Spectroscopic characterisation of molecules adsorbed at zeolite surfaces

Abstract

The present review focuses mainly on the interaction between molecules and the surfaces of zeolites and opens with Electron Spin Resonance (ESR) spectroscopy in view of the desire to study radical intermediates in catalytic systems. In this aim too, the family of spectroscopic techniques known collectively as μSR (Muon Spin Rotation, Relaxation or Resonance) which employ spin-polarised positive muons, and can probe radicals in porous media, including zeolites, with a unique and remarkable sensitivity are paid due attention. All such methods have undergone appreciable developments in recent years, especially in regard to pulsed-techniques and theoretical methods for data acquisition and analysis. DFT calculations continue to prove their worth in the prediction and interpretation of hyperfine coupling constants in (paramagnetic) radical species. The broader characterization of less fleeting (diamagnetic) molecules hosted in zeolites, either as deliberately introduced probes or as formed during catalytic activity, has been greatly aided by developments in infra-red (IR) spectroscopy, UV/Resonance Raman methods, inelastic neutron scattering techniques and NMR, as are surveyed in their recent applications to this topic.