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- Li, Yunxiang, et al.
(författare)
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Microporous pure-silica IZM-2
- 2017
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 237, s. 222-227
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Tidskriftsartikel (refereegranskat)abstract
- Pure-silica IZM-2 was synthesized for the first time, and the concentration of sodium hydroxide used during synthesis affected the phase purity and size of crystals. Most of the micropores in calcined pure silica IZM-2 that was synthesized in the presence of high concentrations of sodium hydroxide were inaccessible to N-2 adsorption; however, the micropores could be rendered accessible by applying either of two different post-synthetic treatments. Pure-silica IZM-2 could also be synthesized without sodium ions using the hydroxide version of the template. In this case, the micropores were accessible to N-2 directly after calcination. The size of pure-silica IZM-2 crystals obtained increased with the concentration of sodium hydroxide, with the highest concentrations giving spherical and micrometer-sized aggregates of pure-silica IZM-2 that consisted of intergrown particles (60-500 nm). The nature of the defects in pure-silica IZM-2 was studied with a combination of H-1, and Si-29 solid-state NMR spectroscopy. As expected, direct-polarization Si-29 NMR spectroscopy showed that the number of non-condensed silica groups decreased upon calcination. Calcined samples also showed broader Si-29 NMR bands for the fully condensed silica moieties, which indicated a broader distribution of bond angles and/or bond lengths. The siloxy and silanol groups in calcined pure-silica IZM-2 were accessible to protonation as determined by H-1 NMR spectroscopy. We could not determine the structure of pure-silica IZM-2 in its aggregated form; however, further studies of the synthetic conditions could yield larger, non-aggregated crystals that would facilitate structural determination.
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| 2. |
- Li, Yunxiang, 1986-
(författare)
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Modification of zeolites and synthesis of SAPO-templated carbon
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Zeolites are crystalline aluminosilicates with diverse structures and uniform porosities. They are widely used as catalysts, adsorbents and ion-exchangers in industry. Direct or post modifications optimize the performance of zeolites for different applications. In this thesis, IZM-2 and TON-type zeolites were synthesized, modified and studied. In addition, FAU-type zeolite and silicoaluminophosphate (SAPO) molecular sieves were applied as templates for the preparation of microporous carbons.In the first part of this thesis, the IZM-2 zeolite with an unknown structure was synthesized. We focused on the increasing the secondary porosity and the varied framework compositions upon post modifications.The structure determination of this IZM-2 zeolite was hindered by the small size of crystals. In the second part of this thesis, the synthesis composition was directly modified in order to increase the crystal sizes. IZM-2 crystals were enlarged by excluding the aluminium atoms from the framework. The micropores of the obtained pure-silica polymorphs were activated by ion-exchanging alkali-metal ions with protons.Typically, TON-type zeolites that are synthesized at hydrothermal conditions under stirring have needle-shaped crystals. In the third part of this thesis, snowflake-shaped aggregates were produced by using static hydrothermal conditions for the synthesis of TON-type zeolites. The effects of synthesis parameters on the growth and morphology of crystals were discussed in detail.In the last part of this thesis, microporous carbons with a structural regularity were prepared by chemical vapour deposition (CVD) of propylene using a silicoaluminophosphate (SAPO-37) template. Compared to the conventional zeolite templates, the SAPO template could be removed under mild conditions, without using hydrofluoric acid, and the generated carbons had a large specific surface area and a high fraction of ultrasmall micropores.
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| 3. |
- Xu, Chao, et al.
(författare)
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Porous Polymers and Porous Carbons for CO2 Capture and VOC Removal
- 2017
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Konferensbidrag (refereegranskat)abstract
- Porous materials have potential applications in gas capture and storage and heterogeneous catalysis.1 We have developed a series of porous polymers (PPs) and porous carbons (PCs) with high surface areas and tunable pore sizes. They were studied as potential sorbents for CO2 separation and volatile organic compounds (VOCs) removal.2 The PPs were synthesized by Schiff base polycondensations. The sustainable PCs were synthesized from natural abundant celluloses by a physical carbonization/ activation process. All the PPs and PCs had ultramicropores and displayed relatively high CO2 uptakes (0.93-2.29 mmol/g at 0.15 bar, 2.20-5.52 mmol/g at 1 bar; 273 K) and CO2-over-N2 selectivities (31-90 for CO2/N2 mixtures with 15 vol%/85 vol% at 273 K). In addition, the ACs displayed remarkable adsorption capacity for vapors of VOCs with values up to 0.97 mmol/g at very low VOC concentrations (200 ppmv) and with ultrahigh VOC-over-N2 selectivity (9.35 × 103 at 293 K for 0.02 vol%/99.8 vol% of benzene/N2 mixture). The diverse synthesis routes and rich functionalities of PPs allowed further post-modification to improve their performance in CO2 capture. The PPs modified by alkyl amines induced chemisorption of CO2, which was confirmed by the study of in situ infrared (IR) and solid-state 13C NMR spectroscopy. As a result, the amine-modified PPs had a large CO2 capacity and very high CO2-over-N2 selectivity at the CO2 concentrations relevant for post-combustion capture of CO2.
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