Preparation Of Nano-sized Gold Catalyst Au/La-Fe-O And Their Catalytic Performance For CO Oxidation

Supported gold catalysts are a new kind of catalytic materials and exhibite fine catalystic activity for variety reactions, including oxidation of low temperature of carbon monoxide and volatile organic compounds, water-gas shift and some other selective oxidation reaction. So the research on gold catalyst has been the focus due to the fine application potentials of industrial and environmental protection. In recent years, more attentions have been paid to the new methods for the preparation of the gold catalysts with low gold loadings and high activity, especially the high stability.In this paper, a series oxides La-Fe-O were prepared by sol-gel method and the catalysts were prepared by deposition-precipitation(DP) method. The effects of the pH value,the gold loading,the calcination temperature and the supports to the catalytic performance for CO oxidation were investigated. Then these catalysts were characterized by means of XRD,BET,AAS,H2-TPR and FT-IR. The performance of catalysts derived from the oxides Fe2O3,the mixiture oxides La2O3+Fe2O3 and the perovskite oxides LaFeO3 were compared for CO oxidation. In order to improve the catalyst stability, Fe(OH)3 was added as well.The experiment results indicate that:(1) the support structure and the kind of support affected the catalytic performance. The catalysts derived from oxides Fe2O3 and the perovskite oxide LaFeO3 had batter catalytic activity than that derived from other supports. (2) The preparation condition had influence on the catalyst activity. The catalyst Au/LaFeO3 obtained at pH value of 7,the gold loading of 2% and the uncalcined catalysts exhibited high catalytic activity. CO was totally converted to CO2 at the temperature of 0℃. (3) The stability experimental indicated that the catalyst Au/LaFeO3 calcined at 100℃had better stability than that of uncalcined catalyst. The 170-days preserved catalysts revealed nearly same activity with the fresh catalysts, but the T100 of uncalcined catalyst increased from 0℃to 60℃. Furthermore, the stability of fresh catalysts was superior to that of 170-days preserved catalysts. Au/Fe(OH)3/LaFeO3 and Fe(OH)3/Au/LaFeO3 had better stability than Au/LaFeO3.Based on the characterization of XPS and FT-IR over the fresh and calcined catalyst, it was found that that oxidation state Auδ+(0<δ≤3) is the active species. The decrease of oxidation state Auδ+(0<δ≤3),the accumulation of carbonate on the catalyst surface and the growth of the crystallite size of gold may be main reasons for deactivation of the catalyst.