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在过去的25年,纳米金催化剂上CO氧化反应得到广泛研究,但始终没有一致的结论.这是因为影响纳米金催化活性的因素很多,包括金的价态、载体的性质、氧空位、金属与载体之间的相互作用等,尤其是各影响因素之间相互牵制,增加了催化反应机理的研究难度.氧化铈载体表面氧缺陷的浓度较高,有利于活性金属组分在其表面的稳定和分散,因此氧化铈纳米晶负载的Au催化剂受到广泛关注.此外,当CeO_2晶格中部分Ce被化学性质不同的其它元素取代后,可以促进CeO_2晶格氧的活化,提高氧的储放能力,从而有利于催化反应进行.因此,本文采用水热法合成了组成均匀的CeO_2,CeZrO_x和CeZrLaO_x三个载体,并通过沉淀-沉积法负载金.利用X射线衍射(XRD)、拉曼光谱(Raman)、X射线光电子能谱(XPS)、高分辨透射电镜(HRTEM)、X射线吸收精细结构(XAFS)和氢气程序升温还原(H_2-TPR)等技术分析了催化剂的物相结构、表面性质、形貌以及金纳米颗粒的大小和价态等性质,并结合其在CO氧化反应中催化性能的差异,探讨影响金催化剂活性的关键因素.XRD,TEM,HRTEM和XAFS结果表明,三个载体上所得金纳米颗粒的平均尺寸都在2–4nm,且分散较好;XPS结果表明,影响催化剂活性的关键因素不是金的价态,而是载体表面的活性氧物种.从Raman结果可知,掺杂后的氧化铈载体上氧空位浓度明显增加,因而催化剂活性都有所提高.H_2-TPR进一步探讨了三个载体以及负载金后其氧化还原能力的变化,结果表明,金和载体之间的相互作用可以增强载体的氧化还原性能以及表面氧空位浓度,进一步提高了催化剂活性,而负载金催化剂氧化还原性能的变化与载体的组成密切相关.由于锆的掺杂可使金与载体之间相互作用减弱,而镧则增强了二者间相互作用,因此Au/CeZrLaO_x催化剂上锆和镧的协同掺杂作用使其表面活性氧物种浓度最高,低温时表现出最高的催化活性.
In the past 25 years, the oxidation of CO on gold nanoparticles has been extensively studied, but there is no consistent conclusion, because there are many factors affecting the catalytic activity of gold nanoparticles, including the valence of gold, the nature of the support, the oxygen vacancy, the metal And the interaction between carriers and so on, especially the mutual restraint between the various factors, increasing the difficulty of the catalytic reaction mechanism research.Corrosive carrier surface oxygen defect concentration is higher, is conducive to the stability of the active metal component on its surface And dispersed, so cerium oxide nanocrystals supported by the Au catalyst has received widespread attention.In addition, when CeO 2 lattice part of the Ce by other elements of different chemical properties, can promote the activation of CeO 2 lattice oxygen and improve oxygen storage capacity So as to facilitate the catalytic reaction.Therefore, three hydrothermally synthesized CeO_2, CeZrO_x and CeZrLaO_x carriers were prepared by hydrothermal method, and supported by precipitation-deposition method.The XRD and Raman spectra of (Raman), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), X-ray absorption fine structure (XAFS) and hydrogen temperature programmed reduction (H 2 -TPR) XRD, TEM and HRTEM were used to investigate the phase structure, surface properties, surface morphology, size and valence of Au NPs, and their catalytic performance in CO oxidation. And XAFS results showed that the average size of the gold nanoparticles obtained on the three carriers are in the range of 2-4nm and the dispersion is better. The XPS results show that the key factor affecting the activity of the catalyst is not the gold valence but the active oxygen Species.According to the results of Raman, the oxygen vacancy concentration on the doped ceria carrier significantly increased, and the activity of the catalyst was increased.H_2-TPR further explored the changes of the redox capacity of the three carriers and the gold The results show that the interaction between gold and support enhances the redox properties of the support and the surface oxygen vacancy concentration and further enhances the activity of the catalyst.The change of the redox properties of the supported gold catalyst is closely related to the composition of the support.Due to the doping of zirconium The interaction between gold and support can be weakened, while lanthanum enhances the interaction between the two. Therefore, the synergistic doping of zirconium and lanthanum on Au / CeZrLaO_x catalyst With the highest concentration of surface active oxygen species, showing the highest catalytic activity at low temperatures.