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  • 1.
    Brant Carvalho, Paulo H. B.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bull, Craig L.
    Funnell, Nicholas P.
    Tulk, Chris A.
    Andersson, Ove
    Häussermann, Ulrich
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Elucidation of the pressure induced amorphization of tetrahydrofuran clathrate hydrate2019In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 150, no 20, article id 204506Article in journal (Refereed)
    Abstract [en]

    The type II clathrate hydrate (CH) THF center dot 17 H2O (THF = tetrahydrofuran) is known to amorphize on pressurization to similar to 1.3 GPa in the temperature range 77-140 K. This seems to be related to the pressure induced amorphization (PIA) of hexagonal ice to high density amorphous (HDA) ice. Here, we probe the PIA of THF-d(8)center dot 17 D2O (TDF-CD) at 130 K by in situ thermal conductivity and neutron diffraction experiments. Both methods reveal amorphization of TDF-CD between 1.1 and 1.2 GPa and densification of the amorphous state on subsequent heating from 130 to 170 K. The densification is similar to the transition of HDA to very-high-density-amorphous ice. The first diffraction peak (FDP) of the neutron structure factor function, S(Q), of amorphous TDF-CD at 130 K appeared split. This feature is considered a general phenomenon of the crystalline to amorphous transition of CHs and reflects different length scales for D-D and D-O correlations in the water network and the cavity structure around the guest. The maximum corresponding to water-water correlations relates to the position of the FDP of HDA ice at similar to 1 GPa. Upon annealing, the different length scales for water-water and water-guest correlations equalize and the FDP in the S(Q) of the annealed amorph represents a single peak. The similarity of local water structures in amorphous CHs and amorphous ices at in situ conditions is confirmed from molecular dynamics simulations. In addition, these simulations show that THF guest molecules are immobilized and retain long-range correlations as in the crystal.

  • 2.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Liu, Qingling
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Adsorption kinetics for CO2 on highly selective zeolites NaKA and nano-NaKA2013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, p. 1326-1336Article in journal (Refereed)
    Abstract [en]

    Carbon dioxide removal from flue gas via swing adsorption processes requires adsorbents with a high CO2 selectivity and capacity. These properties are particularly valuable to reduce the cost of carbon capture and storage (CCS). Zeolite NaKA was studied for its ability to selectively adsorb CO2 from flue gas, as we previously observed that zeolite NaKA, with a K+/(K+ + Na+) ratio of 17 atomic%, was highly selective towards CO2 over N-2 adsorption by tuning the size of the pore window apertures [1]. The reduced pore apertures may, however, retard the adsorption rate of CO2. Here, we studied the kinetics of CO2 adsorption on regularly sized zeolite NaKA and on nano-sized zeolite NaKA. We used in situ infrared (IR) spectroscopy and observed that CO2 physisorbed relatively rapidly. Density functional theory (DFT) was used for quantum chemical calculations, and the results indicated that CO2 molecules bridged across two or three Na+ ions in the samples with no or very small amount of K. When more K+ ions are present the CO2 molecules no longer bridged across multiple metal ions and adopted an end-on configuration. The calculation showed a shift in the stretching vibration frequency of physisorbed CO2 as observed by IR spectroscopy. Nano-sized zeolite NaKA were synthesised and studied to improve the rate of CO2 adsorption, as the diffusion rate typically increases quadratically with decreasing particle size. Still, the CO2 adsorption rate on nano-sized zeolites NaA and NaKA did not increase significantly. For nano-sized zeolite NaA, we speculate that the absence of such an increased rate is an effect from a skin layer that had formed on the nano-sized zeolite NaA, a layer that was possibly related to intergrowths with extremely small crystals on the surface. The apparently slow adsorption kinetics of CO2 on nano-sized zeolite NaKA was more difficult to explain because it could relate to imperfections within the small crystals, remaining water, or other effects. Overall, the CO2 adsorption rates on zeolite NaKA crystals of different sizes were fast and relevant for the time scales required for adsorption based CCS processes, such as vacuum and temperature swing adsorption (VSA/TSA).

  • 3.
    Cheung, Ocean
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Bacsik, Zoltán
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Krokidas, Panagiotis
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Materials Chemistry.
    K+ Exchanged Zeolite ZK-4 as a Highly Selective Sorbent for CO22014In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 30, no 32, p. 9682-9690Article in journal (Refereed)
    Abstract [en]

    Adsorbents with high capacity and selectivity for adsorption of CO2 are currently being investigated for applications in adsorption-driven separation of CO2 from flue gas. An adsorbent with a particularly high CO2-over-N-2 selectivity and high capacity was tested here. Zeolite ZK-4 (Si:Al similar to 1.3:1), which had the same structure as zeolite A (LTA), showed a high CO2 capacity of 4.85 mmol/g (273 K, 101 kPa) in its Na+ form. When approximately 26 at % of the extraframework cations were exchanged for K+ (NaK-ZK-4), the material still adsorbed a large amount of CO2 (4.35 mmol/g, 273 K, 101 kPa), but the N-2 uptake became negligible (<0.03 mmol/g, 273 K, 101 kPa). The majority of the CO2 was physisorbed on zeolite ZK-4 as quantified by consecutive volumetric adsorption measurements. The rate of physisorption of CO2 was fast, even for the highly selective sample. The molecular details of the sorption of CO2 were revealed as well. Computer modeling (Monte Carlo, molecular dynamics simulations, and quantum chemical calculations) allowed us to partly predict the behavior of fully K+ exchanged zeolite K-ZK-4 upon adsorption of CO2 and N-2 for Si:Al ratios up to 4:1. Zeolite K-ZK-4 with Si:Al ratios below 23:1 restricted the diffusion of CO2 and N-2 across the cages. These simulations could not probe the delicate details of the molecular sieving of CO2 over N-2. Still, this study indicates that zeolites NaK-ZK-4 and K-ZK-4 could be appealing adsorbents with high CO2 uptake (similar to 4 mmol/g, 101 kPa, 273 K) and a kinetically enhanced CO2-over-N-2 selectivity.

  • 4.
    Hu, Shichao
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Johnsson, Mats
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Gnezdilov, Vladimir
    Lemmens, Peter
    Tapp, Joshua
    Möller, Angela
    Crystal Structure and Magnetic Properties of the S=1/2 Quantum Spin System Cu-7(TeO3)(6)F-2 with Mixed Dimensionality2014In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, no 14, p. 7661-7667Article in journal (Refereed)
    Abstract [en]

    The new oxofluoride Cu-7(TeO3)(6)F-2 has been synthesized by hydrothermal synthesis. It crystallizes in the triclinic system, space group P (1) over bar. The crystal structure constitutes a Cu-O framework with channels extending along [001] where the F- ions and the stereochernically active lone-pairs on Te4+ are located. From magnetic susceptibility, specific heat, and Raman scattering measurements we find evidence that the magnetic degrees of freedom of the Cu-O-Cu segments in Cu-7(TeO3)(6)F-2 lead to a mixed dimensionality with single Cu S = 1/2 moments wealdy coupled to spin-chain fragments. Due to the weaker coupling of the single moments, strong fluctuations exist at elevated temperatures, and long-range magnetic ordering evolves at comparably low temperatures (T-N = 15 K).

  • 5.
    Ibarra, Ilich A.
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Universidad Nacional Autónoma de México, Mexico.
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Yang, Sihai
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Lee, Sukyung
    Chang, Jong-San
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Schröder, Martin
    Zou, Xiaodong
    Adsorption Properties of MFM-400 and MFM-401 with CO2 and Hydrocarbons: Selectivity Derived from Directed Supramolecular Interactions2016In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 55, no 15, p. 7219-7228Article in journal (Refereed)
    Abstract [en]

    ([Sc-2(OH)(2)(BPTC)]) (H4BPTC = biphenyl-3,3',5,5'-tetracarboxylit acid), MFM-400 (MFM = Manchester Framework Material; previously designated NOTT), and ([Sc(OH)-(TDA)]) (H(2)TDA = thiophene-2,5-dicarboxylic acid), MFM-401, both show xelective and, reversible capture of CO2. In particular, MFM-400 exhibits a reasonably high CO2 uptake at low pressures and competitive CO2/N-2 selectivity coupled to a moderate isosteric heat of adsorption (Q(st)) for CO2 (29.5 kJ mol(-1)) at zero coverage, thus affording a facile uptake release process. Grand canonical Monte Carlo (GCMC) and density functional theory (DFT) computational analyses of CO2 uptake in both materials confirmed preferential adsorption sites consistent with the higher CO2 uptake observed experimentally for MFM-400 over MFM-401 at low pressures. For MFM-400, the Sc-OH group participates in moderate interactions with CO2 (Q(st) = 33.5 kJ mol(-1)), and these are complemented by weak hydrogen-bonding interactions (O center dot center dot center dot H-C = 3.10-3.22 angstrom) from four surrounding aromatic -CH groups. In the case of MFM-401, adsorption is provided by cooperative interactions of CO2 with the Sc-OH group and one C-H group. The binding energies obtained by DFT analysis for the adsorption sites for both materials correlate well with the observed moderate isosteric heats of adsorption for CO2. GCMC simulations for both materials confirmed higher uptake of EtOH compared with nonpolar vapors of toluene and. cydohexane. This is in good Correlation with the experimental data, and DFT analysis confirmed the formation of a strong hydrogen bond between EtOH and the hydrogen atom of the hydroxyl group of the MFM-400 and MFM-401 framework (FIAT) with H-O-EtOH center dot center dot center dot H-O-FW distances of 1.77 arid 1.75 angstrom, respectively. In addition, the accessible regeneration of MFM-400 and MFM-401 and release of CO2 potentially provide minimal economic and environmental penalties.

  • 6. Kampouri, Stavroula
    et al.
    Nguyen, Tu N.
    Ireland, Christopher P.
    Valizadeh, Bardiya
    Ebrahim, Fatmah Mish
    Capano, Gloria
    Ongari, Daniele
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Ecole Polytechnique Fédérale de Lausanne (EPFL Valais), Switzerland.
    Guijarro, Nestor
    Sivula, Kevin
    Sienkiewicz, Andrzej
    Forró, László
    Smit, Berend
    Stylianou, Kyriakos C.
    Photocatalytic hydrogen generation from a visible-light responsive metal-organic framework system: the impact of nickel phosphide nanoparticles2018In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 6, no 6, p. 2476-2481Article in journal (Refereed)
    Abstract [en]

    Herein, we report the performance of a photocatalytic system based on visible-light active MIL-125-NH2 mixed with nickel phosphide (Ni2P) nanoparticles. This combination boosts the H-2 evolution rate to an outstanding value of 894 mu mol h(-1) g(-1) under visible-light irradiation, which is among the highest H-2 evolution rates reported to date for metal-organic frameworks (MOFs). The H-2 generation rate exhibited by Ni2P/MIL-125-NH2 is almost 3 times higher than that of the Pt/MIL-125-NH2 system, highlighting the impact of the co-catalyst on photocatalytic water splitting. Additionally, our system outperforms the Ni2P/TiO2 system under UV-vis irradiation. The exceptional performance of Ni2P/MIL-125-NH2 is due to the efficient transfer of photogenerated electrons from MIL-125-NH2 to Ni2P, high intrinsic activity of Ni2P and exceptional synergy between them. This system exhibits the highest apparent quantum yields of 27.0 and 6.6% at 400 and 450 nm, respectively, ever reported for MOFs.

  • 7.
    Keshavarzi, Neda
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mashayekhy Rad, Farshid
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Ansari, Farhan
    Akhtar, Farid
    Nilsson, Ulrika
    Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.
    Berglund, Lars
    Bergström, Lennart
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Nanocellulose-Zeolite Composite Films for Odor Elimination2015In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 7, no 26, p. 14254-14262Article in journal (Refereed)
    Abstract [en]

    Free standing and strong odor-removing composite films of cellulose nanofibrils (CNF) with a high content of nanoporous zeolite adsorbents have been colloidally processed. Thermogravimetric desorption analysis (TGA) and infrared spectroscopy combined with computational simulations showed that commercially available silicalite-1 and ZSM-5 have a high affinity and uptake of volatile odors like ethanethiol and propanethiol, also in the presence of water. The simulations showed that propanethiol has a higher affinity, up to 16%, to the two zeolites compared with ethanethiol. Highly flexible and strong free-standing zeolite CNF films with an adsorbent loading of 89 w/w% have been produced by Ca-induced gelation and vacuum filtration. The CNF-network controls the strength of the composite films and 100 mu m thick zeolite CNF films with a CNF content of less than 10 vol % displayed a tensile strength approaching 10 MPa. Headspace solid phase microextraction (SPME) coupled to gas chromatography mass spectroscopy (GC/MS) analysis showed that the CNF zeolite films can eliminate the volatile thiol-based odors to concentrations below the detection ability of the human olfactory system. Odor removing zeolite-cellulose nanofibril films could enable improved transport and storage of fruits and vegetables rich in odors, for example, onion and the tasty but foul-smelling South-East Asian Durian fruit.

  • 8. Larin, Alexander V.
    et al.
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Rybakov, Andrey A.
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Physical Chemistry.
    Carbonate "door" in the NaKA zeolite as the reason of higher CO2 uptake relative to N-22012In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 162, p. 98-104Article in journal (Refereed)
    Abstract [en]

    Theoretical calculations are performed on a model zeolite A where sodium ions have successively been exchanged with potassium. Using both isolated cluster and periodic DFT calculations, we made an attempt to explain how the chemisorbed carbonate species in the material contribute to the exceptionally high CO2 over N-2 selectivity of nearly 200 found in recent experiments [Liu et al. [1]] with the zeolite NaKA as adsorbent to capture and separate carbon dioxide from a gas mixture containing nitrogen. We have shown that the high carbonate forming at the potassium positions in the 8R windows (KII) results in a larger 8R window diameter potentially enhancing the CO2 uptake if adsorption is measured for individual gases.

  • 9. Larin, Alexander V.
    et al.
    Rybakov, Andrey A.
    Zhidomirov, Georgii M.
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Vercauteren, Daniel P.
    Oxide clusters as source of the third oxygen atom for the formation of carbonates in alkaline earth dehydrated zeolites2011In: Journal of Catalysis, ISSN 0021-9517, E-ISSN 1090-2694, Vol. 281, no 2, p. 212-221Article in journal (Refereed)
    Abstract [en]

    In our paper, we show that carbonates can be formed with almost no energetic barrier from CO(2) and metal-oxide binuclear MO(x)M species (M = Mg, Ca, Sr, Ba, with X = 1-4, depending on the cation) in alkaline earth zeolites, mordenite (MOR) and phillipsite (PHI), on the basis of quantum mechanical density functional theory (DFT) calculations at both isolated cluster and 3D periodic levels. The participation of MO(x)M species (X = 1 and 3) explains the source of the third O atom in CO(3) species in dehydrated zeolites, on the basis of a good agreement between the calculated and experimental positions of the asymmetric and symmetric CO(3) vibration bands, of the ratio of their intensities, and of the weak dependence versus the cation and framework type. The reaction of formation of dimethylcarbonate from CaCO(3)Ca in the 8-membered (8R) ring of MOR and methanol has also been considered, suggesting the carbonate activity as the source of CO(2) at elevated temperatures.

  • 10.
    Liu, Qingling
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Bacsik, Zoltan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sun, Junliang
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    NaKA sorbents with high CO2-over-N2 selectivity and high capacity to adsorb CO22010In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 46, p. 4502-4504Article in journal (Refereed)
    Abstract [en]

    The uptake of carbon dioxide and nitrogen gas by zeolite NaKA was studied. A very high ideal CO2-over-N2 selectivity and a high CO2 capacity were observed at an optimal K+ content of 17 at.%. NaKA is a very promising adsorbent for CO2 separation from water-free flue gases.

  • 11.
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Multiscale Modeling of Molecular Sieving in LTA-type Zeolites: From the Quantum Level to the Macroscopic2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    LTA-type zeolites with narrow window apertures coinciding with the approximate size of small gaseous molecules such as CO2 and N2 are interesting candidates for adsorbents with swing adsorption technologies due to their molecular sieving capabilities and otherwise attractive properties. These sieving capabilities are dependent on the energy barriers of diffusion between the zeolite pores, which can be fine-tuned by altering the framework composition. An ab initio level of theory is necessary to accurately describe specific gas-zeolite interaction and diffusion properties, while it is desirable to predict the macroscopic scale diffusion for industrial applications. Hence, a multiscale modeling approach is necessary to describe the molecular sieving phenomena exhaustively.

    In this thesis, we use several different modeling methods on different length and time scales to describe the diffusion driven uptake and separation of CO2 and N2 in Zeolite NaKA. A combination of classical force field based modeling methods are used to show the importance of taking into account both thermodynamic, as well as, kinetic effects when modeling gas uptake in narrow pore zeolites where the gas diffusion is to some extent hindered. For a more detailed investigation of the gas molecules’ pore-to-pore dynamics in the material, we present a procedure to compute the free energy barriers of diffusion using spatially constrained ab initio Molecular Dynamics. With this procedure, we seek to identify diffusion rate determining local properties of the Zeolite NaKA pores, including the Na+-to-K+ exchange at different ion sites and the presence of additional CO2 molecules in the pores. This energy barrier information is then used as input for the Kinetic Monte Carlo method, allowing us to simulate and compare these and other effects on the diffusion driven uptake using a realistic powder particle model on macroscopic timescales.

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  • 12.
    Mace, Amber
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Ecole Polytechnique Fédéralede Lausanne (EPFL), Switzerland.
    Barthel, Senja
    Smit, Berend
    Automated Multiscale Approach To Predict Self-Diffusion from a Potential Energy Field2019In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 15, no 4, p. 2127-2141Article in journal (Refereed)
    Abstract [en]

    For large-scale screening studies there is a need to estimate the diffusion of gas molecules in nanoporous materials more efficiently than (brute force) molecular dynamics. In particular for systems with low diffusion coefficients molecular dynamics can be prohibitively expensive. An alternative is to compute the hopping rates between adsorption sites using transition state theory. For large-scale screening this requires the automatic detection of the transition states between the adsorption sites along the different diffusion paths. Here an algorithm is presented that analyzes energy grids for the moving particles. It detects the energies at which diffusion paths are formed, together with their directions. This allows for easy identification of nondiffusive systems. For diffusive systems, it partitions the grid coordinates assigned to energy basins and transitions states, permitting a transition state theory based analysis of the diffusion. We test our method on CH4 diffusion in zeolites, using a standard kinetic Monte Carlo simulation based on the output of our grid analysis. We find that it is accurate, fast, and rigorous without limitations to the geometries of the diffusion tunnels or transition states.

  • 13.
    Mace, Amber
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Caretta, Martina Angela
    Stockholm University, Faculty of Social Sciences, Department of Human Geography.
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History.
    Undervisning måste få samma status som forskning2014In: Universitetsläraren, ISSN 0282-4973, no 12, p. 30-31Article in journal (Other (popular science, discussion, etc.))
  • 14.
    Mace, Amber
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Hedin, Niklas
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Role of Ion Mobility in Molecular Sieving of CO2 over N-2 with Zeolite NaKA2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 46, p. 24259-24267Article in journal (Refereed)
    Abstract [en]

    Classical molecular dynamics and Grand Canonical Monte Carlo simulations are carried out for sorbates (CO2 and N-2) in zeolite NaKA using a universal type ab initio force field. By combining the results of these simulations, we reproduce the CO2 uptake as a function of the K+ content in the zeolite NaKA as measured experimentally by Liu et al.(1) The experiment yielded an exceptionally high CO2-over-N-2 selectivity of >200 at a specific K+/(K+ + Na+) ratio of 17 atom %. This high selectivity could be attributed to the nonlinear uptake dependency of the K+/(K+ + Na+) ratio measured for both CO2 and N-2. Additionally, our simulations show a strong coupling between the self-diffusion of CO2 and the site-to-site jumping rate of the extra-framework cations. These results show that this nonlinear uptake dependency of CO2 is the result of molecular sieving. Following this, our simulations conclude that contributions must be taken into account when modeling the uptake of this and similar materials both thermodynamic and kinetic with the same functionalities.

  • 15.
    Mace, Amber
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Leetmaa, Mikael
    Uppsala universitet, Institutionen för fysik och astronomi.
    Temporal coarse graining of CO2 and N2 diffusion in Zeolite NaKA; from the quantum scale to the macroscopicManuscript (preprint) (Other academic)
    Abstract [en]

    The kinetic CO2-over-N2 sieving capabilities in narrow pore zeolite are dependent on the free energy barriers of diffusion between the zeolite pores, which can be fine-tuned by altering the framework composition. An ab initio level of theory is necessary to accurately compute the energy barriers, while it is desirable to predict the macroscopic scale diffusion for industrial applications. Using spatially constrained ab initio molecu- lar dynamics on the ps time scale, the free energy barriers of diffusion can be predicted for different local pore properties in order to identify those that are rate determining for the pore-to-pore diffusion. Specifically, we investigate the effects of the Na+-to-K+ exchange at the different cation sites and the CO2 loading. These computed energy barriers are then used as input for the Kinetic Monte Carlo method, coarse-graining the dynamic simulation steps to the pore-to-pore diffusion. With this approach we simulate how the identified rate determining properties as well as the application of skin layer surface defects affect the diffusion driven uptake in a realistic powder particle model on a macroscopic time scale. Finally, we suggest a model by combining these effects, which provides an excellent agreement with the experimental CO2 and N2 uptake behaviors presented by Liu et al.

  • 16.
    Mace, Amber
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Laasonen, Kari
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Free energy barriers for CO2 and N-2 in zeolite NaKA: an ab initio molecular dynamics approach2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, no 1, p. 166-172Article in journal (Refereed)
    Abstract [en]

    Ab initio Molecular Dynamics (AIMD) is used with spatial constraints to estimate the free energy barriers of diffusion for CO2 and N-2 gas molecules in zeolite NaA and KA. We investigate the extent to which the diffusion of these gas molecules is hindered, in the two separate cases of a smaller Na+ ion or a larger K+ ion blocking the 8-ring pore window. In contrast to classical Molecular Dynamics, AIMD performs these computations accurately and unbiased in the absence of empirical parameterization. Our work has resulted in stable and reliable force profiles. The profiles show that the larger K+ ion effectively blocks the passage of both CO2 and N-2 molecules while the smaller Na+ ion will allow both molecules to pass. These results are a quantitative demonstration of the concept of pore blocking where we compute the effect, which the size of the respective cation occupying the pore window has on diffusive properties of each gas molecule. Hence, this effect can be altered through ion exchange to fine-tune the functionality of a specific zeolite as a molecular sieve.

  • 17.
    Mace, Amber
    et al.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Leetmaa, Mikael
    Laaksonen, Aatto
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Temporal Coarse Graining of CO2 and N-2 Diffusion in Zeolite NaKA: From the Quantum Scale to the Macroscopic2015In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 11, no 10, p. 4850-4860Article in journal (Refereed)
    Abstract [en]

    The kinetic CO2-over-N-2 sieving capabilities in narrow pore zeolites are dependent on the free-energy barriers of diffusion between the zeolite pores, which can be fine-tuned by altering the framework composition. An ab initio level of theory is necessary to accurately compute the energy barriers, whereas it is desirable to predict the macroscopic scale diffusion for industrial applications. Using ab initio molecular dynamics on the picosecond time scale, the free-energy barriers of diffusion can be predicted for different local pore properties in order to identify those that are rate-determining for the pore-to-pore diffusion. Specifically, we investigate the effects of the Na+-to-K+ exchange at the different cation sites and the CO, loading in Zeolite NaKA. These computed energy barriers are then used as input for the Kinetic Monte Carlo method, coarse graining the dynamic simulation steps to the pore-to-pore diffusion. With this approach, we simulate how the identified rate-determining properties as well as the application of skin-layer surface defects affect the diffusion driven uptake in a realistic Zeolite NaKA powder particle model on a macroscopic time scale. Lastly, we suggest a model by combining these effects, which provides an excellent agreement with the experimental CO2 and N-2 uptake behaviors presented by Liu et Commun. 2010, 46, 4502-4504.

  • 18. Meyer, Benjamin
    et al.
    Barthel, Senja
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). École Polytechnique Fédérale de Lausanne (EPFL), Switzerland.
    Vannay, Laurent
    Guillot, Benoit
    Smit, Berend
    Corminboeuf, Clémence
    DORI Reveals the Influence of Noncovalent Interactions on Covalent Bonding Patterns in Molecular Crystals Under Pressure2019In: Journal of Physical Chemistry Letters, ISSN 1948-7185, E-ISSN 1948-7185, Vol. 10, no 7, p. 1482-1488Article in journal (Refereed)
    Abstract [en]

    The study of organic molecular crystals under high pressure provides fundamental insight into crystal packing distortions and reveals mechanisms of phase transitions and the crystallization of polymorphs. These solid-state transformations can be monitored directly by analyzing electron charge densities that are experimentally obtained at high pressure. However, restricting the analysis to the featureless electron density does not reveal the chemical bonding nature and the existence of intermolecular interactions. This shortcoming can be resolved by the use of the DORI (density overlap region indicator) descriptor, which is capable of simultaneously detecting both covalent patterns and noncovalent interactions from electron density and its derivatives. Using the biscarbonyt[14]annulene crystal under pressure as an example, we demonstrate how DORI can be exploited on experimental electron densities to reveal and monitor changes in electronic structure patterns resulting from molecular compression. A novel approach based on a flood-fill-type algorithm is proposed for analyzing the topology of the DORI isosurface. This approach avoids the arbitrary selection of DORI isovalues and provides an intuitive way to assess how compression packing affects covalent bonding in organic solids.

  • 19.
    Wikfeldt, Kjartan Thor
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Leetmaa, Mikael
    Stockholm University, Faculty of Science, Department of Physics.
    Mace, Amber
    Stockholm University, Faculty of Science, Department of Physics.
    Nilsson, Anders
    Stockholm University, Faculty of Science, Department of Physics.
    Pettersson, Lars G. M.
    Stockholm University, Faculty of Science, Department of Physics.
    Oxygen-oxygen correlations in liquid water: Addressing the discrepancy between diffraction and EXAFS using a novel multiple –data set fitting technique2010In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 132, no 10, article id 104513Article in journal (Refereed)
    Abstract [en]

    The first peak of the oxygen-oxygen pair-correlation function (O-O PCF) is a critical measure of the first coordination shell distances in liquid water. Recently, a discrepancy has been uncovered between diffraction and extended x-ray absorption fine-structure (EXAFS) regarding the height and position of this peak, where EXAFS gives a considerably more well-defined peak at a shorter distance compared with diffraction results. This discrepancy is here investigated through a new multiple data set structure modeling technique, SpecSwap-RMC, based on the reverse Monte Carlo (RMC) method. Fitting simultaneously to both EXAFS and a diffraction-based O-O PCF shows that, even though the reported EXAFS results disagree with diffraction, the two techniques can be reconciled by taking into account a strong contribution from the focusing effect originating from nearly linear hydrogen bonds. This many-body contribution, which is usually neglected in RMC modeling of EXAFS data, is included in the fits by precomputing and storing EXAFS signals from real-space multiple-scattering calculations on a large number of unique water clusters. On the other hand, fitting also the O-O PCF from diffraction is seen to enhance the amount of structural disorder in the joint fit. Thus, both nearly linear hydrogen bonds and local structural disorder are important to reproduce diffraction and EXAFS simultaneously. This work also illustrates a few of many possible uses of the SpecSwap-RMC method in modeling disordered materials, particularly for fitting computationally demanding techniques and combining multiple data sets.

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