XPS And Auger Studies of Selected Zr/Ni Intermetallic Alloy Catalysts

摘要

Various intermetallic alloys of Zr/Ni have been studied with regard to their surface compositions using Auger and XPS spectroscopies as a function of elevated temperature exposure to hydrogen and oxygen gas. ZrNi sub 5 , Zr sub 2 Ni sub 7 , ZrNi sub 3 , ZrNi and Zr sub 2 Ni, prepared by arc melting, were studied either as powders or as slices of the arc melted sample button. The elevated temperature treatments were chosen to duplicate the sample treatment these alloys received prior to catalytic hydrogenation. The alloys were sequentially analyzed with XPS and/or Auger techniques after the following representative treatment cycle: As-prepared; 400 deg C H sub 2 ; 400 deg C O sup 2 ; and a final 400 deg C H sub 2 exposure. In general, the as-prepared alloys are depleted in nickel at the surface (as compared to the bulk) and the alloys have been decomposed into a mixed Ni (or NiO) and ZrO sub 2 surface layer residing on the bulk alloy. After the elevated temperature H sub 2 treatment the NiO (if present) is reduced to Ni (>200 deg C) and additional ZrO sub 2 is formed. Elevated temperature O sub 2 treatment the NiO (if present) is reduced to Ni to segregate to the surface and form NiO (>200 deg C), which is reduced to Ni after the final 400 deg C H sub 2 treatment. After this general sequence of treatments, three alloys (ZrNi sub 5 , Zr sub 2 Ni sub 7 , and Zr sub 2 Ni) were found to have greater Ni surface concentrations than their corresponding bulk composition. These results follow the measured catalytic hydrogenation of ethylene to ethane activities which indicate that the higher the surface nickel concentration the greater the catalytic hydrogenation activity. (ERA citation 12:000735)