Carbon monoxide and propene oxidation by iron oxides for auto-emission control

Abstract

Activities of iron-based materials for the simultaneous total oxidation of CO and C 3H 6 were measured under conditions that were typical of automotive operation: space velocity of 35,000 h −1; temperatures between 373 and 873 K; atmospheric pressure; feed composition of 2.5% CO, 1.7% O 2, 0.5% H 2, 0.05% C 3H 6, and, optionally, 0.004% SO 2 in He. In the absence of SO 2, activity decreased in the order Fe 2 O 3 Al 2 O 3 > Fe 2 O 3 TiO 2 ~ Fe 2O 3 ⪢ FeSbO 4 > FePO 4 > Fe 2(MoO 4) 3 . CO and C 3H 6 removal followed apparent first-order kinetics and the data showed a compensation law effect. Oxidation was inhibited when SO 2 was present; temperatures for CO conversion over Fe 2O 3 were raised about 160 K, while the comparable rise for C 3H 6 oxidation was about 80 K. Inhibition was less with Fe 2O 3 on 35 m 2/g TiO 2 than with Fe 2O 3 on 350 m 2/g Al 2O 3 or with unsupported 5 m 2/g Fe 2O 3. Both FeSbO 4 and FePO 4 showed good activity for the conversion of C 3H 6, but not of CO, when SO 2 was absent. Material balances indicate that the partial oxidation product acrolein inhibits CO oxidation over these binary “selective oxidation” catalysts. Collectively, the data suggest that an inhibitor is created by oxidation of a precursor and its oxidation can be inhibited by the product of another feed component through control of the size of reactive ensembles on the catalyst surface.