Session TOF. There are 5 abstracts in this session.

Session: MATERIALS 1, time: 4:00 - 4:25 pm

Metals, Linkers, and Guests: Three Targets for Solid-state NMR of Metal-organic Frameworks

Yining Huang
University of Western Ontario, London, Canada

Metal-organic frameworks (MOFs) have emerged and grown as the largest branch of porous materials. Although MOFs have numerous applications, the local structures, specific molecular-level features, and guest behaviors underpinning the unique properties and applications are often unknown. Solid-state NMR is a powerful tool for MOF characterization. Recently, we have examined many MOFs using a variety of NMR techniques. We have probed metal environment by interrogating 67Zn, 25Mg, 115In, 91Zr,71/69Ga, 129La, 39K, 43Ca, 47/49Ti via their SSNMR spectra; examined local structure around organic linkers by 1H,13C and 17O SSNMR; monitored the behavior of adsorbed gas molecules. We show combining information from three sources allows deeper understanding of the interplay between the structure of MOFs, their properties, and applications.

Session: MATERIALS 1, time: 4:25 - 4:50 pm

Solid-state NMR correlation analyses of heterogeneous catalysts

Brad Chmelka
UCSB, Santa Barbara, CA

Solid-state NMR, especially multidimensional techniques at low temperature, high field, or with DNP-enhancement, enable the properties of heterogeneous catalysts to be measured and understood in important new ways. Analyses of such materials have been limited by their non-stoichiometric compositions, heterogeneous surfaces, dilute species, or electrical conductivities, which result in complicated distributions of order and disorder that present severe sensitivity and resolution challenges. Nevertheless, J- and dipolar-mediated 2D 27Al{29Si}, 27Al{13C}, 13C{29Si},  and 15N{13C} NMR correlation analyses of zeolites and carbon electrocatalysts establish the local bonding environments and interactions at crucial heteroatom sites that are central to their macroscopic reaction properties. The results yield new insights on the atomic-level compositions and structures of industrially relevant catalysts for hydrocarbon conversion and electrochemical applications.

Session: MATERIALS 1, time: 4:50 - 5:15 pm

Zeolites Heterogeneous Catalysts Caught in the Act by (DNP) MAS NMR

Frédéric Blanc
University of Liverpool, Liverpool, United Kingdom

We will show how an approach combining 13C isotopic enrichment with multinuclear NMR and, on selected occasions, DNP MAS NMR, allows detection, structural identification and location of low concentration of carbocations formed during heterogeneous catalysis on a range of topologically different zeolites, enabling understanding of deactivation pathways. We also show that introducing hierarchical pores is a promising way to dramatically improve the overall DNP efficiency by a factor of ~ 4 on this type of materials.

Session: MATERIALS 1, time: 5:15 - 5:30 pm

Room Temperature Overhauser DNP of Lithium Dendrites: Selective Observation of the Solid–Electrolyte Interphase

Michael A. Hope1, 2; Bernardine L. D. Rinkel1; Anna B. Gunnarsdottir1; Katharina Marker1; Svetlana Menkin1; Clare P. Grey1
1University of Cambridge, Cambridge, UK; 2EPFL, Lausanne, Switzerland

Li metal anodes represent the ultimate energy density, but to address safety issues caused by dendrite formation, it is critical to understand the solid–electrolyte interphase (SEI) layer which forms on the metal surface. Dynamic nuclear polarisation (DNP) boosts sensitivity in NMR by harnessing the greater polarisation of unpaired electrons, however typical exogenous organic radicals are non-selective, could react with the SEI, and require cooling the sample to cryogenic temperatures. We instead exploit the inherent conduction electrons to hyperpolarise lithium metal at room temperature, utilising the Overhauser mechanism by which DNP was first discovered. This permits selective enhancement of the organic and inorganic SEI components, revealing their chemical nature and spatial distribution, via the 7Li, 1H and 19F NMR spectra.

Session: MATERIALS 1, time: 5:30 - 5:45 pm

Solid-State NMR of the Periodic Table with Fast MAS and Proton Detection

Amrit Venkatesh1, 2; Anuradha Wijesekara1, 2; Frédéric Perras2; Matthew Ryan1; Michael Hanrahan1, 2; Aaron Rossini1, 2
1Iowa State University, Ames, IA; 2Ames Laboratory, Ames, IA

In this contribution, we show that 1H detected, fast MAS methods can improve the sensitivity and resolution of solid-state NMR experiments with challenging isotopes in the periodic table. We demonstrate 1H detection of very low-γ spin-1/2 nuclei such as 89Y, 103Rh, 109Ag and 183W, and demonstrate LG-CP to suppress 1H spin-diffusion during cross-polarization. The D-RINEPT pulse sequence can be used to obtain HETCOR NMR spectra with half-integer quadrupolar nuclei such as 17O, 27Al, 35Cl, 71Ga and 91Zr. Improved HMQC pulse sequences that suppress t1-noise and allow arbitrary spectral widths are presented. We also report the use of frequency selective pulses to selective excite 1H signals and accelerate HMQC experiments with 14N and 17O.