Site Densities, Rates, and Mechanism of Stable Ni/UiO-66 Ethylene Oligomerization Catalysts

Benjamin Yeh, Stephen P. Vicchio, Saumil Chheda, Jian Zheng, Julian Schmid, Laura Löbbert, Ricardo Bermejo-Deval, Oliver Y. Gutiérrez, Johannes A. Lercher, Connie C Lu, Matthew Neurock, Rachel B. Getman, Laura Gagliardi, Aditya Bhan

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Abstract

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-1 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.

Original languageEnglish (US)
Pages (from-to)20274-20280
Number of pages7
JournalJournal of the American Chemical Society
Volume143
Issue number48
DOIs
StatePublished - Dec 8 2021

Bibliographical note

Funding Information:
This work was supported by the Inorganometallic Catalyst Design Center, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES) (DE-SC0012702). Benjamin Yeh acknowledges the National Science Foundation for a graduate research fellowship and a departmental scholarship funded by 3M. The authors acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing computational resources. PXRD and STEM-EDS were carried out in the Characterization Facility, University of Minnesota, which receives partial support from the National Science Foundation (NSF) through the MRSEC program, with help from Xinyu Li and Rebecca Combs, respectively. Our research used resources of the Advanced Photon Source, a DOE-Office of Science user facility operated by Argonne National Laboratory and was supported by DOE under Contract No. DE-AC02-06CH11357 and the Canadian Light Source and its funding partners. Part of this work was also performed at Stanford Synchrotron Radiation Lightsource (SSRL) of SLAC National Accelerator Laboratory by Co-ACCESS, supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division. X-ray adsorption spectra were taken with the help of Dr. Mahalingam Balasubramanian and Dr. Adam Hoffman. We thank Dr. Brandon Foley, Dr. Jacob Miller, Dr. Matthew Simons, Zhichen Shi, and Neil Razdan for helpful technical discussions.

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© 2021 American Chemical Society.

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