THEORETICAL-STUDY OF HYDROGEN ACTIVATION IN A HEMATITE CLUSTER

The MINDO/SR method has been employed in order to study adsorption, dissociation and activation of hydrogen on a hydrodemetallation catalyst (hematite). A simple cluster model for hematite (Fe2O3) was utilized, and its calculated properties were compared with theoretical and experimental results. The effect of electronic density on the iron adsorption site was examined by changing the cluster charge ([Fe2O3]q, q = 0, -1). The results reveal that H2 is chemisorbed on an iron atom in a non-dissociative way, with a charge transfer from hydrogen to hematite. Ha interaction with oxygen atoms leads to deoxygenation and reduction of the hematite cluster. A negative charge on the cluster decreases H2 adsorption energy and the Fe-O bonds. A noticeable decrease in H-H diatomic energy with respect to the free H2 suggests that molecular hydrogen is activated on an iron atom site. © 1990.