Preparation Of Au/La-Mn-O Catalysts And Its Catalytic Activity For CO Oxidation

In this thesis, a series oxides La-Mn-O were prepared by sol - gel method and citric acid complex - hydrothermal method, and Au/La-Mn-O catalysts were prepared by deposition-precipitation (DP) method. The effects of the pH value,the calcination temperature,the gold loading and the kinds of carriers to the catalytic performance for CO low-temperature oxidation were studied in detail. Then the catalysts were characterized by means of XRD,BET,H2-TPR,XPS,TEM and FT-IR. To investigate the effect of support structure on the catalytic activity, the performance of catalysts derived from the oxides Mn₂O₃,the mixture oxides La2O₃+Mn₂O₃,the perovskite oxides La1-XSrXMnO₃ and the spinel oxides LiMn₂O₄ were compared.The catalytic activity results indicated that the support structure affected the catalytic performance. The catalyst derived from the perovskite oxides had better catalytic activity than that derived from other supports.Furthermore, the pH value,the gold loading and the calcination temperature also affected the catalytic activity. The catalyst obtained at pH of 9,the gold loading of 2% and without calcination showed high catalytic activity, especially the Au/La0.85Sr0.15MnO₃ catalyst, with T100 of 60oC.The stability experimental indicated that the catalysts calcined at 250℃had better stability than that of uncalcined catalyst. As the Au/LaMnO₃-S catalyst derived from the sol - gel method support was concerned, the T100 of uncalcined catalyst increased from 90℃to 100℃after 150-days preservation, while the calcined catalyst had the same activity with the fresh catalyst after 150-days preservation. Furthermore, the consecutive stability reaction testing revealed that the CO conversion can be maitained 100% over the Au/LaMnO₃-S catalyst during the stream of 30h.For the catalyst Au/LaMnO₃-CH from CH method support, T100 increased to 110℃from 100℃after 150-days preservation over the uncalcined catalyst, whereas same activity was found over the catalyst calcined at 250℃after 150-days preservation. The consecutive stability reaction testing revealed that the CO conversion can be maitained 100% over the Au/LaMnO₃-CH catalyst during the stream of 70h.Based on the characterization of XPS,FT-IR and TEM over the fresh and used catalyst, it was found that the oxidation state Au^δ+(0<δ<3) is the active species. Moreover, the aggregation of gold particles,the decrease of the oxidation state Au^δ+(0<δ<3),the decomposition of LaMnO₃ and the accumulation of carbonate probably resulted in the deactivation.