Tuning the selectivity for ring-opening reactions of methylcyclopentane over Pt catalysts: A mechanistic study from first-principles calculations
Tuning the selectivity for ring-opening reactions of methylcyclopentane over Pt catalysts: A mechanistic study from first-principles calculations
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DOI：
10.1016/j.jcat.2011.09.021
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发表时间：
2012
影响因子：
7.3
通讯作者：
Zhi-Jian Zhao;L. Moskaleva;N. Rösch
中科院分区：
文献类型：
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作者：
Zhi-Jian Zhao;L. Moskaleva;N. Rösch
利用密度泛函方法，研究了甲基环戊烷转化为开环产物：支链己烷[2-甲基戊烷（2 MP），3-甲基戊烷（3 MP）]和非支链正己烷（nHx）的反应.我们分别用平坦的Pt（111）和台阶状的Pt（211）来描述富含台阶的大颗粒和富含缺陷的小颗粒。在Pt（111）上，所有通向支化己烷的基元步骤的势垒都低于90 kJmol −1，而nHx的形成在其C-C键断裂步骤中具有116 kJmol − 1的势垒。这一更高的势垒阻碍了nHx在Pt（111）上的形成，从而使实验观察合理化，即富含平台的大Pt颗粒选择性地产生支链己烷。然而，在Pt（211）上，形成nHx的C-C断裂势垒降低到94 kJmol −1，这意味着在缺陷上nHx的形成增强，与在富含缺陷的小Pt颗粒上观察到的基本统计产物分布一致。
Using density functional calculations, we studied the conversion of methylcyclopentane to its ring-opening products: branched hexanes [2-methylpentane (2MP), 3-methylpentane (3MP)], as well as unbranched n-hexane (nHx). We employed flat Pt(111) and stepped Pt(211) to describe terrace-rich large and defect-rich small Pt particles, respectively. On Pt(111), the barriers of all elementary steps for the paths leading to branched hexanes lie below 90kJmol−1, while the formation of nHx features a barrier of 116kJmol−1in its C–C bond scission step. This higher barrier impedes the formation of nHx on Pt(111) and thus rationalizes the experimental observations that terrace-rich large Pt particles selectively produce branched hexanes. However, on Pt(211), the barrier of C–C scission for the formation of nHx decreases to 94kJmol−1, thus implying enhanced formation of nHx over the defects, in agreement with the essentially statistical product distribution observed with defect-rich small Pt particles.