlinear least-squares procedure. These parameters were then used to determine the structure of the ethylene molecule on the surface and to probe the changes induced by adding cesium promoters. Similarly, the state of cesium in the catalyst system was investigated by spin-echo double-resonance spectroscopy and scanning electron microscopy X-ray fluorescence methods. The results imply that the form of cesium is not that of an oxide but, in all probability, reflect those of a cation–anion pair.
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