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

Abstract

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 CO 2 , 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 RHOfamily, and show that by combining diffraction data, lattice fluid modelling and dynamic column experiments, we obtain a plausible mechanism for CO 2 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.

Gating effect for gas adsorption in microporous materials—mechanisms and applications

“…The gas adsorption isotherms of CO ). 109 The RALF model allows for the structural change within the lattice, which can be predicted based on the different densities and Gibbs energies of different structural configurations. 110 Therefore, it can successfully fit the isotherms showing the gating effect.…”

“…110 Therefore, it can successfully fit the isotherms showing the gating effect. 109,110 The predicted adsorption amount at the abruptly rising point in the isotherm can be further applied in the kinetics model. 109 To derive a quantitative model that can describe the temperature-regulated gate-opening process of trapdoor materials, Li et al introduced two new parameters T 0 and b, which represent the cumulative probability that a given pore-keeping ion will admit a guest molecule.…”

Cation Control of Cooperative CO2 Adsorption in Li-Containing Mixed Cation Forms of the Flexible Zeolite Merlinoite

“…Zeolite Rho and higher members of the extended RHO family of small-pore zeolite structures have been observed to give CO 2 isotherms with noticeable inflections and steps when suitably cation-exchanged (Na- and Cs-Rho, Na- and Cs-forms of ZSM-25 and PST-20, for example). − For Cs-Rho, there is slow movement of Cs cations from D8R to S8R sites that results in a sluggish change of phase and increase in uptake, while in ZSM-25, there is a stepped increase in uptake that offers appreciable CO 2 uptake over a narrow pressure range. ZSM-25 displays a reversible unit cell volume increase related to the adsorption step, but the framework is too complex for the structural mechanism to be fully resolved.…”

Accurate blank corrections for zero length column experiments

“…CO 2 on templated (Na,TEA)-ZSM-25. This system exhibits a stepped isotherm and constitutes a significant deviation from linearity at 20% CO 2 and 35 °C (as described in detail in Min et al 2018;Verbraeken et al 2020)). The ZLC desorption data for a measurement at low flow rate is shown in Fig.…”