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yingxingwang银虫 (小有名气)
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[求助]
这断英文须要高手帮忙啊
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Fig. 7 presents the H2-TPR profiles of the M-OMS-2 catalysts. Reduction of all the catalysts occurs in a temperature range of 170–350 °C. The peak position, area, and peak types vary among the catalysts (Table 1), indicating different influence of the doping metal on the OMS-2. These peaks between 200 °C and 350 °C can be ascribed to the hydrogen consumption during the formation of Mn2O3, the reduction of Mn2O3 to Mn3O4, and Mn3O4 to MnO [42]. From Fig. 7, one can readily observe that Cu-OMS-2 catalyst shows the highest reducibility with the largest H2 consumption (12.14 mol/g) and the lowest starting temperature of 170 °C, which might be caused by the reduction of Cu species [24]. Furthermore, the Fe-OMS-2 and Cr-OMS-2 catalysts show lower reducibility with the smallest H2 consumption (10.80 and 10.73 mol/g, respectively), and higher starting reduction temperature (272 °C and 275 °C, respectively). The reducibility of the M-OMS-2 catalysts decreases in the following ord er: Cu-OMS-2 > Ni-OMS-2 >Co-OMS-2 > Cr-OMS-2 > Fe-OMS-2. The higher reducibility indicates the higher mobility of the oxygen species in catalysts. Therefore, Cu can significantly improve the oxygen mobility in OMS-2 catalyst compared with the other doping metals. The TPR results correlate fairly well with the catalytic combustion activities and the XPS results. Similar results have been reported for the silver modified OMS-2 catalysts in the CO oxidation reaction[43]. Moreover, Hernández et al. [44] also suggested that Cu could improve the reducibility of OMS-2 and enhance the catalytic activity in preferential oxidation of CO. The promotion effect of Cu on the reducibility of OMS-2 could be attributed to the formation of Cu–O–Mn bridge and the hydrogen spillover from Cu atoms to manganese oxides [24,45]. Combined with the XPS and H2-TPR results, it can be concluded that the highest catalytic activity of Cu-OMS-2 catalyst can be ascribed to the richer defect-oxide species and the higher reducibility or oxygen mobility.Benzyl alcohol oxidation over OMS-2 catalyst has been proposed to obey the Mars–van-Krevelen (MVK) mechanism [31]. |
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8楼2013-04-07 17:09:44
hookhans
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2楼2013-04-05 15:39:00
yingxingwang
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