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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Cao, Qing, et al.
(författare)
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On the predictability of daily rainfall during rainy season over the Huaihe River Basin
- 2019
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Ingår i: Water. - : MDPI AG. - 2073-4441. ; 11:5
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Tidskriftsartikel (refereegranskat)abstract
- In terms of climate change and precipitation, there is large interest in how large-scale climatic features affect regional rainfall amount and rainfall occurrence. Large-scale climate elements need to be downscaled to the regional level for hydrologic applications. Here, a new Nonhomogeneous Hidden Markov Model (NHMM) called the Bayesian-NHMM is presented for downscaling and predicting of multisite daily rainfall during rainy season over the Huaihe River Basin (HRB). The Bayesian-NHMM provides a Bayesian method for parameters estimation. The model avoids the risk to have no solutions for parameter estimation, which often occurs in the traditional NHMM that uses point estimates of parameters. The Bayesian-NHMM accurately captures seasonality and interannual variability of rainfall amount and wet days during the rainy season. The model establishes a link between large-scale meteorological characteristics and local precipitation patterns. It also provides a more stable and efficient method to estimate parameters in the model. These results suggest that prediction of daily precipitation could be improved by the suggested new Bayesian-NHMM method, which can be helpful for water resources management and research on climate change.
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| 3. |
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| 4. |
- Li, Yunxiang, et al.
(författare)
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De-agglomeration of IZM-2 zeolite crystals by post-synthetic treatment
- 2016
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 225, s. 185-191
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Tidskriftsartikel (refereegranskat)abstract
- Highly intergrown nanocrystals are commonly observed in zeolite samples, and the densely packed agglomerates may result in small secondary porosity, which restricts the advantage of hierarchical structures. In this work we take IZM-2 zeolite as an example to demonstrate a post-treatment method with diluted hydrofluoric acid solution, which de-agglomerates intergrown zeolite nanocrystals and improves the secondary porosity. The treated samples preserve high crystallinity, similar framework composition and distinctively higher external surface area compared to the agglomerated ones. The results show that this treatment is an effective method for de-agglomeration of intergrown nanocrystals without affecting the original framework.
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| 5. |
- 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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| 6. |
- Li, Yunxiang, et al.
(författare)
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Nanocrystalline TON-type zeolites synthesized under static conditions
- 2018
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811 .- 1873-3093. ; 256, s. 84-90
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Tidskriftsartikel (refereegranskat)abstract
- Pure-phase zeolites of the TON-type were synthesized under static hydrothermal conditions, which previously have, typically, required stirring during synthesis. Heterocyclic structure directing agents (SDAs) were observed to play important roles in both the selection of the polymorphs as well as in affecting the morphology of the particles formed. When an imidazole-based SDA was used snowflake shaped particles formed, which indicated a dendritic growth pattern of the zeolite. These zeolite particles possessed intercrystalline mesopores. To the best of our knowledge, it is for the first time that snowflake-shaped particles have been observed for TON-type zeolites. Other synthesis parameters were optimized to obtain crystals with short c-axes. The c-axis shortened with an increased solid concentration used during synthesis. This shortening was attributed to both the degree of supersaturation, and a change of the crystal growth mechanism. Short c-axes could increase the concentration of pore mouths in TON-type zeolites. Altogether, synthesis of nanocrystalline zeolites of the TON type under static condition could, potentially, be advantageous to large-scale production.
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| 7. |
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| 8. |
- Verho, Oscar, et al.
(författare)
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Mesoporous silica nanoparticles applied as a support for Pd and Au nanocatalysts in cycloisomerization reactions
- 2014
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Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 2:11, s. 113316-
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Tidskriftsartikel (refereegranskat)abstract
- Ultra-small mesoporous silica nanoparticles (MSNs) have been synthesized at room temperature with particle sizes ranging from 28 to 45 nm. These MSNs have been employed as heterogeneous supports for palladium and gold nanocatalysts. The colloidal nature of the MSNs is highly useful for catalytic applications as it allows for better mass transfer properties and a more uniform distribution of the nanocatalysts in solution. The two nanocatalysts were evaluated in the cycloisomerization of alkynoic acids and demonstrated to produce the corresponding alkylidene lactones in good to excellent yields under mild conditions. In addition to their high activity, the catalysts exhibit low degree of metal leaching and straight-forward recycling, which highlight the practical utility of MSNs as supports for nanocatalysts. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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| 9. |
- Xia, Changjiu, et al.
(författare)
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Heterogeneous oxidation of cyclohexanone catalyzed by TS-1 : Combined experimental and DFT studies
- 2015
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Ingår i: Cuihuà xuébào. - 0253-9837 .- 1872-2067. ; 36:6, s. 845-854
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Tidskriftsartikel (refereegranskat)abstract
- The reaction mechanism of the oxidation of cyclohexanone catalyzed by titanium silicate zeolite Received 26 February 21515 TS-1 using aqueous H2O2 as the oxidant was investigated by combining density function theory (DFT) calculations with experimental studies. DFT calculations showed that H2O2 was adsorbed and activated at the tetrahedral Ti sites. By taking into account the adsorption energy, molecular size, steric hindrance and structural information, a reaction mechanism of Baeyer-Villiger oxidation catalyzed by TS-1 that involves the activation of H2O2 was proposed. Experimental studies showed that the major products of cyclohexanone oxidation by H2O2 catalyzed by a hollow TS-1 zeolite were epsilon-carprolactone, 6-hydroxyhexanoic acid, and adipic acid. These products were analyzed by GC-MS and were in good agreement with the proposed mechanism. Our studies showed that the reaction mechanism on TS-1 zeolite was different from that on Sn-beta zeolite.
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| 10. |
- Yu, Meijuan, et al.
(författare)
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3D local structure around Zn in Kti11p as a representative Zn-(Cys)4 motif as obtained by MXAN
- 2008
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - : Elsevier BV. - 0006-291X .- 1090-2104. ; 374:1, s. 28-32
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Tidskriftsartikel (refereegranskat)abstract
- Zinc is an important component of many proteins that play key roles in transcription, translation, and catalysis. Kti11p, DESR1, both belonging to a protein family characterized by a CSL zinc finger domain, and the co-catalytic zinc-protein PML containing a Zn2+ binding domain called RING or C3HC4 finger are all structurally determined by NMR although the zinc sites are silent to this spectroscopical method. The comparison of X-ray absorption near-edge spectroscopy (XANES) data for the three proteins demonstrates that fingerprints effect is a reliable method for a primary characterization of ligand species. Ab initio full MS Calculations performed by MAN are applied to obtain chemical and stereo structural information around the Zn ion in Kti11p. For the first time this high-spatial resolution technique confirms the formation of a stable Zn tetrahedral configuration with four sulfur ligands, and returns extremely accurate bond angle information between ligands.
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