深入了解用于丙烷脱氢的 Ni/Al2O3 催化剂上选择性镍位点的性质,ACS Catalysis

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深入了解用于丙烷脱氢的 Ni/Al2O3 催化剂上选择性镍位点的性质
ACS Catalysis ( IF 11.3 ) Pub Date : 2022-10-03 , DOI: 10.1021/acscatal.2c03240
Rui Ma ₁ , Junxian Gao ₂ , Jiajing Kou ₃ , David P. Dean ₂ , Christian J. Breckner ₂ , Kaijun Liang ₁ , Bo Zhou ₁ , Jeffrey T. Miller ₂ , Guojun Zou ₁

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镍被认为是一种有前途的用于丙烷脱氢 (PDH) 的非贵金属，因为它具有激活烷烃分子的吸引人的能力；然而，选择性和稳定的镍位点的合成仍然是一个挑战。^{在此，我们通过将 Ni 2+}阳离子沉降到 γ-Al ₂ O _{3上的 Al}³⁺空位中来描述氧化铝支撑的孤立 Ni(II) 位点。作为PDH的选择性和稳定的Ni基催化剂。基于组合表征的结果，包括原位 X 射线吸附光谱 (XAS)、扫描透射电子显微镜 (STEM) 和原位漫反射红外傅里叶变换光谱 (DRIFTS)，原子分散的 Ni(II) 位点与证明了与来自氧化铝载体的氧离子的结合。PDH 催化剂测试表明，与负载型金属 Ni NP 催化剂相比，Ni(II) 单中心催化剂具有卓越的性能，在相当大的丙烷转化率 (15-45%) 下具有 > 93% 的丙烯选择性，超过了 Ni 纳米颗粒 (NP)催化剂。不同Ni结构对丙烯的选择性与结构表征的相关性表明，配位不饱和四面体Ni(II)位点促进了丙烯的解吸，从而抑制了焦化的副反应。此外，原子分散的 Ni(II) 位点在反应再生循环中保持在其局部结构中，原位 XAS 证明了这一点。这项关于氧化铝负载的镍催化剂的研究提供了对参与 PDH 反应的选择性和稳定镍位点的性质的见解。

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Insights into the Nature of Selective Nickel Sites on Ni/Al2O3 Catalysts for Propane Dehydrogenation

Nickel has been considered a promising nonprecious metal for propane dehydrogenation (PDH) because of its appealing ability to activate alkane molecules; however, synthesis of selective and stable Ni sites remains a challenge. Herein, we describe an alumina-supported isolated Ni(II) site by settling Ni²⁺ cations into Al³⁺ vacancy on γ-Al₂O₃ as a selective and stable Ni-based catalyst for PDH. Based on the results from combined characterizations, including in situ X-ray adsorption spectroscopy (XAS), scanning transmission electron microscopy (STEM), and in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS), atomically dispersed Ni(II) sites with bonding to oxygen ions from the alumina support are demonstrated. PDH catalyst tests shows that the Ni(II) single-site catalyst delivers superior performance compared to a supported metallic Ni NP catalyst, possessing >93% propylene selectivity at considerable propane conversions (15–45%), which surpasses Ni nanoparticle (NP) catalysts. The correlation of selectivity to propylene on different Ni structures with the structural characterizations suggest that the coordinatively unsaturated tetrahedral Ni(II) sites facilitate the desorption of propylene, which inhibits the side reactions for coking. Moreover, the atomically dispersed Ni(II) sites remain in its local structure in the reaction-regeneration cycles, as evidenced by in situ XAS. This study on alumina-supported nickel catalysts affords insights into the nature of selective and stable nickel sites involved in the PDH reaction.

更新日期：2022-10-03

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