Mha. Elhamid et al., AUTOCATALYTIC REDUCTION OF HEMATITE WITH HYDROGEN UNDER CONDITIONS OFSURFACE CONTROL - A VACANCY-BASED MECHANISM, Journal of solid state chemistry, 123(2), 1996, pp. 249-254
An autocatalytic mechanism is shown to explain the kinetics of the sur
face reaction occurring during the low-temperature reduction of sinter
ed hematite pellets with hydrogen between 300 and 500 degrees C, The r
esults satisfactorily fit the predictions of a mechanism based on nond
issociative chemisorption of hydrogen on the oxygen vacancies at the s
urface of the hematite pellet. This chemisorption process activates th
e hydrogen molecule by substantially decreasing its bond energy and in
creasing its bond length, The calculated activation energy of the surf
ace reaction over this temperature range was found to be much smaller
than those reported earlier. The larger values are believed to have be
en affected by some diffusion control within the solid phase, as a res
ult of the limitations of the weight loss technique which was used in
those measurements. (C) 1996 Academic Press, Inc.