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So far,it is still a controversial issue which status of gold species is a better active site for catalyzing CO oxidation.Herein,the influence of the different atmospheres pretreatment(oxidative and reductive)on gold state of Au/La-CeOx(1 wt％gold loading)catalyst during CO oxidation was studied.The changes of Au species were monitored by combined in situ diffuse reflectance infrared Fourier transform spec-troscopy(in situ DRIFTS)and X-ray photoelectron spectroscopy(XPS).For the sample pretreated with oxidative atmosphere,the data show that the initial Au3+is transformed to Auδ+(0 ＜ δ ＜ 1)during CO oxidation,which is a key step to lead to higher reactivity.For the sample after reductive atmosphere pretreatment,Auδ+is mixed with a small amount of Au0 which can be converted to Auδ+with the in-crease of temperature in reaction.Meanwhile,the sample always maintains high activity during the reaction.Therefore,the Auδ+obtained by reductive pretreatment is more active than the Au3+obtained by oxidative treatment in catalyzing CO oxidation.