Combined NMR cryoporometry, relaxometry and diffusometry were applied to characterize porous carbon materials. Pore space characterization in NMR cryoporometry is based on the measurement of melting point depression of the confined liquids, whereas NMR relaxometry and diffusometry explore the random motion of the molecules under confinement by the pore space. We demonstrate compatibility between the evidence of classical sorption experiments and NMR cryoporometry on pore size distribution. There is a distribution in both the nuclear magnetic relaxation rates and diffusion coefficients. These distributions have to be referred to heterogeneities in the pore space. Since they can only be observed if their influence is not averaged out on the diffusion paths covered by the molecules during the respective measurements, the spatial extension of the regions with structural differences (as evidenced by the differences in diffusion and nuclear magnetic relaxation of the probe molecules) may be estimated to be at least of the order of 20μm.

The diffusion of n-decane, n-heptadecane and their binary mixtures of two different compositions confined in novel mesoporous aluminosilicates was investigated by the Pulsed Field Gradient (PFG) NMR technique. The temperature range studied was between −100 and 23°C, comprising the bulk melting points of n-heptadecane at 23°C and n-decane at −30°C. The melting curves of all liquids measured by cryo-NMR allowed discrimination of the temperature ranges where non-frozen liquid existed in the pores. The study of n-decane and n-heptadecane mixtures of two different compositions by cryo-NMR does not reveal any preferential adsorption of one of the mixture components in the investigated material. In both the bulk and the pores, the diffusion coefficients follow Arrhenius dependencies with essentially identical activation energies. The diffusion coefficients of the liquids inside the pores are reduced by more than an order of magnitude.

A new method to determine the surface permeability of nanoporous particles is proposed. It is based on the comparison of experimental data on tracer exchange and intracrystalline molecular mean square displacements as obtained by the PFG NMR tracer desorption technique with the corresponding solutions of the diffusion equation via dynamical Monte Carlo simulations. The method is found to be particularly sensitive in the "intermediate" regime, when the influence of intracrystalline diffusion and surface resistances of the nanoporous crystal on molecular transport are comparable and the conventional method fails. As an example, the surface permeabilities of two samples of zeolite NaCaA with different crystal sizes are determined with methane, as a probe molecule, at room temperature.

The surface permeability of zeolite crystals of type NaCaA for small alkane molecules (methane and ethane) was estimated by using a novel method, analysing NMR tracer desorption measurements. It is based on the measurement of both the relative amount of tracer exchange and the corresponding effective coefficients of intracrystalline diffusion and their correlation with the results of model calculations by dynamic Monte Carlo simulations. For the two LTA specimens investigated, already in the as-synthesized zeolite crystals notable surface resistances have been observed. Surface permeabilities have been studied in dependence on temperature, sorbate and crystal size.