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Hidetoshi Kita - One of the best experts on this subject based on the ideXlab platform.
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preparation of cha zeolite Chabazite crystals and membranes without organic structural directing agents for co2 separation
Journal of Membrane Science, 2019Co-Authors: Bo Liu, Rongfei Zhou, Katsunori Yogo, Hidetoshi KitaAbstract:Abstract CHA zeolite (Chabazite) crystals and membranes were prepared from organic structural directing agents-free (OSDA-free) gels. Chabazite membranes were grown on the tubular alumina supports. The effect of cesium and fluoride salts on the crystallization of Chabazite crystals and membranes were investigated. Highly crystalline Chabazite and uniform Chabazite membranes were only obtained from the gel containing the cesium and fluoride salts. Single CO2, N2 and CH4 permeances and mixed gas separations in CO2/N2 and CO2/CH4 binary mixtures through Chabazite membranes were measured. Temperature and pressure affected the permeances and separation selectivities in two mixtures. The best membrane showed CO2/N2 and CO2/CH4 separation selectivities as high as 16 and 46 together with CO2 permeances of ~ 1.0 × 10-7 mol/(m2 s Pa) at a high temperature of 473 K in equimolar dry CO2/N2 and CO2/CH4 binary mixtures, respectively. The CO2/N2 and CO2/CH4 selectivities lost only 11% and 15%, and CO2 permeances lost only 18% and 20% in equimolar wet CO2/N2 and CO2/CH4 mixtures (8% in mole of water vapor) at 473 K compared to these values in dry mixtures, respectively. The OSDA-free Chabazite membranes were hydrothermally stable in the presence of vapor water for 4 d at 378 K.
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synthesis of low silica cha zeolite Chabazite in fluoride media without organic structural directing agents and zeolites
Microporous and Mesoporous Materials, 2014Co-Authors: Bo Liu, Rongfei Zhou, Yihong Zheng, Tian Gui, Fei Zhang, Xiangshu Chen, Hidetoshi KitaAbstract:Abstract The fluoride route was adopted for the preparation of Chabazite (Si/Al = 2.5–3.5) in the absence of organic structural directing agents (OSDAs). The crystallization kinetics of the fluoride-derived Chabazite and the effects of gel SiO 2 /Al 2 O 3 ratio, gel F − /SiO 2 ratio, fluoride source and synthesis temperature on the morphology and composition of crystals were investigated. A certain amount of the specific fluoride source (NH 4 F) dominated the crystallization of CHA phase in the competitive growth of MER/CHA phases. The fluoride-derived Chabazite by in situ synthesis had a particle size of 15–20 μm. Seeded-in-gel synthesis increased the crystallization rate and resulted in the smaller crystals with higher BET surface area and microspore volume. The location of fluoride ion in zeolite framework and the role of fluoride salts on Chabazite crystallization were also demonstrated.
Bo Liu - One of the best experts on this subject based on the ideXlab platform.
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preparation of cha zeolite Chabazite crystals and membranes without organic structural directing agents for co2 separation
Journal of Membrane Science, 2019Co-Authors: Bo Liu, Rongfei Zhou, Katsunori Yogo, Hidetoshi KitaAbstract:Abstract CHA zeolite (Chabazite) crystals and membranes were prepared from organic structural directing agents-free (OSDA-free) gels. Chabazite membranes were grown on the tubular alumina supports. The effect of cesium and fluoride salts on the crystallization of Chabazite crystals and membranes were investigated. Highly crystalline Chabazite and uniform Chabazite membranes were only obtained from the gel containing the cesium and fluoride salts. Single CO2, N2 and CH4 permeances and mixed gas separations in CO2/N2 and CO2/CH4 binary mixtures through Chabazite membranes were measured. Temperature and pressure affected the permeances and separation selectivities in two mixtures. The best membrane showed CO2/N2 and CO2/CH4 separation selectivities as high as 16 and 46 together with CO2 permeances of ~ 1.0 × 10-7 mol/(m2 s Pa) at a high temperature of 473 K in equimolar dry CO2/N2 and CO2/CH4 binary mixtures, respectively. The CO2/N2 and CO2/CH4 selectivities lost only 11% and 15%, and CO2 permeances lost only 18% and 20% in equimolar wet CO2/N2 and CO2/CH4 mixtures (8% in mole of water vapor) at 473 K compared to these values in dry mixtures, respectively. The OSDA-free Chabazite membranes were hydrothermally stable in the presence of vapor water for 4 d at 378 K.
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synthesis of low silica cha zeolite Chabazite in fluoride media without organic structural directing agents and zeolites
Microporous and Mesoporous Materials, 2014Co-Authors: Bo Liu, Rongfei Zhou, Yihong Zheng, Tian Gui, Fei Zhang, Xiangshu Chen, Hidetoshi KitaAbstract:Abstract The fluoride route was adopted for the preparation of Chabazite (Si/Al = 2.5–3.5) in the absence of organic structural directing agents (OSDAs). The crystallization kinetics of the fluoride-derived Chabazite and the effects of gel SiO 2 /Al 2 O 3 ratio, gel F − /SiO 2 ratio, fluoride source and synthesis temperature on the morphology and composition of crystals were investigated. A certain amount of the specific fluoride source (NH 4 F) dominated the crystallization of CHA phase in the competitive growth of MER/CHA phases. The fluoride-derived Chabazite by in situ synthesis had a particle size of 15–20 μm. Seeded-in-gel synthesis increased the crystallization rate and resulted in the smaller crystals with higher BET surface area and microspore volume. The location of fluoride ion in zeolite framework and the role of fluoride salts on Chabazite crystallization were also demonstrated.
Jürgen Hafner - One of the best experts on this subject based on the ideXlab platform.
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Structure and properties of metal-exchanged zeolites studied using gradient-corrected and hybrid functionals. I. Structure and energetics.
Journal of Chemical Physics, 2012Co-Authors: Florian Goltl, Jürgen HafnerAbstract:The structural and energetic properties of purely siliceous, proton-, and Cu- and Co-exchanged Chabazite have been studied using periodic density-functional (DFT) calculations with both conventional gradient-corrected exchange-correlation functionals and hybrid functionals mixing exact (i.e., Hartree-Fock) and DFT exchange. Spin-polarized and fixed-moment calculations have been performed to determine the equilibrium and excited spin-configurations of the metal-exchanged Chabazites. For the purely siliceous Chabazite, hybrid functionals predict a slightly more accurate cell volume and lattice geometry. For isolated Al/Si substitution sites, gradient-corrected functionals predict that the lattice distortion induced by the substitution preserves the local tetrahedral symmetry, whereas hybrid functionals lead to a distorted Al coordination with two short and two long Al-O bonds. Hybrid functionals yield a stronger cation-framework binding that conventional functionals in metal-exchanged zeolites, they favor shorter cation-oxygen bonds and eventually also a higher coordination of the cation. Both types of functionals predict the same spin in the ground-state. The structural optimization of the excited spin-states shows that the formation of a high-spin configuration leads to a strong lattice relaxation and a weaker cation-framework bonding. For both Cu- and Co-exchanged Chabazite, the prediction of a preferred location of the cation in a six-membered ring of the zeolite agrees with experiment, but the energy differences between possible cation locations and the lattice distortion induced by the Al/Si substitution and the bonding of the cation depends quite significantly on the choice of the functional. All functionals predict similar energy differences for excited spin states. Spin-excitations are shown to be accompanied by significant changes in the cation coordination, which are more pronounced with hybrid functionals. The consequences of electronic spectra and chemical reactivity are analyzed in the following papers.
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structure and properties of metal exchanged zeolites studied using gradient corrected and hybrid functionals i structure and energetics
Journal of Chemical Physics, 2012Co-Authors: Florian Goltl, Jürgen HafnerAbstract:The structural and energetic properties of purely siliceous, proton-, and Cu- and Co-exchanged Chabazite have been studied using periodic density-functional (DFT) calculations with both conventional gradient-corrected exchange-correlation functionals and hybrid functionals mixing exact (i.e., Hartree-Fock) and DFT exchange. Spin-polarized and fixed-moment calculations have been performed to determine the equilibrium and excited spin-configurations of the metal-exchanged Chabazites. For the purely siliceous Chabazite, hybrid functionals predict a slightly more accurate cell volume and lattice geometry. For isolated Al/Si substitution sites, gradient-corrected functionals predict that the lattice distortion induced by the substitution preserves the local tetrahedral symmetry, whereas hybrid functionals lead to a distorted Al coordination with two short and two long Al-O bonds. Hybrid functionals yield a stronger cation-framework binding that conventional functionals in metal-exchanged zeolites, they favor shorter cation-oxygen bonds and eventually also a higher coordination of the cation. Both types of functionals predict the same spin in the ground-state. The structural optimization of the excited spin-states shows that the formation of a high-spin configuration leads to a strong lattice relaxation and a weaker cation-framework bonding. For both Cu- and Co-exchanged Chabazite, the prediction of a preferred location of the cation in a six-membered ring of the zeolite agrees with experiment, but the energy differences between possible cation locations and the lattice distortion induced by the Al/Si substitution and the bonding of the cation depends quite significantly on the choice of the functional. All functionals predict similar energy differences for excited spin states. Spin-excitations are shown to be accompanied by significant changes in the cation coordination, which are more pronounced with hybrid functionals. The consequences of electronic spectra and chemical reactivity are analyzed in the following papers. © 2012 American Institute of Physics. [doi:10.1063/1.3676408]
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structure and properties of metal exchanged zeolites studied using gradient corrected and hybrid functionals iii energetics and vibrational spectroscopy of adsorbates
Journal of Chemical Physics, 2012Co-Authors: Florian Goltl, Jürgen HafnerAbstract:The influence of the exchange-correlation functional (semilocal gradient corrected or hybrid functional) on density-functional studies of the adsorption of CO and NO in Cu- and Co-exchanged Chabazite has been investigated, extending the studies of the structural and electronic properties of these materials [F. Goltl and J. Hafner, J. Chem. Phys. 136, 064501 (2012)10.1063/1.3676408; F. Goltl and J. Hafner, J. Chem. Phys. 136, 064502 (2012)10.1063/1.3676409] and including for comparison carbonyls and nitrosyls of Cu and Co. Hybrid functionals predict much lower adsorption energies than conventional semilocal functionals, in better agreement with experiment as far as data are available for comparison. The calculated adsorption energies show a strong linear correlation with the stability of the cation sites. For Cu(I)-Chabazite the calculated adsorption energies span almost the interval between the adsorption energies calculated for pure neutral and positively charged Cu-carbonyls and nitrosyls. For divalent ...
Karl Petter Lillerud - One of the best experts on this subject based on the ideXlab platform.
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preparation of high silica Chabazite with controllable particle size
Microporous and Mesoporous Materials, 2014Co-Authors: Zebastian Bohstrom, Bjornar Arstad, Karl Petter LillerudAbstract:Abstract In this work synthesis procedures for controlling particle size distributions of high silica Chabazite (Si/Al = 100) zeolites between 0.3 and 4.5 μm is described. The chabzite zeolite crystallization and crystal growth have been monitored using XRD, SEM and DLS. Hydrothermal treatment parameters such as time, temperature and agitation and gel composition parameters such as amounts of water and structure directing agent (SDA) have been correlated with Chabazite zeolite crystal size, crystal shape, synthesis yield and crystallinity. From this data a Chabazite zeolite formation and crystal growth mechanism based on experimental studies and previous studies has been proposed. It was also found that large aggregates formed in the Chabazite zeolite gel before any hydrothermal treatment (1 μm large when using zeolite gel with composition 1Al2O3:100SiO2:60TMAdaOH:3100H2O). The size controlling parameter and size controlling synthesis step of the Chabazite zeolite (below 1 μm) has been identified as the primary fractal aggregation of the silicium/aluminium/SDA species.
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Liquid hydrogen in protonic Chabazite
Journal of the American Chemical Society, 2005Co-Authors: Adriano Zecchina, Claudio Lamberti, Morten Bjørgen, Jenny G. Vitillo, Silvia Bordiga, G. Ricchiardi, Giuseppe Spoto, Karl Petter LillerudAbstract:Due to its fully reversible nature, H(2) storage by molecular adsorption could represent an advantage with respect to dissociative processes, where kinetic effects during the charging and discharging processes are present. A drawback of this strategy is represented by the extremely weak interactions that require low temperature and high pressure. High surface area materials hosting polarizing sites can represent a viable way toward more favorable working conditions. Of these, in this contribution, we have studied hydrogen adsorption in a series of zeolites using volumetric techniques and infrared spectroscopy at 15 K. We have found that in H-SSZ-13 zeolite the cooperative role played by high surface area, internal wall topology, and presence of high binding energy sites (protons) allows hydrogen to densify inside the nanopores at favorable temperature and pressure conditions.
Rongfei Zhou - One of the best experts on this subject based on the ideXlab platform.
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preparation of cha zeolite Chabazite crystals and membranes without organic structural directing agents for co2 separation
Journal of Membrane Science, 2019Co-Authors: Bo Liu, Rongfei Zhou, Katsunori Yogo, Hidetoshi KitaAbstract:Abstract CHA zeolite (Chabazite) crystals and membranes were prepared from organic structural directing agents-free (OSDA-free) gels. Chabazite membranes were grown on the tubular alumina supports. The effect of cesium and fluoride salts on the crystallization of Chabazite crystals and membranes were investigated. Highly crystalline Chabazite and uniform Chabazite membranes were only obtained from the gel containing the cesium and fluoride salts. Single CO2, N2 and CH4 permeances and mixed gas separations in CO2/N2 and CO2/CH4 binary mixtures through Chabazite membranes were measured. Temperature and pressure affected the permeances and separation selectivities in two mixtures. The best membrane showed CO2/N2 and CO2/CH4 separation selectivities as high as 16 and 46 together with CO2 permeances of ~ 1.0 × 10-7 mol/(m2 s Pa) at a high temperature of 473 K in equimolar dry CO2/N2 and CO2/CH4 binary mixtures, respectively. The CO2/N2 and CO2/CH4 selectivities lost only 11% and 15%, and CO2 permeances lost only 18% and 20% in equimolar wet CO2/N2 and CO2/CH4 mixtures (8% in mole of water vapor) at 473 K compared to these values in dry mixtures, respectively. The OSDA-free Chabazite membranes were hydrothermally stable in the presence of vapor water for 4 d at 378 K.
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synthesis of low silica cha zeolite Chabazite in fluoride media without organic structural directing agents and zeolites
Microporous and Mesoporous Materials, 2014Co-Authors: Bo Liu, Rongfei Zhou, Yihong Zheng, Tian Gui, Fei Zhang, Xiangshu Chen, Hidetoshi KitaAbstract:Abstract The fluoride route was adopted for the preparation of Chabazite (Si/Al = 2.5–3.5) in the absence of organic structural directing agents (OSDAs). The crystallization kinetics of the fluoride-derived Chabazite and the effects of gel SiO 2 /Al 2 O 3 ratio, gel F − /SiO 2 ratio, fluoride source and synthesis temperature on the morphology and composition of crystals were investigated. A certain amount of the specific fluoride source (NH 4 F) dominated the crystallization of CHA phase in the competitive growth of MER/CHA phases. The fluoride-derived Chabazite by in situ synthesis had a particle size of 15–20 μm. Seeded-in-gel synthesis increased the crystallization rate and resulted in the smaller crystals with higher BET surface area and microspore volume. The location of fluoride ion in zeolite framework and the role of fluoride salts on Chabazite crystallization were also demonstrated.