Studies of the methanation catalysts ThNi 5 and ZrNi 5 by Auger and Characteristic Energy Loss Spectra

Abstract

ThNi 5 and ZrNi 5 (fresh, used, and H 2S poisoned) have been examined by Auger spectroscopy (AES) and Characteristic Energy Loss Spectroscopy (CELS) to elucidate the strikingly different behavior of these materials as methanation catalysts. With use ZrNi 5 is transformed into Ni supported on ZrO 2 and ThNi 5 into Ni supported on ThO 2. AES indicates that the Ni on ZrO 2 is heavily overlaid with graphite. This does not occur with Ni and ThO 2, accounting for the exceptional activity of this catalyst compared to Ni on ZrO 2. Plasmon excitation energy determined from CELS are consistent with this picture. The large amount of surface Ni for the transformed ThNi 5 catalyst accounts for its high resistance to H 2S poisoning compared to that of ZrNi 5. A strong CELS peak is observed at 6.5 eV in ZrNi 5 and ThNi 5 as well as in elemental Ni, suggesting a very similar band structure for these materials. In this respect Ni and the Ni intermetallics are similar to Co and Co intermetallics as deduced from photoemission studies and recent APW band calculations.