烧绿石负载Ni用于甲烷重整制氢：探究不同A、B位离子替换的构效关系

发布时间：2018-04-10 03:33

本文选题：甲烷重整制氢　切入点：构效关系　出处：《南昌大学》2017年硕士论文

【摘要】：随着全球经济的飞速发展,煤碳和石油等化石能源消耗速度加快,但其储量有限,终将枯竭。此外,化石类燃料的不洁使用导致日益严重的环境污染,人类生存环境恶化。甲烷是天然气和页岩气的主要成分,相比煤碳和石油类石化能源更清洁,且来源丰富。甲烷重整是实现甲烷高值转化的主要途径之一,其中甲烷水蒸气重整制氢是目前工业用氢的主要来源,全世界约有1/2的氢气通过该方法制取。Ni基催化剂因其初始活性高且价格低廉,被广泛用于甲烷重整制氢。但目前工业上使用的Ni基催化剂在高温反应条件下易积碳、活性Ni物种易聚集并最终导致Ni基催化剂失活。因此,本论文在深入理解甲烷重整反应机理的基础上,从调变催化剂载体结构和控制Ni颗粒尺寸等角度出发,设计制备了含不同A位或B位离子的A_2B_2O_7烧绿石型复合氧化物载体,负载Ni用于甲烷重整制氢。主要内容和成果总结如下:第一部分:设计制备了B位为Zr离子但A位含不同稀土离子的Ln_2Zr_2O_7载体负载Ni用于甲烷水蒸气重整制氢。XRD和Raman结果表明,当A位离子依次为La~(3+),Pr~(3+),Sm~(3+)和Y~(3+)时,A、B位离子半径比r_(A3+)/r _(Zr4+)逐渐减小,Ln_2Zr_2O_7复合氧化物从严整的烧绿石结构(La_2Zr_2O_7),逐渐转变为无序的烧绿石结构(Pr_2Zr_2O_7和Sm_2Zr_2O_7),直至形成无序度很高的缺陷的萤石结构(Y_2Zr_2O_7),导致Ln_2Zr_2O_7结构中氧离子的无序性程度增大,流动性提高。H_2-TPR结果表明,活性组分Ni和无序性程度更大的Ln_2Zr_2O_7载体间的相互作用更强,从而导致Ni的分散度以及活性Ni物种的热稳定性更高。具有缺陷萤石结构的Y_2Zr_2O_7载体具有最多的活泼氧物种。因此,Ni/Y_2Zr_2O_7催化剂表现出了最高的反应活性、稳定性和抗积碳性能。第二部分:设计制备了A位为Y离子但B位含不同金属离子的Y_2B_2O_7载体负载Ni用于甲烷重整制氢。XRD和Raman结果表明,当B位离子依次为Ti~(4+)、Sn~(4+)、Zr~(4+)、Ce~(4+)时,A、B位离子半径比r_(Y3+)/r _(B4+)逐渐减小,Y_2B_2O_7复合氧化物从稳定的烧绿石结构(Y_2Ti_2O_7),逐渐转变为无序的烧绿石结构(Y_2Sn_2O_7),直至形成无序度很高的缺陷的萤石结构(Y_2Zr_2O_7和Y_2Ce_2O_7)。XPS结果表明,与Ni/Y_2Zr_2O_7和Ni/Y_2Ce_2O_7相比,Ni/Y_2Ti_2O_7和Ni/Y_2Sn_2O_7催化剂上具有更多的表面氧物种。H_2-TPR结果表明,与Ni/Y_2Zr_2O_7和Ni/Y_2Ce_2O_7催化剂相比,Ni或Ni_2Sn_3活性组分与Y_2Ti_2O_7和Y_2Sn_2O_7载体间具有明显更强的相互作用,从而将活性组分紧紧的锚定在载体表面并抑制其聚集,因此导致该两催化剂上活性金属比表面积更大、热稳定性更好。还原态Ni/Y_2Sn_2O_7催化剂上形成了Ni_3Sn_2物种,该物种显著提高了催化剂的抗积碳性能但明显牺牲了活性,因而限制了其工业应用前景。综上所述,Ni/Y_2Ti_2O_7催化剂表现出了最高的活性、稳定性和抗积碳性能。
[Abstract]:With the rapid development of the global economy, fossil energy consumption, such as coal and oil, has been accelerated, but its reserves are limited and will eventually dry up.In addition, the unclean use of fossil fuels leads to increasingly serious environmental pollution and deterioration of human living environment.Methane is a major component of natural gas and shale gas, cleaner and more abundant than coal and petroleum petrochemicals.Methane reforming is one of the main ways to realize the high value conversion of methane, in which steam reforming of methane is the main source of hydrogen for industrial use.About 1 / 2 of the hydrogen produced by this method is widely used in methane reforming for hydrogen production due to its high initial activity and low cost.However, at present, Ni based catalysts used in industry tend to deposit carbon at high temperature, and active Ni species tend to accumulate and lead to deactivation of Ni based catalysts.Therefore, on the basis of deep understanding of the mechanism of methane reforming reaction, from the point of view of adjusting the catalyst structure and controlling the size of Ni particles, the A_2B_2O_7 pyrochlore complex oxide carrier containing different A-site or B-site ions was designed and prepared.Supported Ni was used in methane reforming to produce hydrogen.The main contents and achievements are summarized as follows: in the first part, Ni supported on Ln_2Zr_2O_7 carrier with Zr ions at position B but different rare earth ions at site A has been designed and prepared for hydrogen production by steam reforming of methane. The results of XRD and Raman show that Ni carrier supported on Ni carrier is used in steam reforming of methane to produce hydrogen.The very high defect fluorite structure of Ys _ 2Zr _ 2O _ 7 leads to an increase in the degree of disorder of oxygen ions in the Ln_2Zr_2O_7 structure.The results of enhanced fluidity. H2-TPR show that the interaction between active component Ni and Ln_2Zr_2O_7 carrier with greater disordered degree is stronger, which leads to higher dispersion of Ni and higher thermal stability of active Ni species.Y_2Zr_2O_7 carriers with defective fluorite structure have the most active oxygen species.Therefore, the Ni / Y _ 2Zr _ 2O _ 7 catalyst exhibited the highest reaction activity, stability and resistance to carbon deposition.The second part: the Ni supported on Y_2B_2O_7 carrier with Y ion at position A but different metal ions in B site was designed and prepared for reforming methane to produce hydrogen. The results of XRD and Raman showed that Ni was used in reforming methane to produce hydrogen.The results of the trapped fluorite structure, Ys _ 2Zr _ 2O _ 7 and Y_2Ce_2O_7).XPS indicate that,Compared with Ni/Y_2Zr_2O_7 and Ni/Y_2Ce_2O_7, there are more surface oxygen species. H2-TPR results show that the active components of Ni or Ni_2Sn_3 have significantly stronger interaction with Y_2Ti_2O_7 and Y_2Sn_2O_7 supports than Ni/Y_2Zr_2O_7 and Ni/Y_2Ce_2O_7 catalysts.Thus, the active components were tightly anchored on the surface of the support and inhibited their aggregation, which led to the larger specific surface area and better thermal stability of the active metals on the two catalysts.A species of Ni_3Sn_2 was formed on the reduced Ni/Y_2Sn_2O_7 catalyst. The species significantly improved the carbon deposition resistance of the catalyst, but obviously sacrificed its activity, thus limiting its industrial application prospects.To sum up, the Ni / Y _ 2TiS _ 2O _ 7 catalyst showed the highest activity, stability and anti-carbon property.
【学位授予单位】：南昌大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ116.2

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