Nature of Active Nickel Sites and Initiation Mechanism for Ethylene Oligomerization on Heterogeneous Ni-beta Catalysts,ACS Catalysis

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Nature of Active Nickel Sites and Initiation Mechanism for Ethylene Oligomerization on Heterogeneous Ni-beta Catalysts
ACS Catalysis ( IF 11.3 ) Pub Date : 2018-03-30 00:00:00 , DOI: 10.1021/acscatal.7b03970
Sara Moussa ₁ , Patricia Concepción ₁ , María A. Arribas ₁ , Agustín Martínez ₁

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Higher olefins produced via ethylene oligomerization are versatile commodity chemicals serving a vast range of industries with large global economic impact. Nickel aluminosilicates are promising candidates to replace the homogeneous catalysts employed in industrial ethylene oligomerization processes. The current poor understanding of the true nature of the active nickel centers and the nickel-mediated oligomerization mechanism in these materials, however, hampers the rational design of improved catalysts. Here we applied in situ time- and temperature-resolved FTIR spectroscopy with simultaneous MS analysis of products to disentangle these fundamental issues using nanocrystalline Ni-beta zeolite as catalyst. We elucidate that isolated Ni²⁺ cations grafted on acidic silanols are the most likely active species in the working catalysts rather than the generally accepted ion-exchanged nickel cations. On the basis of our results, a plausible initiation mechanism involving a nickel vinyl hydride intermediate from which chain propagation proceeds similarly to the Cossee–Arlman pathway is proposed.

中文翻译：

活性镍位点的性质和多相Ni-β催化剂上乙烯低聚的引发机理

通过乙烯低聚反应生产的高级烯烃是通用的商品化学品，可服务于具有广泛全球经济影响的众多行业。铝硅酸镍有望取代工业乙烯低聚工艺中使用的均相催化剂。然而，目前对活性镍中心的真实性质以及这些材料中镍介导的低聚机理的了解不多，妨碍了改进催化剂的合理设计。在这里，我们应用原位时间和温度分辨FTIR光谱技术，同时对产品进行MS分析，以解决使用纳米晶Ni-β沸石作为催化剂的这些基本问题。我们阐明了孤立的Ni ²⁺接枝到酸性硅烷醇上的阳离子是工作催化剂中最可能的活性物种，而不是通常公认的离子交换镍阳离子。根据我们的研究结果，提出了一种合理的引发机制，其中涉及一种镍氢化乙烯中间体，其链增长与Cossee-Arlman途径相似地开始。

更新日期：2018-03-30

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