Parahydrogen Signal Enhancement within a Magic Angle Spinning Rotor: Proof-of-Principle of a New Operando NMR Methodology for Studies of Heterogeneous Catalysis
EMSL Project ID
49957
Abstract
Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectroscopy is a powerful method for the elucidation of structure and dynamics on the atomic-length scale. Yet, NMR has had relatively limited in the field of heterogeneous catalysis. Two reasons for this are (1) engineering of an MAS system for high temperatures and pressures and (2) the inherently low sensitivity of the technique. The first issue has been solved by the development of a high-pressure MAS NMR system at PNNL. The sensitivity problem is addressed in this proposal, where the focus is on hydrogenation catalysis. Parahydrogen induced polarization (PHIP) is a hyperpolarization methodology that can amplify high-field NMR signals by up to 5 orders of magnitude. The metastable proton singlet spin order of parahydrogen (p-H2), invisible to NMR, is transformed into NMR-observable hyperpolarization via symmetry breaking chemistry. At the University of Florida (UF), PHIP by heterogeneous catalysis (het-PHIP) is performed using a continuous-flow gas/solid hydrogenation reactor located adjacent to the NMR magnet. The gaseous reaction products flow into the superconducting magnet for sensitivity-enhanced NMR detection. While this approach has proven effective in studies of a variety of catalysts, it does not provide direct access to intermediates, adsorbates, or time-resolved kinetics, as would in-situ/operando spectroscopy. Proof-of-principle studies aim to demonstrate the feasibility of observing PHIP NMR signals within the volume of a sealed MAS sample rotor. The initial focus is hydrogenation of simple alkenes and alkynes over supported Pt and silica-encapsulated Pt-Sn intermetallic nanoparticles (INPs). If successful, MAS-PHIP NMR will open the door to a plethora of catalytic materials and reactions.
Project Details
Project type
Limited Scope
Start Date
2017-07-03
End Date
2017-09-02
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members