Discovery of an Optimal Porous Crystalline Material for the Capture of Chemical Warfare Agents

Chemical warfare agents (CWAs) are regarded as a critical challenge in our society. Here, we use a high-throughput computational screening strategy backed up by experimental validation to identify and synthesize a promising porous material for CWA removal under humid conditions. Starting with a database of 2,932 existing metal-organic framework (MOF) structures, we selected those possessing cavities big enough to adsorb well-known CWAs such as sarin, soman, and mustard gas as well as their nontoxic simulants. We used Widom method to reduce significantly the simulation time of water adsorption, allowing us to shortlist 156 hydrophobic MOFs where water will not compete with the CWAs to get adsorbed. We then moved to grand canonical Monte Carlo (GCMC) simulations to assess the removal capacity of CWAs. We selected the best candidates in terms of performance but also in terms of chemical stability and moved to synthesis and experimental breakthrough adsorption to probe the predicted, excellent performance. This computational-experimental work represents a fast and efficient approach to screen porous materials in applications that involve the presence of moisture

Zeolites for CO2–CO–O2 Separation to Obtain CO2-Neutral Fuels

Carbon dioxide release has become an important global issue due to the significant and continuous rise in atmospheric CO2 concentrations and the depletion of carbon-based energy resources. Plasmolysis is a very energy-efficient process for reintroducing CO2 into energy and chemical cycles by converting CO2 into CO and O2 utilizing renewable electricity. The bottleneck of the process is that CO remains mixed with O2 and residual CO2. Therefore, efficient gas separation and recuperation are essential for obtaining pure CO, which, via water gas shift and Fischer–Tropsch reactions, can lead to the production of CO2-neutral fuels. The idea behind this work is to provide a separation mechanism based on zeolites to optimize the separation of carbon dioxide, carbon monoxide, and oxygen under mild operational conditions. To achieve this goal, we performed a thorough screening of available zeolites based on topology and adsorptive properties using molecular simulation and ideal adsorption solution theory. FAU, BRE, and MTW are identified as suitable topologies for these separation processes. FAU can be used for the separation of carbon dioxide from carbon monoxide and oxygen and BRE or MTW for the separation of carbon monoxide from oxygen. These results are reinforced by pressure swing adsorption simulations at room temperature combining adsorption columns with pure silica FAU zeolite and zeolite BRE at a Si/Al ratio of 3. These zeolites have the added advantage of being commercially available.</p

Improving Ammonia Production Using Zeolites

Ammonia is one of the most important compounds in the chemical industry as it is the main raw material in the production of fertilizers. Its production is achieved using the Haber-Bosch process, where nitrogen and hydrogen react in the presence of a catalyst producing a mixture containing ammonia. In this work we use molecular simulations to study the effect of confinement on the ammonia synthesis reaction in pure silica zeolites FER, MOR, MFI, BEA, LTA, and FAU. We calculated adsorption isotherms and isobars of the components resulting from the reaction for a wide range of values of pressure and temperature. The removal of the resulting ammonia will keep the equilibrium of the reaction favoring ammonia formation at lower values of pressure than in conventional plants. Among the studied zeolites, FAU and ITQ-9 are preferred for ammonia storage because of their higher adsorption capacity. The effect of confinement is proven to increase ammonia production, being the zeolites with the narrowest pores (FER and MFI) the ones that exhibit the highest conversion of the reactants. Besides, we found that the optimal working conditions for the production process in confinement are 573 K and 200 bar. At these particular conditions, the production of ammonia increases without the addition of any extra operational costs to the process

Role of hydrogen bonding in the capture and storage of ammonia in zeolites

Ammonia is an important chemical compound used in a wide range of applications. This makes its capture, purification and recovery necessary. We combine experimental and molecular simulation techniques to identify the molecular mechanisms ruling the adsorption of ammonia in pure and high silica zeolites. To reproduce accurately the interaction between ammonia and the zeolites the development of a transferable set of Lennard-Jones parameters was needed. Adsorption isotherms were measured and also calculated using the new set of parameters for several commercial pure silica zeolites, including MFI, FAU, and LTA topologies. We found an anomalous behavior of the adsorption isotherm of ammonia in MFI, which can be explained through a monoclinic to orthorhombic structural phase transition. We also found that low concentration of extra-framework cations favors the adsorption of ammonia in these high silica zeolites. Using radial distribution functions and hydrogen bond analyses we identified ammonia clusterization as the key mechanism involved in the adsorption. Based on it, hydrophobic zeolites with large pores could be used for ammonia sequestration with lower cost than the currently used techniques

Identifying zeolite topologies for storage and release of hydrogen

We present a molecular simulation study on the most suitable zeolite topologies for hydrogen adsorption and storage. We combine saturation capacities, pore size distributions, preferential adsorption sites, and curves of heat of adsorption of hydrogen as a function of temperature (we call them heats of adsorption (HoA)-curve) to identify the optimal zeolites for storage and release of hydrogen. Then, we analyze the relation between the shape of the HoA-curve and the topology of the materials. We also evaluate the influence of incorporating Feynman-Hibbs effect on the adsorption behavior. We can establish different shapes on the HoA-curve depending on the uniformity or not of the pores of the zeolites. Parabola-like curves are observed in structures with one or similarly sized pores, whereas deviations from the parabola are found at low temperature for structures combining large and small pores. The Feynman-Hibbs quantum correction reduces the adsorption capacity of the materials affecting not only the saturation capacity but also the shape of the isotherms. From our results, the zeolites studied in this work can be considered potential candidates for the storage and release of hydrogen.Accepted Author ManuscriptEngineering Thermodynamic

Zeolite screening for the separation of gas mixtures containing SO 2 , CO 2 and CO

International audienc

Role of hydrogen bonding in the capture and storage of ammonia in zeolites

Ammonia is an important chemical compound used in a wide range of applications. This makes its capture, purification and recovery necessary. We combine experimental and molecular simulation techniques to identify the molecular mechanisms ruling the adsorption of ammonia in pure and high silica zeolites. To reproduce accurately the interaction between ammonia and the zeolites the development of a transferable set of Lennard-Jones parameters was needed. Adsorption isotherms were measured and also calculated using the new set of parameters for several commercial pure silica zeolites, including MFI, FAU, and LTA topologies. We found an anomalous behavior of the adsorption isotherm of ammonia in MFI, which can be explained through a monoclinic to orthorhombic structural phase transition. We also found that low concentration of extra-framework cations favors the adsorption of ammonia in these high silica zeolites. Using radial distribution functions and hydrogen bond analyses we identified ammonia clusterization as the key mechanism involved in the adsorption. Based on it, hydrophobic zeolites with large pores could be used for ammonia sequestration with lower cost than the currently used techniques.The research leading to these results has received funding from the Spanish Ministerio de Economía y Competitividad (CTQ2016-80206-P) and Ministerio de Ciencia, Innovación y Universidades (CTQ2017-92173-EXP). We thank C3UPO for the HPC support. JMVL thanks the financial support of the ERC project ZEOSEP (Ref. 779792)

Adsorption equilibrium of nitrogen dioxide in porous materials

The effect of confinement on the equilibrium reactive system containing nitrogen dioxide and dinitrogen tetroxide is studied by molecular simulation and the reactive Monte Carlo (RxMC) approach. The bulk-phase reaction was successfully reproduced and five all-silica zeolites (i.e. FAU, FER, MFI, MOR, and TON) with different topologies were selected to study their adoption behavior. Dinitrogen tetroxide showed a stronger affinity than nitrogen dioxide in all the zeolites due to size effects, but exclusive adsorption sites in MOR allowed the adsorption of nitrogen dioxide with no competition at these sites. From the study of the adsorption isotherms and isobars of the reacting mixture, confinement enhanced the formation of dimers over the full range of pressure and temperature, finding the largest deviations from bulk fractions at low temperature and high pressure. The channel size and shape of the zeolite have a noticeable influence on the dinitrogen tetroxide formation, being more important in MFI, closely followed by TON and MOR, and finally FER and FAU. Preferential adsorption sites in MOR lead to an unusually strong selective adsorption towards nitrogen dioxide, demonstrating that the topological structure has a crucial influence on the composition of the mixture and must be carefully considered in systems containing nitrogen dioxide.Accepted Author ManuscriptEngineering Thermodynamic

Identifying Zeolite Topologies for Storage and Release of Hydrogen

We present a molecular simulation study on the most suitable zeolite topologies for hydrogen adsorption and storage. We combine saturation capacities, pore size distributions, preferential adsorption sites, and curves of heat of adsorption of hydrogen as a function of temperature (we call them heats of adsorption (HoA)-curve) to identify the optimal zeolites for storage and release of hydrogen. Then, we analyze the relation between the shape of the HoA-curve and the topology of the materials. We also evaluate the influence of incorporating Feynman–Hibbs effect on the adsorption behavior. We can establish different shapes on the HoA-curve depending on the uniformity or not of the pores of the zeolites. Parabola-like curves are observed in structures with one or similarly sized pores, whereas deviations from the parabola are found at low temperature for structures combining large and small pores. The Feynman–Hibbs quantum correction reduces the adsorption capacity of the materials affecting not only the saturation capacity but also the shape of the isotherms. From our results, the zeolites studied in this work can be considered potential candidates for the storage and release of hydrogen