X-RAY ABSORPTION STUDIES OF THE NI ENVIRONMENT IN NI-MO-S

The local environment of the Ni atoms in the Ni-Mo-S phase has been elucidated by Ni K-edge EXAFS and XANES measurements of carbon-supported sulfided Ni-Mo catalysts. The results show that the Ni atoms have a low sulfur coordination number (less than six). This is contrary to recent reports in which an octahedral-like sulfur coordination have been suggested. It is proposed that the Ni atoms in Ni-Mo-S are located at the {Mathematical expression} edges of the MoS2 structure in square and tetragonal pyramidal type sites. These two types of sites can easily interconvert during sulfur addition/extraction and may as such be involved in the catalytic cycle. © 1990 J.C. Baltzer A.G. Scientific Publishing Company.