Kinetics of bismuth oxide reduction with propylene

Abstract

Propylene reacts directly with bismuth oxide to give C 6 olefinic products. A kinetic study was undertaken to elucidate the role of the bismuth oxide in this reaction. Experiments were carried out in a flow, microbalance reactor at atmospheric pressure, temperatures from 450 to 550 °C and propylene partial pressures of 0.1 – 1.0 atm, with N 2 as diluent. Bismuth oxide reduces to bismuth metal in propylene. After extensive reduction, the oxide cannot be completely regenerated due to the melting of the bismuth and consequent collapse of the structure. However, Bi 2O 3 supported on α-Al 2O 3 is regenerable. The rate of reduction increases with temperature and partial pressure of propylene. Analysis of the results strongly suggests that chemical reaction and bulk diffusion through the product layer are both important in defining the kinetics of the reaction. A model taking into account both processes is used to correlate the data. Since the diffusion rate diminishes with conversion faster than the chemical rate, the initial reduction of the catalyst is mainly limited by surface reaction whereas the continuing reduction is mostly diffusion controlled.