IR spectroscopic measurement of diffusion kinetics of chemisorbed pyridine through nanocrystalline MgO particles. The involvement of surface defect sites in slow diffusion

The molecular transport of pyridine through nanosized MgO particles has been investigated by Fourier transform IR spectroscopy. Two regimes of chemisorbed pyridine diffusion are observed. A fast diffusion process is associated with pyridine bound to nondefective smooth MgO(100) facets which exhibit an activation energy barrier of 35.7 kJ mol ^-1 for escape into a mobile precursor. The slow pyridine diffusion process occurs from defect sites, where the activation energy of escape to the mobile precursor is measured to be 64.6 kJ mol ^-1. The escape barriers controlling pyridine diffusion through MgO powders are similar to the calculated adsorption energy on MgO(100) and to the calculated adsorption energies on various defect sites on MgO(100) havinglower Mg ²⁺ coordination numbers than those on MgO(100) facets.