XAS and XRD Studies on the Structural Changes of NiRaney Catalyst after a Hydrogenation Process

Ni-Raney catalysts have a sponge-like structure and are largely applied in reactions of organic hydrogenation. The industrial production has the advantages of low cost and simple process, however this catalyst has the inconvenient of the easy deactivation. The understanding of the deactivation mechanism has motivated several studies, some of them identifying a surface restructuration and loss of the active sites. In this work, we present XRD and XAS measurements at the Ni K edge of Ni-Raney samples obtained before and after an industrial reaction of olefin hydrogenation. We show that in the deactivation process, the porous structure of Ni grains becomes closer to the massive structure, presenting a higher number of first neighbors and an increase of the crystalline coherence. These results call into question the usual hypothesis of collapse of the porous structure.