Yeh Benjamin, Vicchio Stephen P, Chheda Saumil, Zheng Jian, Schmid Julian, Löbbert Laura, Bermejo-Deval Ricardo, Gutiérrez Oliver Y, Lercher Johannes A, Lu Connie C, Neurock Matthew, Getman Rachel B, Gagliardi Laura, Bhan Aditya
Department of Chemical Engineering and Materials Science, University of Minnesota-Twin Cities, 421 Washington Avenue SE, Minneapolis, Minnesota 55455, United States.
Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina 29634-0909, United States.
J Am Chem Soc. 2021 Dec 8;143(48):20274-20280. doi: 10.1021/jacs.1c09320. Epub 2021 Nov 24.
Nickel-functionalized UiO-66 metal organic frameworks (MOFs) oligomerize ethylene in the absence of cocatalysts or initiators after undergoing ethylene-pressure-dependent transients and maintain stable oligomerization rates for >15 days on stream. Higher ethylene pressures shorten induction periods and engender more active sites for ethylene oligomerization; these sites exhibit invariant selectivity-conversion characteristics to justify that only one type of catalytic center is relevant for oligomerization. The number of active sites is estimated using in situ NO titration to disambiguate the effect of increased reaction rates upon exposure to increasing ethylene pressures. After accounting for augmented site densities with increasing ethylene pressures, ethylene oligomerization is first order in ethylene pressure from 100 to 1800 kPa with an activation energy of 81 kJ mol at temperatures from 443-503 K on Ni/UiO-66. A representative Ni/UiO-66 cluster model that mimics high ethylene pressure process conditions is validated with ab initio thermodynamic analysis, and the Cossee-Arlman mechanism is posited based on comparisons between experimental and computed activation enthalpies from density functional theory calculations on these cluster models of Ni/UiO-66. The insights gained from experiment and theory help rationalize evolution in structure and stability for ethylene oligomerization Ni/UiO-66 MOF catalysts.
镍功能化的UiO-66金属有机框架材料（MOFs）在经历与乙烯压力相关的瞬态过程后，在没有助催化剂或引发剂的情况下使乙烯齐聚，并在连续运行超过15天的时间里保持稳定的齐聚速率。较高的乙烯压力缩短了诱导期，并产生了更多用于乙烯齐聚的活性位点；这些位点表现出不变的选择性-转化率特征，这表明只有一种类型的催化中心与齐聚反应相关。使用原位NO滴定法估计活性位点的数量，以消除乙烯压力增加对反应速率增加的影响。在考虑到随着乙烯压力增加位点密度增大之后，在443-503K的温度下，在Ni/UiO-66上，乙烯压力从100至1800kPa时，乙烯齐聚反应对乙烯压力呈一级反应，活化能为81kJ/mol。通过从头算热力学分析验证了一个模拟高乙烯压力工艺条件的代表性Ni/UiO-66簇模型，并基于对这些Ni/UiO-66簇模型进行密度泛函理论计算得到的实验和计算活化焓之间的比较，提出了Cossee-Arlman机理。从实验和理论中获得的见解有助于阐明乙烯齐聚Ni/UiO-66 MOF催化剂的结构和稳定性演变。
