The (1 x 1) Pt(100) surface is highly active for the reaction of NO and H-2, but the (1 x 2) reconstructed Pt(110) surface has almost no catalytic activity for this reaction even at 760 K. However, the deposition of a submonolayer of Ph atoms on the Pt(110) surface enhanced dramatically the activity for the NO + H-2 reaction, and the activity of the Rh/Pt(110) became as high as that of the p(3 x 1) Rh/Pt(100) surface. On the basis of the structure of the p(3 x 1) Rh/Pt(100) surface elucidated by STM, a common local structure of (Pt-RhO-Pt) layers was proposed for the Rh/Pt(110) surface.