AUTOCATALYTIC REDUCTION OF HEMATITE WITH HYDROGEN UNDER CONDITIONS OF SURFACE CONTROL - A VACANCY-BASED MECHANISM

摘要

An autocatalytic mechanism is shown to explain the kinetics of the surface reaction occurring during the low-temperature reduction of sintered hematite pellets with hydrogen between 300 and 500 degrees C, The results satisfactorily fit the predictions of a mechanism based on nondissociative chemisorption of hydrogen on the oxygen vacancies at the surface of the hematite pellet. This chemisorption process activates the hydrogen molecule by substantially decreasing its bond energy and increasing its bond length, The calculated activation energy of the surface reaction over this temperature range was found to be much smaller than those reported earlier. The larger values are believed to have been affected by some diffusion control within the solid phase, as a result of the limitations of the weight loss technique which was used in those measurements. (C) 1996 Academic Press, Inc. [References: 44]