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Catalytic activation of ethylene C-H bonds on uniform d8 Ir(I) and Ni(II) cations in zeolites: toward molecular level understanding of ethylene polymerization on heterogeneous catalysts

preprint
revised on 04.10.2019 and posted on 04.10.2019 by Nicholas R. Jaegers, Konstantin Khivantsev, Libor Kovarik, Dan Klaus, Jian Zhi Hu, Yong Wang, János Szanyi

The homolytic activation of the strong C-H bonds in ethylene is demonstrated, for the first time, on d8 Ir(I) and Ni(II) single atoms in the cationic positions of zeolites H-FAU and H-BEA under ambient conditions. The oxidative addition of C2H4 to the metal center occurs with the formation of a d6 metal vinyl hydride, explaining the initiation of the Cossee-Arlman cycle on d8 M(I/II) sites in the absence of pre-existing M-H bonds. Under mild reaction conditions (80-220ᵒC, 1 bar), the catalytic dimerization to butenes and dehydrogenative coupling of ethylene to butadiene occurs over these catalysts. Butene-1 is not converted to butadiene under the reaction conditions applied. Post-reaction characterization of the two materials reveals that the active metal cations remain site-isolated whereas deactivation occurs due to the formation of carbonaceous deposits on the zeolites. Our findings have significant implications for the molecular level understanding of ethylene conversion and the development of new ways to functionalize C-H bonds under mild conditions.

Funding

The research described in paper is part of the Quickstarter Initiative at Pacific Northwest National Labor-atory. It was conducted under the Laboratory Directed Re-search and Development Program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Depart-ment of Energy. The research described in this paper was performed in the Environmental Molecular Sciences Laborato-ry (EMSL), a national scientific user facility sponsored by the DOE's Office of Biological and Environmental Research and located at the Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle.

History

Email Address of Submitting Author

Konstantin.Khivantsev@pnnl.gov

Institution

Pacific Northwest National Laboratory

Country

USA

ORCID For Submitting Author

0000-0002-4810-586X

Declaration of Conflict of Interest

No conflicts to declare

Version Notes

Version 2. The following changes have been implemented compared to Version 1: a). We have slightly modified the title to better emphasize the main message b). All the conclusions and graphs in the main text of the manuscript remain the same c). We have expanded the introduction section and discussion parts; we also added a few more references. d). Furthermore, we performed additional regular and isotopic spectroscopy experiments with deuterium, ethylene-d4, etc (summarized in Figs. S29-S33 supporting information) that further corroborate our findings.

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