Kinetics of temperature programmed reduction of Fe3O4 promoted with copper: application of iso-conversional methods

摘要

The temperature-programmed reduction of Cu/Fe3O4 in hydrogen was analyzed. The values of the apparent activation energy characteristic of this process were determined using the most widely known iso-conversional methods. In all cases a variation of the apparent activation energy with the degree of reduction was shown. The values of the pre-exponential factor were evaluated assuming various kinetic models. In all cases both the apparent activation energy and pre-exponential factor depend on the degree of reduction. Their values vary according to the relationship of the compensation effect: In A = a . E + b. The analysis of the data suggested that the reduction of Cu/Fe3O4 takes place passing through three consecutive stages, in which the reduction mechanisms are different. The existence of these reduction stages was tentatively explained taking into account the possible structural changes, which accompany the increase of the reduction degree. (C) 2003 Kluwer Academic Publishers. [References: 31]