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HREM analysis of the Nanostructure/Oxygen Buffering Capacity relationship in a Rh/CeTbO_x catalyst

机译:RH / CETBO_X催化剂中纳米结构/氧气缓冲能力关系的HREM分析

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A HREM investigation of the nanostructure of a 0.5% Rh/Ce_(0.8)Tb_(0.2)O_2 catalyst after a series of Oxygen Buffering Capacity (OBC) essays performed in the temperature range 473K- 773K has been carried out. The chemical changes suffered by the nanosized particles containing the noble metal, under the action of the pulsing 5% O_2/He atmosphere employed to run the OBC tests, have been monitored. Results indicate that in the experiments run at low temperature, 473K, rhodium is present in the catalyst as metallic nanoparticles. OBC experiments at 573K induce the transformation of the metal into an orthorrombic-Rh_2O_3 phase. In the HREM images obtained on the catalysts tested at the highest temperature, 773K, particles of both orthorrombic-Rh_2O_3 and tetragonal-RhO_2 have been detected. The stepwise increase in the oxidation state of rhodium revealed by the HREM study correlates quite well with the increase in the ability of the catalyst to damp down sudden changes in oxygen pressure. Further HREM results obtained from a sample coming out from an OBC experiment at 473K performed with a catalyst preoxidised at 773K suggest, nevertheless, that the bulk composition of the rhodium particles is not the unique factor to obtain high OBC values.
机译:0.5%的Rh / CE_的纳米结构的HREM调查(0.8)Tb_后(0.2)O_2催化剂一系列氧缓冲能力(OBC)的论文中所述的温度范围内473K- 773K已经进行执行。通过含有贵金属,用来运行测试OBC脉动5%O_2 / He气氛的作用下,纳米颗粒遭受的化学变化,已经被监测。结果表明,在实验中在低温下运行,473K,铑是存在于催化剂中作为金属纳米粒子。在573K OBC实验诱导的金属转变成一个orthorrombic-Rh_2O_3相。在上在最高温度下测试催化剂获得的HREM图像,773K,已经检测到两个orthorrombic-Rh_2O_3和正方晶RhO_2的颗粒。铑的氧化态的逐步增加揭示的高分辨电镜研究相关因素相当不错,在催化剂以抑制氧气压力的突然变化的能力增加。从在473K的OBC实验出来的样品得到进一步HREM结果与在773K预氧化建议,然而催化剂进行的,该铑粒子的主体组成是不获得高OBC值的唯一因素。

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