Capping Ligands as Selectivity Switchers in Hydrogenation Reactions
Capping Ligands as Selectivity Switchers in Hydrogenation Reactions
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DOI：
10.1021/nl3027636
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发表时间：
2012-10-01
期刊：
影响因子：
10.8
通讯作者：
Shevchenko, Elena V.
中科院分区：
文献类型：
--
作者：
Kwon, Soon Gu;Krylova, Galyna;Shevchenko, Elena V.
本文系统地研究了纳米颗粒催化剂表面改性在炔烃加氢反应中的作用，并通过实验和计算方法对表面配体对Pt和Co/Pt纳米颗粒（NPs）催化剂选择性和活性的影响提出了一般性的解释。我们表明，适当的平衡之间的吸附能量的烯烃在表面的纳米粒子相比，封端配体定义的选择性的纳米催化剂的烯烃在炔烃加氢反应。我们报道了将伯烷基胺添加到Pt和CoPt 3 NP中可以将烯烃的选择性从0大幅提高到90%以上，转化率接近99.9%。增加NP表面上的伯烷基胺覆盖率导致辛烯的结合能降低，并且辛烯和伯烷基胺之间最终竞争吸附位点。在催化剂与伯烷基胺的足够高的覆盖度下，烷基胺获胜，这阻止了烯烃进一步氢化成烷烃。具有不同碳链长度的伯胺在催化剂表面具有相似的吸附能，因此对选择性具有相同的影响。当封端配体在催化剂表面的吸附能低于烯烃的吸附能时，封端配体不影响炔加氢制烯烃的选择性。另一方面，封端配体在催化剂表面的吸附能高于炔的吸附能，降低了其活性，导致炔的低转化率。
We systematically investigated the role of surface modification of nanoparticles catalyst in alkyne hydrogenation reactions and proposed the general explanation of effect of surface ligands on the selectivity and activity of Pt and Co/Pt nanoparticles (NPs) using experimental and computational approaches. We show that the proper balance between adsorption energetics of alkenes at the surface of NPs as compared to that of capping ligands defines the selectivity of the nanocatalyst for alkene in alkyne hydrogenation reaction. We report that addition of primary alkylamines to Pt and CoPt3 NPs can drastically increase selectivity for alkene from 0 to more than 90% with similar to 99.9% conversion. Increasing the primary alkylamine coverage on the NP surface leads to the decrease in the binding energy of octenes and eventual competition between octene and primary alkylamines for adsorption sites. At sufficiently high coverage of catalysts with primary alkylamine, the alkylamines win, which prevents further hydrogenation of alkenes into alkanes. Primary amines with different lengths of carbon chains have similar adsorption energies at the surface of catalysts and, consequently, the same effect on selectivity. When the adsorption energy of capping ligands at the catalytic surface is lower than adsorption energy of alkenes, the ligands do not affect the selectivity of hydrogenation of alkyne to alkene. On the other hand, capping ligands with adsorption energies at the catalytic surface higher than that of alkyne reduce its activity resulting in low conversion of alkynes.