ACTIVE SITES ON MAGNETITE WATER-GAS SHIFT CATALYSTS.

Magnetite, Fe//3O//4, is commercially used as a high temperature water-gas shift (WGS) catalyst. The mechanisms proposed for this reaction generally fall into two categories: regenerative and associative. The regenerative class of mechanisms view the catalyst as an intermediary oxygen transfer agent which interacts with the two reactants, CO and H//2O. The associative class of mechanisms treats the reaction in a Hougen-Watson fashion wherein the two reactants interact directly on the catalytic surface. The nature of the active site in the reaction has received less attention than the reaction mechanism and is considered in this paper. A method of titration of active sites for WGS is developed using the chemisorption of CO and CO//2. It is shown that the interaction with the support also causes a perturbation of the effective charge of the octahedral iron cations, and this is believed to be responsible for the observed change in the catalytic activity. NO chemisorption is apparently insensitive to the effective cation charge, but CO//2 and CO are not.