Catalytic oxygen transfer between propylene and propylene oxide

Abstract

The transfer of oxygen between propylene and propylene oxide has been studied at surfaces of silver, gold and (VO2)x. The study was carried out by following the rate of isotopic carbon distribution between propylene and propylene oxide. The following conditions were employed in the experiments: temperature, 60 to 270 [deg]C; partial pressure ratio propylene oxide to propylene, 0.35 to 30; contact time, 1 to 10 sec. No homogeneous reaction nor catalytic decompositions were detected. CO2 formation was 2O3 or complexed with poly(4-vinylpyridine); gold was supported on MgO. The influence of the ratio of the partial pressures of propylene oxide to propylene on the reaction rate was quantitatively measured on each catalyst and taken as an indication of processes of competitive reactive chemisorption of propylene and propylene oxide. The analysis showed that on silver supported on low area Al2O3, single site adsorption was predominant, while two site adsorption prevailed at the surfaces of the other catalysts tested. Some amount of mixed behavior occurred on all catalysts. Kinetically, the carbon isotope exchange reaction was analyzed in terms of sequence of adsorption-desorption steps. By combining the rate of these steps with that of similar steps for ethylene and ethylene oxide it was possible to predict conditions for the epoxidation of propylene by means of ethylene oxide. A semiquantitative confirmation of this prediction gave supporting evidence for the internal consistence of the kinetic model discussed.