Effect of water vapor and hydrogen treatments on the surface structure of Ni3Al foil

We have developed a water vapor treatment followed by hydrogen reduction to modify the surface structure of Ni3Al foils in order to obtain high catalytic activity. The Ni3Al foils were heat treated in water vapor at 873 K for 1 h followed by H2 reduction at 873 K for 1 h. The effects of the water vapor treatment and the H2 reduction on the surface structure of the Ni3Al foils were investigated by means of scanning electron microscopy and synchrotron radiation X-ray photoemission spectroscopy. Both Ni and Al in the surface layer of the Ni3Al foil were oxidized during the water vapor treatment; fine NiO particles with a high density were formed on the outermost surface, accompanied by the formation of oxide layers of Al(OH)3 and NiAl2O4/Al2O3 beneath the NiO particles. The NiO particles were reduced to metallic Ni and the Al(OH)3 was decomposed to Al2O3, whereas the NiAl2O4 and Al2O3 remained unchanged during the subsequent H2 reduction, forming a Ni-enriched porous structure on the surface layer of NiAl2O4/Al2O3.