Investigation of structural changes in the nickel–uranium oxide catalyst system by uranium L3-edge and nickel K-edge EXAFS and XANES

Abstract

The changes in local coordination about uranium and nickel that occur during the formation and treatment of a nickel–uranium oxide catalyst have been followed by EXAFS and XANES. Although the changes which are observed in the nickel K-edge EXAFS when the active catalyst is passivated or exposed to air are quite small, more significant changes are observed in the uranium L₃-edge EXAFS data when the samples are subjected to similar treatments. The uranium oxide lattice type, which is adopted at various stages of the preparation and treatment, has been determined by a qualitative comparison of the data with those recorded from uranium oxides. It is apparent that whilst the active and passivated catalysts have a uranium coordination similar to that of UO₂, exposure of the active catalyst to air causes a change in structure in which the uranium coordination environment resembles that of α-U₃O₈.