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In this thesis we use molecular simulations to¨ study adsorption and diffusion properties of gases ¨in nanoporous materials. We focus on gases with e nvironmental relevance and study them in processes ¨that can be used to reduce the emission of certai n pollutants. We use zeolites and MOFs as adsorben ts. These materials are well known and have many i ndustrial applications making them good candidates ¨for the processes under study. In our simulations ¨we make use not only of available force fields in ¨the literature but we also develop new ones. We s tudy the mechanisms that rule the adsorption and d iffusion behaviours as well as the distribution of ¨molecules inside the structures. All the studies¨ have been performed using the methods and models d escribed in section 3.Influence of the topo logy in adsorption and separation processes of gre enhouse gases and pollutants (Chapters 2 and 3)In chapter 2 we use previously published force ¨fields and models to study the adsorptive separat ion of a natural gas mixture in MOFs. For that pur pose we study the adsorption behaviour of the main ¨components of natural gas (CH4, C2H6, C3H8, CO2,¨ N2) in two well-known metal-organic frameworks (Cu -BTC and IRMOF-1). Based on the different topologi es and the distribution of the molecules inside th ese two structures, each of them will be suitable¨ for a different purpose.Once the efficiency ¨of Cu-BTC in separation processes is proved, in c hapter 3 we study the performance of this material ¨on the separation of CCl4 from air. To this aim,¨ we study adsorption and diffusion properties of th ese molecules inside the structure. In addition, w e propose a selective blockage of the structure to ¨enhance its selectivity in the separation process .Effect of humidity into adsorption and sep aration processes (Chapters 4 and 5)To prog ress further with the study of removal of CCl4 fro m air, in chapter 4 we discuss the effect of relat ive air humidity on the separation process. To thi s aim, we first discuss the models of the molecule s under study. Then we analyse the influence of di fferent percentages of relative air humidity in the removal of CCl4 using Cu-BTC from the adsorption ¨and diffusion behaviours of the gas mixture.In chapter 5 we investigate the effect of water¨ on the adsorption of CO in metal-organic framework s. After discussion of the available models of CO¨ and their adsorption behaviour in Cu-BTC, IRMOF-1¨ and MIL-47, we propose a new model for CO. Finally , we study the influence of water in both Cu-BTC a nd IRMOF-1 during the adsorption process.Ad sorption of gases in presence of extra-framework c ations (Chapters 6 and 7)In chapter 6 we st udy the adsorption of CO2 in zeolites containing a luminium. Depending on the Si/Al ratio complexes b etween CO2 and the extra-framework cations are for med interacting with the structure. In this work w e investigate such effect in FAU and LTA zeolites¨ by combining experimental and simulation technique s. From the simulation point of view we use an ava ilable transferable force field to define the inte ractions of CO2 with the structures and provide a¨ new set of parameters to reproduce these interacti ons when complexes are formed.Not many tran sferable force fields are available in the literat ure to study the adsorption of some molecules in z eolites. In chapter 7 we use previously available¨ models for CH4 and Ar and provide new ones for O2, ¨N2 and CO to study their adsorption behaviour in¨ both pure silica and aluminosilicates.Separ ation of enantiomers (Chapters 8 and 9)Anot her separation process of industrial interest is t he separation of enantiomers from racemic mixtures . In chapter 8 we investigate the enantioselective¨behaviour of zeolites during the adsorption of sm all polar molecules, such as CHClFBr. From previou s works with non-polar molecules the need for cati ons to induce a selective behaviour in MFI zeolite ¨was observed. Hence, we study the same effect alo ng with topological effects of adsorption on MFI,¨ MEL, FER and TON zeolites.In chapter 9 we u se the knowledge obtained from the previous chapte r to describe the mechanisms that govern adsorptio n behaviour of enantiomeric mixtures of lactic aci d in MFI zeolites.The main conclusions from¨the studies are:Regarding the influence of ¨topology in the adsorption / separation of greenh ouse gases and other pollutants, it has been found¨that structures with large cavities as IRMOF-1 we re proved to be suitable materials for storage pro cesses. On the other hand, structures combining di fferent size of cavities such as Cu-BTC show promi sing results in separation processes. Dependi ng on the distribution of the molecules inside the ¨structure and considering the competition of the¨ molecules for specific adsorption sites, it is pos sible to enhance or to dismiss the selectivity of¨ a framework for certain gases blocking specific ad sorption sites of the structure.In the stud y the effect of humidity in adsorption and separat ion processes, it was found that an interesting op tion to modify the behaviour of a given porous mat erial is by taking into account the humidity of th e environment. The water stability of porous mater ials is a delicate point as some of them lose thei r crystallinity when water attacks the metallic ce ntres. For this reason it is important to quantify ¨the maximal water uptake of a given framework wit hout affecting its structure. Combining different¨ contents of water with the topology and the polari ty of the molecule under study it is possible to i ncrease or to reduce the adsorption.Regardi ng the adsorption of gases in the presence of cati ons, the presence of extra-framework cations in th e structures increases even more the need of detai led studies of the systems. It is important to und erstand the effect that density, chemical potentia l and mobility of the cations exert on the adsorpt ion.In studies of separation of enantiomers , has been found that achiral zeolites can be ¨used for the separation of chiral compounds (scal emic mixtures). The separation of enantiomeric mix tures is very sensitive to the presence of extra-f ramework cations, their distribution inside the st ructures and the topology of the zeolites as a fun ction of the size, shape and polarity of the adsor bates.Finally, as a general conclusion of t his work, molecular simulation techniques have been proved to be very useful tools to understand ads orption and diffusion mechanisms. It is essential¨ to have realistic models and force fields that are ¨able to reproduce the experimental behaviour of s ystems. As a result, the acquired knowledge c an be used to determine the best materials and con ditions in order to enhance the efficiency of a va riety of processes with environmental or industria l relevance.