Rational design of highly effective catalysts based on the understanding of structure-activity relationship is becoming more and more important in heterogeneous catalysis. In this study, we have designed and successfully prepared a highly active PtFe nano-alloy catalysts with ultra-low Pt loading for the preferential oxidation of CO, over which CO can be completely removed at room temperature. As compared to the previously reported Pt@Fe quasi-core-shell catalysts with similar performance, the Pt loading of the as-prepared PtFe/Al2O3 nano-alloy catalysts can be decreased by a factor of 6 due to the increased Pt utilization. Based on in situ diffuse reflectance infrared spectroscopy (DRIFT'S) and quasi-in situ XPS, it can be concluded that O-2 is activated over ferrous iron on the PtFe/Al2O3 nano-alloy catalysts, leading to the high performance towards preferential oxidation of CO. Under reaction conditions, the active species will be oxidized to ferric oxide, thus O-2 activation ability and catalytic activity decrease. Based on the above understanding, we further constructed a highly stable catalyst by supporting PtFe nano-alloy particles onto TiO2, which can help to activate O-2 and stabilize the lower valence Fe species. (C) 2015 Elsevier B.V. All rights reserved.