Low‐field 2D NMR relaxometry to disclose the support-substrate interaction and surface dynamics in heterogeneous catalysis: A novel and complementary view to high field NMR relaxometry

Abstract

This work aims to disclose the support-substrate interaction and surface dynamics in heterogeneous catalysis by an original Low Field 2D NMR relaxation in complement to previous High Field NMR relaxometry. The combination of High Field NMR measurements with the new Low Field 2D NMR results presented in this work confirmed the possibility to extract information on local molecular dynamics and 2D surface dynamics for the complex system of aldehyde hydrogenation on Pd/C catalysts in the presence of a solvent. In particular, here multidimensional Low Field (2D) 1H nuclear magnetic relaxation experiments (T1-T2) have been used to characterize noninvasively the dynamical properties of benzaldehyde, octanal and p-xylene at surfaces of Pd-supported on carbon catalysts. 2D Low Field 1H NMR relaxation is sensitive to the environment of the reactant molecules and gives unambiguous information on the surface dynamics of the molecule; the association with previous 13C NMR relaxation at High Field s allows comparison between molecular orientations and local surface dynamics at surface of catalysts. In heterogeneous catalysis these new experimental and theoretical multiscale approaches link interfacial molecular dynamics and interaction with catalytic materials. This point is critical for disentangle chemical from physical reactant adsorption and deepening the role of the support material and its physical features in catalytic processes.