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The nature of active Ni sites and the role of Al species in the oligomerization of ethylene on mesoporous Ni-Al-MCM-41 catalysts
Applied Catalysis A: General ( IF 4.7 ) Pub Date : 2020-09-16 , DOI: 10.1016/j.apcata.2020.117831
Sara Moussa , Patricia Concepción , Maria A. Arribas , Agustín Martínez

Although nickel dispersed in mesoporous aluminosilicates are efficient catalysts for the oligomerization of ethylene, the nature of the active nickel sites still remains controversial. Here we applied in situ FTIR-CO spectroscopy during reaction with ethylene combined with reaction kinetics with online MS analysis of reaction products to unravel the nature of the active nickel species in working mesoporous Ni-Al-MCM-41 catalysts. The results revealed that isolated ion-exchanged Ni2+ cations are irreversibly blocked during the initial reaction stages leaving unsaturated Ni2+ cations grafted on silanols and at the surface of small (confined) NiO nanoparticles as the active species in the pseudo-steady state. The low activity of these species in pure silica materials suggested a promotional role of aluminum in the Al-MCM-41 matrix on enhancing the activity of Ni2+ sites, probably through a close interaction between Al species and nearby Ni2+ sites, as inferred from quantitative 27Al MAS NMR and FTIR spectroscopies.



中文翻译:

活性Ni位点的性质和Al物种在介孔Ni-Al-MCM-41催化剂上乙烯低聚中的作用

尽管分散在中孔铝硅酸盐中的镍是乙烯低聚的有效催化剂,但活性镍位的性质仍存在争议。在这里,我们在与乙烯反应过程中应用了原位FTIR-CO光谱,并结合了反应动力学和反应产物的在线MS分析,以揭示在工作介孔Ni-Al-MCM-41催化剂中活性镍物种的性质。结果表明,在初始反应阶段,分离出的离子交换的Ni 2+阳离子被不可逆地阻止,从而使不饱和Ni 2+阳离子接枝在硅烷醇上和小的(受限的)NiO纳米颗粒的表面上,成为拟态中的活性物种。-稳定状态。这些物质在纯二氧化硅材料中的低活性表明铝在Al-MCM-41基质中对增强Ni 2+活性具有促进作用,这可能是由于Al物种与附近的Ni 2+部位之间存在密切的相互作用,由定量的27 Al MAS NMR和FTIR光谱推断。

更新日期:2020-09-30
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