Surface oxidation stale

EXAFS spectra for 1 wt.% Ni-loaded samples both before and after the reduction procedure, and also for Ni and NiO as standards, have also been examined [15], as shown in Figure 9. After reduction by H2 at 500 °C for 2 h, the loaded Ni was completely reduced to the metallic stale. Even after reoxidation by O2 at 200 °C for 1 h, most of the Ni remained metallic. (By XPS, the Ni, which remained on the external surface, was found to be in the oxidized form.) The formation of metallic nickel on a 0.1 wt.% Ni-loaded catalyst was also confirmed by ESR measurements... 

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