Surface is a matter having own chemistry, which provides unique material named “quasi-compounds”. Formation of active materials is essential on some catalysts. Formation of active hybrid layer composed of (-Rh-O-)/Pt on Pt-Rh(100) alloy, Pt/Rh(100), Rh/Pt(100), Rh/Pt(110), Pt/Rh(110) is a typical example, which is responsible material for superior active catalyst for NO reduction. Oxidation of CO is slow at 60^oC on a 1 wt. % Pt/TiO₂, but is very rapid on a Pt/TiO₂ covered with large amount of FeOx in the presence of H₂ and/or H₂O. In-situ IR spectroscopy proved a new catalytic oxidation (hydro-oxidation) of CO via HCOO and OH. Selective hydrogenation of DOM (CH₃OOCH₂-COOCH₃) on Au/SiO₂ influenced by small amount of Ag is a case of adsorption strength of intermediates influenced by additives.