Oxidation treatment of carbon aerogels supports to modulate Ru/CA catalysts for Fischer-Tropsch synthesis
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摘要: 氧化处理炭材料已被证明是用于开发高效和稳定负载催化剂的有效方法。用不同的氧化剂(H2O2和HNO3)对碳气凝胶(CA)的表面进行了功能化处理。在功能化、未功能化的CA载体上采用浸渍法制备了一系列的Ru基催化剂。利用XRD、Raman光谱、N2物理吸附-脱附、H2-TPR、FT-IR和XPS系统地研究了氧化处理对碳气凝胶的织构特征、形成的表面含氧官能团的类型和含量、金属与载体的相互作用以及对催化剂费托反应性能的影响。实验结果表明,未功能化的催化剂显示出最高的初始活性和糟糕的稳定性。相比之下,Ru/CA-H2O2催化剂表现出优异的活性和C5+的选择性。表征结果表明,氧化处理增加了碳气凝胶的缺陷,从而增大了比表面积。载体表面含氧官能团含量的提高增强了载体和Ru纳米颗粒之间的相互作用,提高了催化剂的稳定性。然而,表面上过多的含氧官能团降低了碳气凝胶负载的Ru催化剂的活性和C5+选择性。Abstract: Oxidation treated carbon materials for exploiting highly efficient and stable loaded catalysts have been proven to be valid. In this work, the surfaces of carbon aerogels (CA) were functionalized with different oxidizing agents, i.e., H2O2 and HNO3. A series of Ru-supported catalysts on carbon aerogels (CA) with/without functionalized were prepared by the impregnation strategy. The impact of oxidation treatment on the texture features of carbon aerogels, the types and contents of formed surface oxygen-containing functional groups, the metal-support interactions and the Fischer-Tropsch synthesis reaction performances of the catalysts were systematically investigated. Our results showed that Ru/CA catalyst without oxidation treatment displayed the highest initial activity but the poor stability, while the Ru/CA-H2O2 catalyst exhibited excellent activity and C5+ selectivity. The oxidation treatment increased the carbon aerogels defects, thereby broadening the specific surface area. The increased content of oxygen-containing functional groups on the surface enhanced the interaction between the support and Ru nanoparticles and improved the stability of the catalyst. Nevertheless, the excessive oxygen-containing functional groups on the surface decreased the activity and the C5+ selectivity of carbon aerogels-loaded Ru catalysts.
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Table 1 Ratio of I(D) to I(G) of the CA-X supports from Raman spectra
Sample I(D)/I(G) Ru/CA 2.61 Ru/CA-H2O2 2.90 Ru/CA-HNO3 2.72 Table 2 Textural properties and Ru elemental analysis of the Ru/CA-X catalysts
Sample SBETa/(m2·g−1) vporeb/(cm3·g−1) Dporec/nm Ru mass percentage w/% Ru/CA 531.42 1.27 22.28 4.24 Ru/CA-H2O2 594.27 1.36 19.95 4.76 Ru/CA-HNO3 592.41 1.31 20.43 4.17 a: BET surface area, b: cumulative volume of pores by BJH desorption, c: average pore diameter calculated by 4 × vpore/SBET, d: mass fraction of Ru was measured by ICP Table 3 Concentrations of surface oxygen groups of the Ru/CA-X catalysts
Atom type Peak position/eV Group Percentage/% Ru/CA Ru/CA-H2O2 Ru/CA-HNO3 C 1s 284.8 C−C 62.35 52.88 49.13 286.0 C−O 8.90 13.85 12.78 287.3 C=O 11.73 10.66 9.83 288.8 −COOH 8.77 9.19 14.71 291.5 π−π* 8.26 7.53 4.59 O 1s 531.4 C=O 30.45 29.50 21.87 532.5 −OH 30.22 34.87 41.16 533.4 −O− 28.97 24.73 22.37 534.8 −COOH 7.80 8.44 12.60 536.4 H2O 2.57 2.47 2.00 O/C ratio − − 0.36 0.50 0.52 -
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