The effect of palladium clusters (Pd_n, n = 2-8) on mechanisms of acetylene hydrogenation: A DFT study

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• 作者：Jun-Nan Li ; Min Pu ; ^{pumin@mail.buct.edu.cn} ; Chi-Cheng Ma ; Ye Tian ; Jing He ; David G. Evans
• 关键词：Density functional theory ; Pdn clusters ; Acetylene hydrogenation ; Ethylene ; Mechanism
• 刊名：Journal of Molecular Catalysis A ; Chemical
• 出版年：2012
• 期刊代码：57_13811169
• 类别：ch
• 出版时间：July, 2012
• 卷：359
• 期：Complete
• 页码：14-20
• 文件大小：843 K

摘要

The mechanisms of acetylene hydrogenation on palladium clusters (Pd_n, n = 2-8) are researched by using the B3PW91/GENECP method of density functional theory. The calculation results indicate that there are two possible pathways for the hydrogenation reaction on Pd_n cluster from the reactant acetylene to the product ethane. One of the pathways undergoes through two intermediates, the vinyl (Pd_n(H)鈰疌HCH₂) and ethene (Pd_n鈰疌H₂CH₂) to form the ethane, and the other goes along vinylidene (Pd_n(2H)鈰疌CH₂), ethylidyne Pd_n(2H)鈰疌CH₃) and ethylidene (Pd_n(2H)鈰疌HCH₃) to ethane. Those intermediates in the two pathways can convert into each other which make the reaction profile complicated. The value of n in Pd_n cluster can directly affect the reaction pathway: when n 鈮?#xA0;4, the acetylene hydrogenation reaction will proceed via the pathway of Pd_n(2H)鈰疌HCH 鈫?/strong> Pd_n(H)鈰疌HCH₂ 鈫?/strong> Pd_n鈰疌H₂CH₂ 鈫?/strong> Pd_n(2H)鈰疌H₂CH₂ to form ethane. However, when n > 4, the reaction choose the following pathway: Pd_n(2H)鈰疌HCH 鈫?/strong> Pd_n(H)鈰疌HCH₂ 鈫?/strong> Pd_n鈰疌HCH₃ 鈫?/strong> Pd_n(2H)鈰疌HCH₃. In addition, the value of their turnover frequency (TOF) for the ethylene formation catalyzed by Pd_n cluster is larger than that for ethane, which indicates that the catalytic cycles in the formation of ethylene is efficient.