High-Resolution NMR of the Hydrogenation Reaction with Parahydrogen in an Inhomogeneous Magnetic Field

Nuclear magnetic resonance is extremely attractive for operando studies of chemical reactors. However, the heterogeneous catalyst particles placed inside an NMR probe greatly affect the uniformity of the magnetic field. This problem is especially acute when studying heterogeneous hydrogenation processes using parahydrogen. Despite the increased sensitivity due to hyperpolarization, under conditions of a strong heterogeneity of the magnetic field, the antiphase nature of the NMR signals leads to a partial or even a complete loss of spectroscopic information due to significant NMR signal broadening. The use of intramolecular multiple-quantum coherences in 2D NMR allows one to circumvent this problem. We used the COSY pulse sequence to acquire 2D NMR spectra of the reaction mixture upon propene hydrogenation with parahydrogen. The selection of double-quantum coherences in the resulting 2D NMR spectrum allowed us to obtain a highly resolved NMR spectrum under conditions of severe inhomogeneity of the magnetic field caused by the presence of catalyst granules.