Zeolite 13X is an excellent candidate for the capture of CO2. However, this system needs to be investigated in more detail with regard to adsorption and diffusion. For this purpose, frequency response (FR) measurements were carried out with binderless zeolite 13X (NaMSX) and CO2. The size of the particles and the sample amount were modified in order to investigate their effects on diffusion processes. Macropore diffusion was detected and the corresponding diffusion coefficients were determined. The mentioned system was additionally used to evaluate the performance of the in-house FR apparatus.