Mossbauer Studies of Ferrous-A Zeolite: Part 2.—The Mobile Adsorption of Ethylene

Abstract

The titration of ethlene into dehydrated ferrous-A has been followed by 57Fe Mössbauer spectroscopy. The adsorption of ethylene increases the isomer shift and the quadrupole splitting of the single doublet of the outgassed sorbent. A 50% decrease in the Mössbauer absorption area is found when half the Fe2+ cations are covered with ethylene. Cooling the ferrous-A zeolite + adsorbed ethylene system to below 200 K caused the spectrum to split into two doublets. These changes show that the ethylene molecules are moving freely in the zeolite at room temperature but at temperatures below 200 K the molecules have residence times on the ferrous ion adsorption sites of the same order of magnitude as the half life of the Mössbauer event. Theoretical spectra have been derived to describe these experimental spectra based on such a hopping mechanism.