Catalytic oxygen transfer between ethylene and ethylene oxide

Abstract

The transfer of oxygen between ethylene and ethylene oxide has been studied at surfaces of Ag, Au, (VO2)x, and bismuth molybdate. The study was carried out by following the rate of redistribution of isotopic carbon between ethylene and ethylene oxide. The conditions employed in the experiments were: temperature 22-305 [deg]C, partial pressure ratios of ethylene oxide to ethylene 0.1-50, contact time 1-10 sec. Silver was supported on high- and low-area Al2O3 zeolite and complexed with poly(4-vinyl-pyridine). Au was supported on Al2O3 and MgO. The dependence of the rate of isotopic redistribution upon the ratio of ethylene oxide to ethylene was taken as an indication of the process of reactive and competitive chemisorptions of ethylene and ethylene oxide. Information on the nature of the adsorption, in terms of number of surface centers per adsorbate molecule, was derived. From this point of view, the catalysts tested may be divided into two groups. In one group, single-center adsorption of ethylene predominated, while in the second the adsorption of ethylene included two surface centers per molecule. Thus, on the first group, ethylene fragmentation should not be favored. These catalysts, therefore, should prove more selective to ethylene oxide in the net reaction of ethylene oxidation with molecular O2. These predictions are fully confirmed by direct experimentation.