NMR Study of Species Formed during Ethylene Oxidation over Supported Silver

Article abstract of DOI:10.1021/j100085a033

¹³C solid-state NMR spectroscopy has been used to study the various species formed during the oxidation of ethylene on Ag catalysts.The NMR spectra obtained after heat treatments of sealed catalyst samples provide direct observation of surface species which can be identified by their chemical shift values.This study also reports ¹³C shifts for standard compounds dispersed on Ag/η-Al2O3 and Ag/SiO2 which provide groups that can be present under reaction conditions, and the decomposition of ¹³C-labeled ethylene oxide on Ag/SiO2 in the absence of O2 was investigated.On the basis of these experiments, ¹³C assignments have been made for the following absorbed species: ethylene oxide, formic acid, formate, oxalic acid, oxalate, acetic anhydride, acetaldehyde, and carbonate.In the absence of O2, ethylene oxide decomposed to acetic acid, acetaldehyde, and formaldehyde, and broad peaks indicative of polymers on the SiO2 surface were also observed.The observation of ethylene oxide adsorbed on Ag/SiO2 after reaction between ¹³C2H4 and O2 was consistent with a previous study showing this catalyst was much more selective than a Ag/η-Al2O3 catalyst; CO2, adsorbed ¹³C2H4, and a deprotonated oxalate or formate species were also identified.The formation of CO2 in the absence of aldehyde or acetate species but in the presence of oxalate species suggests an alternative route may exist for complete oxidation that does involve isomerization of ethylene oxide.