Description
Adsorption in zeolites is a complex process that involves multiple factors such as pore size, pore shape, and the interactions between the adsorbate and the zeolite framework. Especially, in small-pore zeolites, the close matching size of the molecules and the zeolite’s pore window strongly impacts adsorption, diffusion and catalytic conversion of molecules. This makes small-pore zeolites attractive adsorbents for industrial application such as methanol-to-olefins (MTO) conversion, selective catalytic reduction (SCR) of NOx, or light gas separations [1].As these factors have significant effects on the adsorption behavior and can make it challenging to accurately predict and understand the underlying mechanisms of adsorption in these small-pore zeolites. Modelling plays an important role in gaining insights into these underlying mechanisms, by providing predictions of adsorption and diffusion behavior within small-pore zeolites. Extensive computational studies have been performed on all-silica small-pore zeolites by various groups [2-4], elucidating the fundamental adsorption and diffusion behavior of molecules without intra-adsorbate or extra-framework interactions. However, limited experimental measurements, especially for unsaturated hydrocarbons, are available to validated these predictions, while the experimental validation of modelling of adsorption in zeolites is essential for ensuring the accuracy and reliability of these modelling predictions.
Our experimental study examines the zero coverage adsorption properties of n-alkanes and 1-alkenes in all-silica small-pore zeolites. By using inverse gas chromatograph (IGC), the zero coverage adsorption properties of adsorbates can be probed, allowing to deduce their fundamental adsorption behavior with the zeolite framework. All-silica variants of zeolite LTA (ITQ-29) and zeolite CHA (Si-CHA) were selected for characterization due to their industrial relevance. Using IGC, the Henry constants, adsorption enthalpy and entropy at zero coverage of hydrocarbons with up to 10 carbon atoms are determined between 30-320°C. In addition, in the case of Si-CHA, we qualitatively demonstrate the kinetic hindrance effect within the zeolite cage for non-linearized adsorbates up to carbon number 5. Subtle changes in adsorbate’s bond angle and bond length influences the diffusion through the narrow pore windows, allowing unsaturated linear hydrocarbons to adsorb rapidly, while saturated linear hydrocarbons are excluded from the zeolite. The experimental results of this study are compared with the modelling predictions made in the literature, and contribute to the enhanced understanding of adsorption properties in small-pore zeolites.
References
[1] Dusselier, M., Mark E. D., Chem. Rev. 118.11 (2018): 5265-5329.
[2] Dubbeldam, D., Berend S., J. Phys. Chem. B 107.44 (2003): 12138-12152.
[3] Ter Horst, J. H., et al., Microporous Mesoporous Mater. 53.1-3 (2002): 45-57.
[4] Luna-Triguero, A., et al., J. Phys. Chem. C 119.33 (2015): 19236-19243.
| Period | 18 May 2023 |
|---|---|
| Event title | 1st Mediterranean Conference on Porous Materials |
| Event type | Conference |
| Conference number | 1 |
| Location | Greece |
| Degree of Recognition | International |