Gas transport in porous solids has been an important issue, which is popular in a large range of industrial sectors, especially chemical engineering. Transport by gas diffusion in microporous materials plays an important role in the optimization and development of industrial applications. In recent years, electrochemical impedance spectroscopy (EIS) has become a powerful tool to study materials via electrical properties, polarization phenomena, and mass and charge transfer.
The thesis deals with gas phase diffusion in porous solids by applying the EIS method. The adsorption and diffusion processes have been studied at low temperatures. In order to enhance the contribution of gas phase diffusion by EIS effectively, the experimental measurements are carried out at the same conditions as those of the diffusion-controlled process. Some significant improvements are made such as the application of high AC voltage for measurements, the preparation procedure of the sample to reduce noisy points on the impedance spectra. For the purpose of determining transport coefficients a new theoretical approach is developed based on only impedance data. Additionally, FTIR spectroscopy and TG/DTG are combined to study the surfaces of materials and the adsorption of substances as well as the amount of adsorbed water existing in the samples. The experiments have been conducted with both gas phases and vapors, which includes ammonia, water, isopropanol, n-butane, iso-butane, and carbon dioxide which are adsorbed on three porous solids: sulfated zirconia, zeolite type 5A, and zeolite H-ZSM5.