PNNL

Abstract

Copper-exchanged metal–organic frameworks are active for selectively converting methane to methanol at 150 °C. We successfully synthesized mono- and dimeric Cu-oxo species at the node of MOF NU-1000 via a cation-exchange in different solvents. Combining studies of the stoichiometric activity, with characterization by in situ X-ray absorption spectroscopy, and density functional theory, we propose that hydroxylated dimeric Cu-oxo centers form after activation at 200 °C are responsible for the activity. The distance of the two Cu atoms is 2.87 Å and each Cu atom is coordinated by four O atoms with Cu-O distance of 1.95 Å in a distorted square planar configuration. Only approximately a third of the Cu centers is involved in converting methane to methanol. The authors gratefully acknowledge support for this work from the Inorganometallic Catalyst Design Center, an EFRC funded by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences (DE-SC0012702). This research used resources of the APS, which is a DOE Office of Science, Office of Basic Energy Sciences User Facility. Sector 20 operations at the APS are supported by the U.S. DOE (DE-AC02-06CH11357) and the Canadian Light Source. We thank Dr. Mahalingam Balasubramanian (APS X-ray Science Division) for assisting in the XAFS experiments. Most of the experiments were performed at Pacific Northwest National Laboratory (PNNL), a multi-program national laboratory operated by Battelle for the U.S. DOE. We also acknowledge the Minnesota Supercomputing Institute (MSI) at the University of Minnesota for providing resources that contributed to the research results reported within this paper.