Understanding CO2 adsorption in a flexible zeolite through a combination of structural, kinetic and modelling techniques

•Adsorption equilibrium and kinetics measured for CO2 on ZSM-25.•Combination of zero length column and structural data used to understand the mechanism of diffusion in flexible zeolite.•Kinetic model fully parametrized to reflect structure change and opening of secondary cages during CO2 adsorption. In this study we show how non-trivial equilibrium and kinetic adsorption behaviour in a flexible zeolite can be understood through a combination of experimental characterisation and modelling. Flexible zeolites, such as those in the RHO-family, can exhibit unusual stepped isotherms in the presence of CO2, but their structural complexity makes it hard to attribute a clear mechanism. Here we present a structural and kinetic study on (Na,TEA)-ZSM-25, an extended member of the RHO-family, and show that by combining diffraction data, lattice fluid modelling and dynamic column experiments, we obtain a plausible mechanism for CO2 adsorption and transport in this material. It is evident that by using any single technique, the behaviour is too complex to be readily understood. This is to our knowledge the first study to measure and model the changing kinetics due to adsorption induced framework flexibility.