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Item type:Publication, The skeletal isomerization in ferrierite: A theoretical assessment of the bi-molecular conversion of cis-butene to iso-butene(2013-03-01)Gleeson, DuangkamolIt is still not totally clear as to whether the skeletal isomerization of linear butenes to iso-butene in ferrierite occurs via a mono-molecular or bi-molecular process. To try and shed more light on this process, quantum chemical calculations were undertaken on both mechanisms. A large cluster model (H<inf>53</inf>O<inf>52</inf>Si<inf>35</inf>Al) has been employed here to study the bi-molecular process and these results are contrasted to the mono-molecular results previously reported by the author using the same model. The results suggest that a bi-molecular process can indeed result in the formation of iso-butene, as well as longer chained by-products as exemplified by 2,4,4-trimethylpent-2-ene. A rate determining step of 18.6 kcal/mol is found for the bi-molecular process, involving CC bond formation between the two monomers. The barrier is also predicted to be considerably lower than that of the mono-molecular reaction (24.5 kcal/mol). Nevertheless, given that 2,4,4-trimethylpent-2-ene has a considerably lower barrier to reaction, and is more energetically favourable, iso-butene product to might not be expected to form in large quantities via this route. © 2012 Elsevier B.V. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, A theoretical study of cis-trans isomerisation in H-ZSM5: Probing the impact of cluster size and zeolite framework on energetics and structure(2008-01-01)Gleeson, DuangkamolIn this study the results from a series of calculations are reported that probe the influence of the QM cluster size and the extended framework treatment in ONIOM calculations. This is done by comparing the differences in the structures and energetics obtained during simulations of cis-trans isomerisation of butene in H-ZSM-5 at varying level of accuracy. Seven different models have been employed; 3T, 5T and 10T DFT cluster models, and to more effectively encode the extended framework of ZSM-5; 3T:46T, 5T:46T, 10T:46T DFT:MM ONIOM models, and a 46T DFT cluster model. The results show that irrespective of the exact QM cluster size, relatively small gasphase clusters show clear limitations due to the neglect of the extended framework. In particular, the structural and electronic implications of using the different zeolite models have been rigorously assessed using the multivariate statistical method principal components analysis (PCA). © Springer Science+Business Media B.V. 2008. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Application of QM simulations and multivariate analysis in the study of alkene reactivity in the zeolite H-ZSM5(2008-01-01)Gleeson, DuangkamolReported herein are the results of an investigation into the effect of the extended framework of the zeolite ZSM-5 on the reaction energetics and structures of (a) the physisorbed complex formed between the zeolite and six alkenes, (b) the corresponding chemisorbed alkoxide intermediate and (c) the transition states (TS) connecting the two. For this, quantum mechanical (QM) simulations of ZSM-5 in the presence and absence of the zeolite framework have been employed. A 46T density functional theory (DFT) cluster model and a 3T:46T DFT:UFF ONIOM model are used to represent the former scenario and a simple 3T DFT cluster model for the latter. The structural implications of neglecting the zeolite framework have been rigorously compared using the multivariate statistical method principal components analysis (PCA). This method allows one to assess the correlated nature of the changes in structure along the reaction coordinate, for multiple different alkenes, in a facile, reliable way. Copyright © 2008 John Wiley & Sons, Ltd. - Some of the metrics are blocked by yourconsent settings
Item type:Publication, The catalytic conversion of acetonitrile to acrylonitrile in zeolitic systems: Rationalization of experimental observations using theoretical simulations(2007-12-15)