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3.3 XPS results To discuss the oxidation state of Co species, the XPS spectra of Co 2p3/2 and Co 2p1/2 levels for Ag-containing catalysts are shown in Fig. 3a. It is known that the negative shifts of Co 2p3/2 peaks were due to the existence of higher oxidation state of Co4+ [9, 18]. The binding energy of Co 2p3/2 is only 779.3 eV even after the presence of some Co4+ ions in La1-xKxCoO3 perovskites. The binding energy of Co 2p3/2 is about 780.0 eV in present work, which is close to the binding energy of Co in LaCoO3 (779.7) and Co3+ in Co2O3 (779.6 eV)[13][ 20140619-44], Thus, Co species should exist as the low valence (Co2+ and Co3+) instead of Co4+. This result is in accordance to XRD and TPR results. Fig. 3b shows the XPS spectra of Ag species. For all samples, there are two main binding energy peaks corresponding to Ag 3d5/2 and Ag 3d3/2 levels at 368.2 eV and 374.2 eV with spin orbit separation of 6.0 eV. It has been reported that [14][ 20141011-15, [21] M. Kumar, G.B. Reddy, Phys Status Solidi B 246 (2009) 2232–2237.], Ag 3d5/2 peak at 368.2 eV indicates that Ag species exist as metallic Ag (Ag0) and Ag 3d5/2 peak , at 367.8 eV in the range 367.3–368.6 eV suggest Ag species exist as Ag+ and Ag2+, respectively. Therefore, Ag species in the surface of Ag/LaCoO3 is speculated to be mainly metallic state. The high symmetry of Ag 3d5/2 peak suggests the relatively homogeneous environment of Ag0. XPS spectra of O1s are demonstrated in Fig. 3c. For La1-XM1XCo1-YM2YO3 perovskites, it was suggested that the binding energy attributed to adsorbed oxygen in oxygen vacancy is 530.8 eV [9], that of chemisorbed oxygen and lattice oxygen are 532.7 eV [17], and 529.8 eV, respectively. [Co0.93La0.07 samples.] Ag/LaCoO3 displayed two peaks. The peak with a lower binding energy (528.6 eV) was assigned to lattice oxygen (Olat). The peak with higher binding energy (531.3-531.6 eV) was attributed to absorbed oxygen (Oads). The content of Oads species is as high as 67.7% on the surface of Ag/LaCoO3-400, which is much higher than that on the surface of Ag/LaCoO3-800 ( 56.6% ) and the data reported in previous works [ ]. This should be caused by the presence of more Ag0. 中括号内不译 |
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jiangguofeng
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络络依然: 金币+20, 翻译EPI+1, 感谢你的帮助 2015-03-30 10:45:54
络络依然: 金币+20, 翻译EPI+1, 感谢你的帮助 2015-03-30 10:45:54
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3.3 XPS测定结果 为了探讨钴物种的氧化态,用于含银催化剂水平的钴2p3／2和钴2p1／2的XPS光谱详见图3a。众所周知，钴2p3/2峰的负位移是由于Co4+[9,18]的高氧化态的存在。钴2p3/2的键能即使是在La1-xKxCoO3钙钛矿中出现一些Co4+离子之后也仅为779.3 eV。在本研究中钴2p3/2的键能约为780.0 eV,这接近于钴在LaCoO3 (779.7)中和Co3+在Co2O3 ( 779.6 eV)中的键能[13] [20140619 - 44]， 因此,钴物种应该以低价(Co2+和Co3+)而不是Co4+的形态存在。这一结论是依据XRD和TPR测定结果得出的。 图3b列出银物种的XPS光谱。对于全部样品,对应于银3d5/2和银3d3/2在368.2 eV和374.2 eV处有两个自旋轨道分离为6.0 eV的键能主峰。It h已有报道[14][20141011-15,[21] M.Kumar,G.B.Reddy, Phys Status Solidi B 246 (2009)2232-2237]说在368.2 eV处的银3d5/2峰表明以金属银(Ag0)形态存在的银物种和在367.8 eV处的银3d5/2（测程为367.3-368.6 eV）峰分别表示以Ag+和Ag2+形态存在的银物种。所以,据推测在银/LaCoO3表面的银物种为主要金属状态。银3d5/2峰的高对称性显示了Ag0的相对均匀环境。 O1s的XPS光谱显示于图3c。对于La1-XM1XCo1-YM2YO3钙钛矿,椐认为归因于氧缺位中吸附氧的键能为530.8 eV [9],化学吸附的氧和晶格氧的键能分别为532.7 eV [17]和529.8 eV。[ Co0.93La0.07样品]银/LaCoO3显示出两个峰。具有较低键能(528.6 eV)的峰归属于晶格氧(Olat)。具有较高键能(531.3-531.6 eV)可归属于吸附氧(Oads)。银/ LaCoO3 - 400表面上Oads物种的含量高达67.7%，这要比银/LaCoO3 - 800表面上的含量(56.6%)和以往的研究中的试验数据报告高很多。 这是由更多Ag0的存在所引起。 |
2楼2015-03-26 12:55:28