Use of the PIXEL method to investigate gas adsorption in metal–organic frameworks

PIXEL has been used to perform calculations of adsorbate-adsorbent interaction energies between a range of metal–organic frameworks (MOFs) and simple guest molecules. Interactions have been calculated for adsorption between MOF-5 and Ar, H(2), and N(2); Zn(2)(BDC)(2)(TED) (BDC = 1,4-benzenedicarboxylic acid, TED = triethylenediamine) and H(2); and HKUST-1 and CO(2). The locations of the adsorption sites and the calculated energies, which show differences in the Coulombic or dispersion characteristic of the interaction, compare favourably to experimental data and literature energy values calculated using density functional theory

Bronstedova kyselost v zeolitech meřená pomocí deprotonační energie

Acid forms of zeolites have been used in industry for several decades but scaling the strength of their acid centers is still an unresolved and intensely debated issue. In this paper, the Bronsted acidity strength in aluminosilicates measured by their deprotonation energy (DPE) was investigated for FAU, CHA, IFR, MOR, FER, MFI, and TON zeolites by means of periodic and cluster calculations at the density functional theory (DFT) level. The main drawback of the periodic DFT is that it does not provide reliable absolute values due to spurious errors associated with the background charge introduced in anion energy calculations. To alleviate this problem, we employed a novel approach to cluster generation to obtain accurate values of DPE. The cluster models up to 150 T atoms for the most stable Bronsted acid sites were constructed on spheres of increasing diameter as an extension of Harrison's approach to calculating Madelung constants. The averaging of DPE for clusters generated this way provides a robust estimate of DPE for investigated zeolites despite slow convergence with the cluster size. The accuracy of the cluster approach was further improved by a scaled electrostatic embedding scheme proposed in this work. The electrostatic embedding model yields the most reliable values with the average deprotonation energy of about 1245 +/- 9 kJ center dot mol(-1) for investigated acidic zeolites. The cluster calculations strongly indicate a correlation between the deprotonation energy and the zeolite framework density. The DPE results obtained with our electrostatic embedding model are highly consistent with the previously reported QM/MM and periodic calculations.Síla Bronstedovy kyselosti v aluminosilikátech byla měřena pomocí jejich deprotonační energie a DFT výpočtů. Zkoumány byly materiály na bázi FAU, CHA, IFR, MOR, FER, MFI a TON zeolitů. DFT výpočty indikují korelaci mezi deprotonační energií a hustotou zeolitické struktury

Přehodnocení interpretace CO adsorbovaného na Lewisových kyselých polohách v MOR zeolitech s alkalickými kovy

The interaction of CO with alkali metal-exchanged mordenite has been investigated by means of IR spectroscopy and calorimetry along with theoretical calculations based on DFT corrected to coupled-cluster accuracy (DFT/CC). It has been convincingly shown that Li+ is at least partially exchanged into the constricted part of the MOR structure as manifested by the low-frequency band at 2181 cm−1 and the isosteric heat of 44 kJ/mol. In the case of Na-MOR samples, significant changes have been observed in the stabilities of high- (2177 cm−1) and low-frequency (2165 cm−1) bands upon CO desorption, with the change of the Si/Al ratio from 40 to 9. Based on the kinetic measurements, it can be concluded that a crucial role in the MOR material is played by diffusion limitations, which are significantly influenced by the Si/Al ratio and the size of the cations. Similar effects also result in the increased stability of the 2138 cm−1 band of Na/K-MOR samples with higher Al content, where the “gate” effect is observed upon N2 adsorption. The dual cationic sites are directly observed only for the K-MOR sample via the weak band around 2150 cm−1. The formation of dual cationic sites cannot be completely ruled out in the case of Na-MOR, but their presence is most likely hidden in the low-frequency band.Interakce CO s mordenity s ionty alkalických kovů byly studovány pomocí IR spektroskopie a kalorimetrie. Výsledky byly porovnány s teoretickými výpočty na bázi DFT/CC

Characterizing the dark state in thymine and uracil by double resonant spectroscopy and quantum computation.

We report on gas phase double resonant spectroscopy of both the ground state and the dark excited state in isolated uracil and thymine. We also report lifetimes of the dark state for different excitation wavelengths. In combination with ab initio calculations the results suggest that the dark state is of triplet ((3)ππ*) character

Carbonylation of Methanol on Metal Acid Zeolites: Evidence for a Mechanism Involving a Multisite Active Center

Blasco Lanzuela, T.; Boronat Zaragoza, M.; Concepción Heydorn, P.; Corma Canós, A.; Law, D.; Vidal Moya, JA. (2007). Carbonylation of Methanol on Metal Acid Zeolites: Evidence for a Mechanism Involving a Multisite Active Center. Angewandte Chemie International Edition. 46(21):3938-3941. https://doi.org/10.1002/anie.200700029S393839414621in New Syntheses with Carbon Monoxide, (Ed.: ), Springer, Berlin, 1980, pp. 372–413.Sunley, G. J., & Watson, D. J. (2000). High productivity methanol carbonylation catalysis using iridium. Catalysis Today, 58(4), 293-307. doi:10.1016/s0920-5861(00)00263-7Stepanov, A. G., Luzgin, M. V., Romannikov, V. N., & Zamaraev, K. I. (1995). NMR Observation of the Koch Reaction in Zeolite H-ZSM-5 under Mild Conditions. Journal of the American Chemical Society, 117(12), 3615-3616. doi:10.1021/ja00117a032Fujimoto, K., Shikada, T., Omata, K., & Tominaga, H. (1984). VAPOR PHASE CARBONYLATION OF METHANOL WITH SOLID ACID CATALYSTS. Chemistry Letters, 13(12), 2047-2050. doi:10.1246/cl.1984.2047Xu, Q., Inoue, S., Tsumori, N., Mori, H., Kameda, M., Tanaka, M., … Souma, Y. (2001). Carbonylation of tert -butyl alcohol over H-zeolites. Journal of Molecular Catalysis A: Chemical, 170(1-2), 147-153. doi:10.1016/s1381-1169(01)00054-1Ellis, B., Howard, M. J., Joyner, R. W., Reddy, K. N., Padley, M. B., & Smith, W. J. (1996). Heterogeneous catalysts for the direct, halide-free carbonylation of methanol. Studies in Surface Science and Catalysis, 771-779. doi:10.1016/s0167-2991(96)80288-6Stepanov, A. G., Luzgin, M. V., Romannikov, V. N., Sidelnikov, V. N., & Zamaraev, K. I. (1996). Formation of Carboxylic Acids from Alcohols and Olefins in Zeolite H-ZSM-5 under Mild Conditions via Trapping of Alkyl Carbenium Ions with Carbon Monoxide: Anin Situ13C Solid State NMR Study. Journal of Catalysis, 164(2), 411-421. doi:10.1006/jcat.1996.0397Clingenpeel, T. H., Wessel, T. E., & Biaglow, A. I. (1997). 13C NMR Study of the Carbonylation of Benzene with CO in Sulfated Zirconia. Journal of the American Chemical Society, 119(23), 5469-5470. doi:10.1021/ja970824pLuzgin, M. V., Romannikov, V. N., Stepanov, A. G., & Zamaraev, K. I. (1996). Interaction of Olefins with Carbon Monoxide on Zeolite H-ZSM-5. NMR Observation of the Friedel−Crafts Acylation of Alkenes at Ambient Temperature. Journal of the American Chemical Society, 118(44), 10890-10891. doi:10.1021/ja9615381Cheung, P., Bhan, A., Sunley, G. J., & Iglesia, E. (2006). Selective Carbonylation of Dimethyl Ether to Methyl Acetate Catalyzed by Acidic Zeolites. Angewandte Chemie, 118(10), 1647-1650. doi:10.1002/ange.200503898Cheung, P., Bhan, A., Sunley, G. J., & Iglesia, E. (2006). Selective Carbonylation of Dimethyl Ether to Methyl Acetate Catalyzed by Acidic Zeolites. Angewandte Chemie International Edition, 45(10), 1617-1620. doi:10.1002/anie.200503898Jiang, Y., Hunger, M., & Wang, W. (2006). On the Reactivity of Surface Methoxy Species in Acidic Zeolites. Journal of the American Chemical Society, 128(35), 11679-11692. doi:10.1021/ja061018ySpoto, G., Zecchina, A., Bordiga, S., Ricchiardi, G., Martra, G., Leofanti, G., & Petrini, G. (1994). Cu(I)-ZSM-5 zeolites prepared by reaction of H-ZSM-5 with gaseous CuCl: Spectroscopic characterization and reactivity towards carbon monoxide and nitric oxide. Applied Catalysis B: Environmental, 3(2-3), 151-172. doi:10.1016/0926-3373(93)e0032-7Bludský, O., Nachtigall, P., Čičmanec, P., Knotek, P., & Bulánek, R. (2005). Characterization of the Cu+ sites in MFI zeolites: combined computational and experimental study. Catalysis Today, 100(3-4), 385-389. doi:10.1016/j.cattod.2004.09.070Campbell, S. M., Jiang, X.-Z., & Howe, R. F. (1999). Methanol to hydrocarbons: spectroscopic studies and the significance of extra-framework aluminium. Microporous and Mesoporous Materials, 29(1-2), 91-108. doi:10.1016/s1387-1811(98)00323-0KUBELKOVA, L. (1990). Reactivity of surface species on zeolites in methanol conversion. Journal of Catalysis, 124(2), 441-450. doi:10.1016/0021-9517(90)90191-lLazo, N. D., Murray, D. K., Kieke, M. L., & Haw, J. F. (1992). In situ carbon-13 solid-state NMR study of the Cu/ZnO/Al2O3 methanol synthesis catalyst. Journal of the American Chemical Society, 114(22), 8552-8559. doi:10.1021/ja00048a03

Experimentální a teoretická studie adsorpce propenu na iontově vyměněné FER zeolity

Propene adsorption on Li- and Na-FER zeolites was investigated combining IR spectroscopy and calorimetric measurements of adsorption heats with DFT calculations using a DFT/CC scheme based on the PBE density functional. Considering the good agreement between experimental and theoretical results, the following adsorption complexes of propene in the M-FER zeolites investigated in this study can be distinguished: (i) propene interacting with the zeolitic framework via dispersion interactions mainly populated in zeolites with a high Si/Al ratio and with a characteristic nu(C=C) vibrational band at 1646 cm(-1) and adsorption heat of approximately 48 kJ/mol, (ii) propene interacting with cations coordinated in 6-rings characterized by IR bands at 1637 cm(-1) (Li-FER) and 1636 cm(-1) (Na-FER), (iii) propene adsorbed on remaining cationic positions excluding cationic positions in 6-rings characterized by IR bands at 1630 cm(-1) (Li-FER) and 1633 cm(-1) (Na-FER) and (iv) propene bridging two nearby sodium cations in dual-cation sites characterized by a vibrational band at 1626 cm(-1) and with an adsorption heat of 85 kJ/mol, which is 6 kJ/mol higher than that of the strongest interaction with a single Na+ cation (79 kJ/mol). The population of bridged complexes in Na-FER was significantly lower than those in previously studied K-FER zeolites due to the preference of potassium cations for 8-rings, which is more suitable for the creation of dual-cation sites than 6-rings, wherein sodium cations are preferentially coordinated. No bridged complexes were found in the case of Li-FER because Li+ cations are closer to the framework oxygen atoms and thus relatively long distance from each other.Adsorpce propenu na Li- a Na-FER byla studována kombinací IR spektroskopie a kalorimetrického měření adsorpčního tepla spolu s DFT výpočty za využití DFT/CC schématu založeného na PBE funkcionálu hustoty. Dobrý soulad byl nalezen mezi experimentálními a teoretickými výsledky