EFFECT OF REACTION MIXTURE, OXIDATIVE AND REDUCTIVE MEDIA ON ELEMENT DISTRIBUTION AND IRON VALENCE STATE ON THE SURFACE OF A MEDIUM-TEMPERATURE IRON-CHROMIUM CATALYST

XPS is employed for studying the effect of the reaction mixture (CO H-2), oxidative, and reductive media on the surface composition and ir on valence state on the surface of the medium-temperature iron-chromiu m catalyst for the water-gas shift reaction (STK-1-5). Two oxidation s tates of iron are revealed. In the first case, iron is bound with the chromia lattice, and, in the second case, iron exists in a free form a s a mixture of Fe(II) and Fe(III), preferably as Fe(III). Exposure to the reaction mixture with a low concentration of water vapor can lead to overreduction and carbonization of the catalyst. The effect of the reaction mixture at 450 degrees C results in the appearance of the iro n oxidation state similar to Fe3O4. This oxidation state appears to be the intermediate state between the iron oxidation states obtained aft er reduction at 450 and 250 degrees C. Activation of the reduced catal yst by oxidative treatment removes carbon deposits covering iron atoms .