A colloidal crystal template method coupled with a precursor complexion process was developed to create three-dimensionally ordered macroporous (3 DOM) Au/CeO2 catalyst. The resultant Au/CeO2 catalyst possesses well-defined 3DOM structure, and shows enhanced catalytic performance for formaldehyde (HCHO) oxidation with 100% HCHO conversion at similar to 75 degrees C. The catalytic mechanism of HCHO catalytic oxidation over 300MAu/CeO2 catalyst was systematically investigated by means of gas chromatograph (GC), H-2-temperature programmed reduction (H-2-TPR), temperature programmed surface reaction (TPSR), CO2-temperature programmed desorption (TPD), and Fourier transform infra-red (FT-IR) spectroscopy. GC results indicate that HCOOH intermediate is generated during HCHO catalytic oxidation. TPD and TPSR tests show that the weak absorption ability of CO2 over 3 DOM Au/CeO2 catalyst and the existence of Au active species in ionic and metallic states in 3 DOM Au/CeO2 catalyst largely improve the catalytic activity, favoring the enhanced HCHO catalytic oxidation. FT-IR tests prove that the carbonate and hydrocarbonate formed on the surface of 3DOM Au/CeO2 catalyst during HCHO catalytic oxidation may account for its deactivation. Based on the above investigation, a new catalytic mechanism of enhanced HCHO catalytic oxidation over 300M Au/CeO2 catalyst is proposed. The mechanism may afford the scientific guidance for preparing high efficiency oxide supported noble metal catalysts and present a solution for solving their deactivation problem. (C) 2011 Elsevier B.V. All rights reserved.