Effect of strong metal-support interaction. II. Surface properties and catalytic activity of Ni/TiO/sub 2/ catalysts

X-ray photoelectron spectroscopy, electrical conductivity measurements, and H/sub 2/ and O/sub 2/ adsorption were used to study the surface properties of Ni/TiO/sub 2/ catalysts. The catalytic activities in the hydrogenation of CO and benzene were compared. The Ni/Ti ratio on the surface was found to decrease with increasing reduction temperature since the surface of the nickel crystals is shielded by titanium compounds: Ni/sub delta/Ti/sub 1-delta/O/sub 2/ phase at 350/degrees/C reduction temperature and the TiO/sub 2/ phase at 500/degrees/C. The partial shielding of the surface of the nickel crystals leads to a sharp difference in their size as determined by x-ray diffraction and chemisorption methods. An effect of the shielding of the nickel surface on the rate and selectivity of CO hydrogenation and the rate of benzene hydrogenation was not observed.