Dr Robert Bell
Our research revolves around two main themes: (1) Understanding the structure and properties of zeolites, and other framework materials, from a topological perspective. (2) Modelling the adsorption and diffusion of small molecules, including carbon dioxide, in microporous materials.
Framework Topology and Zeolites
Zeolites are microporous solids, containing pores and cavities of molecular dimensions. Their crystal structures can be thought of in terms of regular frameworks, or nets in which all the atoms are connected together by chemical bonds. Uniquely, zeolites possess four-connected nets in which four-coordinate atoms are linked together by two-coordinate bridging atoms. Currently, about 150 or so different types of framework structure are known, either in minerals or synthetic zeolites, but there are potentially a great many more, whose structures can be enumerated using topological and geometric principles, but which have not yet been synthesised.
Our interest is in studying hypothetical structures, generated by mathematical methods, and in predicting which of them are feasible to make, and what their properties might be. We have shown that only a small fraction of hypothetical zeolites are likely to be realised as silicates, and also that certain geometric motifs are disfavoured because they give rise to unphysical distortion of the tetrahedral coordination sphere. Currently we are exploring the effect of varying composition on the preference for certain common AX 2 topologies.
Simulating Adsorption in Microporous materials
The ability of microporous materials to admit molecules into their inner cavities has led to many applications in the area of gas adsorption and separation. Using computational chemistry methods, including the Monte Carlo method, we able to simulate the adsorption behaviour of these materials under different conditions of temperature and pressure. Our interest is in the adsorption of polar and polarisable molecules into heterogeneous sorbents, e.g. zeolites containing metal ions, where there is strong binding at specific sites in the adsorbing material. These adsorbents are increasingly important as they may be able to selectively adsorb carbon dioxide, as well as other environmentally harmful molecules, from mixed gas streams. In addition they present a challenge to existing computational methods. We are now also looking at adsorption within flexible Metal Organic framework materials (MOFs) which hold the possibility of low-mass storage materials.
- "Chemical evaluation of hypothetical uninodal zeolites", M.D. Foster, O. Delgado-Friedrichs, R.G. Bell, F.A.A. Paz & J Klinowsk i, J. Am Chem. Soc., 126, 9769 (2004)
- "Chemically feasible hypothetical crystalline networks", M.D. Foster, A. Simperler, R.G. Bell, O. Delgado-Friedrichs, F.A.A. Paz & J Klinowsk i , Nature Materials, 3, 234 (2004)
- "Cation mobility and the sorption of chloroform in zeolite NaY: a molecular dynamics study ", N.A. Ramsahye & R.G. Bell, J. Phys. Chem. B, 109, 4738 (2005)
- "Tetrahedral distortion and energetic packing penalty in "Zeolite" frameworks; linked phenomena?", M. Zwijnenberg, A. Simperler, S.A. Wells & R.G. Bell, J. Phys. Chem. B, 109, 14783 (2005).
- "Adsorption mechanism of carbon dioxide in faujasites: Grand canonical Monte Carlo simulations and microcalorimetry measurements", G. Maurin, P. Llewellyn & R.G. Bell, J. Phys. Chem. B, 109, 16084 (2005).
- “A computational study into the (tetrahedral) distortion of TX 2 alpha-quartz materials: The effect of changing the chemical composition away from SiO 2 “, M.A. Zwijnenburg, R. Huenerbein, R.G. Bell & F. Cora, J. Solid State Chem., 179, 3429 (2006)
- “ Diffusion of methanol in zeolite NaY: a molecular dynamics study “, D.F. Plant, G. Maurin & R.G. Bell, J. Phys. Chem. B, 111, 2836 (2007).
- “ Dramatic Differences between the Energy Landscapes of SiO 2 and SiS 2 Zeotype Materials”, M.A. Zwijnenburg, F. Cora & R.G. Bell, J. Am. Chem. Soc., 129, 12588 (2007).