The original surface of a solid is not always active as a catalyst, but the surface becomes active during reaction. Activation of surfaces may be classified as follows; (i) originally active surfaces, (ii) intermediates produced by reaction with surface atoms, (iii) formation of active sites with functional groups, (iv) formation of active surface compounds, (v) cooperation of multiple catalytic processes. In this review, we discuss two important environmental reactions, one is NO + H-2 -> 1/2 N-2 + H2O catalyzed by single crystal Pt-Rh-ally and Pt/Rh or Rh/Pt bimetals, and the other is the preferential oxidation (PROX) reaction of CO in H-2 by heavily FeO(x) under bar-loaded Pt/TiO2 catalyst and Pt-supported carbon with Ni-MgO. The specific activity of the Pt-Rh catalyst arises from the formation of special ordered bimetallic surface layers composed of (-Rh-O-) on Pt-layer. Formation of an active over-layer compound was confirmed on Pt0.25Rh0.75(100) alloy, Pt/Rh(100), Rh/Pt(100), Pt/Rh(110) and Rh/Pt(110) bimetal surfaces. The PROX reaction of CO in H-2 was attained on two new catalysts, one being FeOx/Pt/TiO2 (ca. 100 wt.% FeOx) and the other Pt supported on carbon with Ni-MgO. The mechanism of the PROX reaction of CO was deduced by in situ DRIFT spectroscopy, which indicates a coupled reaction of CO + OH- -> HCOO- and HCOO + OH -> CO2 + H2O. (C) 2012 Elsevier B. V. All rights reserved.