(345d) Comparison Of Unpromoted Ferrochrome Wgs Catalysts To Those Promoted With Au Or Cu

A mechanistic kinetic study of the water-gas shift has been performed using a chromia promoted iron oxide catalyst. The kinetics have been found to be described quite well by either an oxidation-reduction (regenerative, redox) mechanism or by a formate mechanism. To complement the mechanistic kinetics, computational models of the surface intermediates have been generated using density functional theory. The same mechanistic models have also been studied using a copper-promoted ferrochrome catalyst. The addition of copper was found to lessen the severity of the kinetic inhibition by the product carbon dioxide. Computational models where copper was substituted at a lattice iron site were used to discriminate between the mechanistic models. Finally, a gold-promoted ferrochrome catalyst was studied kinetically. At higher temperatures the kinetics of water-gas shift were very similar to the kinetics of an unpromoted catalyst. At lower temperatures, however, it was found to be much more active than the unpromoted catalyst. The low temperature kinetics were studied and a consistent mechanistic model was formulated. The higher temperature results show that it is very difficult to discriminate between the two mechanistic models for water-gas shift on the basis of kinetics alone. The apparent reaction orders were observed to change significantly as the conditions changed. For the low temperature water-gas shift using a gold-promoted catalyst, the present study appears to be one of the first detailed investigations of the kinetics.