Effect Of Pretreatment Conditions On The Activity Of Gold Catalysts For CO Oxidation

Supported gold catalysts show unique low temperature activities in the CO oxidation reaction due to its excellent properties. Many factors affect catalytic activity, for example, support structure, the size of gold nanoparticles and the interaction between the gold species and the support. Catalyst pretreatment can change the interaction between the gold species and the support. In this paper, we studied the effect of different pretreatment conditions on catalytic activities of CO oxidation.Gold catalysts supported on CeO2 and Fe2O3 were prepared by deposition-precipitation method. CeO2 was prepared by hard template method, and Fe2O3 was prepared via hydrothermal method. Then the effect of preparation conditions and the atmosphere pretreatments of supported catalysts on CO oxidation were investigated.In the first part, CeO2 was prepared by hard template method, with hierarchical pore structure of monolithic silica as template. Au/CeO2 catalysts were prepared by deposition-precipitation method. The best vacuum drying time was 3 h. The catalytic activity was the best when Au/CeO2 was pretreated in reaction atomosphere at 250℃for 60 min. The morphologies of CeO2 support have significant effect on the catalytic activity of Au/CeO2, and the CeO2 support prepared by HMS was better than that prepared by KIT-6.In the second part, Au/CeO2 prepared by the best preparation conditions from the first part was pretreated in different atmosphere at 250℃. The results indicated catalytic activities of gold catalysts pretreated in different atomosphere were different. The order of CO oxidation activity was O2-H2≈O2>air≈H2-O2>H2≈unpretreated>N2.From the analysis of XRD, N2 adsorption and TEM, we found that there was little difference in structure and morphology. Besides, H2-TPR suggested that the relationship between Au and CeO2 is the main factor to catalytic activity.In the third part, the spindle and rhombohedrally shapes ofα-Fe2O3 nanoparticles were synthesized through hydrothermal method. And then two different shapes of Au/Fe2O3 catalysts were prepared by deposition-precipitation method. The two morphologies Au/Fe2O3 catalysts pretreated in different atmospheres exhibited different catalytic activities. The activity order of Au/Fe2O3 with spindle shape is:O2>N2>unpretreated>H2, and the order of 3 with diamond shape is:N2>O2>H2>unpretreated. For the spindle Au/Fe2O3 catalyst in O2 atmosphere, with different pretreatment temperatures, the activity order is:250℃>350℃>150℃.