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制备条件对SAPO—34分子筛结构及MTO活性的影响 总被引:5,自引:0,他引:5
用水热法合成SAPO-34分子筛,XRD分析和微反评价表明,改变物料配比可能形成纯净的SAPO-5分子筛、SAPO-34分子筛、SAPO-5和SAPO-34混晶或无定形物质,不同产品的MTO催化性能也不相同;不同的模板剂虽然能够诱发SAPO-34晶核的产生,合成纯的SAPO-34晶体,但用不同模板剂合成的分子筛在晶体结构及催化活性方面存在明显的差别,以三乙胺(Et3N)为模板剂合成的SAPO-34催化性能及晶体稳定性优于以二乙胺(DRA)为模板剂合成的SAPO-34;焙烧过程对晶体完美程度有很明显的影响,而且也可能改变晶胞尺寸,使晶体XRD衍射峰位发生移动 相似文献
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CoAPSO-34分子筛的合成与性能 总被引:3,自引:0,他引:3
以三乙胺为模板剂,在碱性条件下用水热晶化法将钴元素引入了硅磷铝分子筛骨架,合成出CoAPSO-34分子筛.实验表明,在碱性介质中以低价态引入的钴元素首先转化为高价态Co(Ⅲ),然后才进入分子筛骨架。利用X射线粉末衍射和红外光谱对其进行了结构分析,确认钴元素进入了分子筛骨架.利用程序升温氨脱附和氨法红外光谱考察了CoAPSO-34的表面酸性.将CoAPSO-34用作甲醇转化的催化剂时,随钴含量增高,催化剂稳定性下降,反应产物中C=2~C=4烯烃的选择性升高 相似文献
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对合成的SAPO-5分子筛进行了高温和水热处理,并用IR,XRD和MAS NMR对处理过的分子筛进行了表征。结果表明,短时间的高温焙烧并不破坏分子筛的结构,而使分子筛中的骨架元素P,Al和Si发生重构;长时间的高温焙烧使分子筛的结晶度降低,主要是由于P和Al游离出分子筛的骨架而形成磷酸铝盐。水热处理使分筛的Si经历一个转晶和重构过程,在使SAPO-5分子筛结构更加完整的同时,未完全结晶的杂质形成了 相似文献
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分别以三乙胺、四乙基氢氧化铵以及二者的混合物为模板剂,采用水热法合成了三种SAPO-34分子筛样品。用化学分析、XRD、TPD和IR方法研究了不同模板剂对SAPO-34分子筛性能的影响。实验结果表明,四乙基氢氧化铵有利于硅进入分子筛骨架;三乙胺有利于生成较多的强酸中心;将三乙胺与四乙基氢氧化铵联用,能有效地调变所合成的SAPO-34的酸中心分布,使其对甲醇转化制低碳烯烃具有较高的选择性。 相似文献
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Concetta Giancola 《Journal of Thermal Analysis and Calorimetry》2008,91(1):79-85
The aim of this work is to discuss the thermodynamic properties, obtained by differential scanning calorimetry (DSC), of the
thermal transition of proteins and nucleic acids and to analyze these data using statistical thermodynamic relations. The
denaturation of the ordered, specific structures of biological macromolecules is a cooperative process and in many cases the
macromolecules undergo a two-state transition. Differential scanning calorimetry, giving direct thermodynamic information,
has proved to be very useful in clarifying the energetics of macromolecule transitions and in characterizing their thermal
stability. Here, various examples are discussed: i) the equilibrium thermal denaturation of ribonuclease A, a model for the use of DSC by following the temperature-unfolding
of the proteins, a monomolecular transition; ii) the equilibrium thermal dissociation of a DNA double helix in two strands, an example of how DSC is used to follow a bimolecular
process; iii) an example of the use of DSC for studying the melting of unimolecular and tetramolecular DNA quadruple-helices. 相似文献
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Budrugeac P. Trandafir Viorica Albu Madalina Georgiana 《Journal of Thermal Analysis and Calorimetry》2003,72(2):581-585
The methods of the thermal analysis (TG, DTG and DTA) were used in order to investigate the effect of the hydration degree
on the thermal behaviour of some collageneous matrices. It was pointed out that the degradation of hydrated collagen in the
temperature range 20-400°C occurs through two successive processes accompanied by mass losses. The first process, consisting
in the collagen dehydration, is endothermic and takes place in the temperature range ≈25 - ≈125°C. The second process is exothermic
and consists in the decomposition and/or thermo-oxidation of dry collagen. The thermal parameters of both processes depend
on the hydration degree of collagen. The observed dependencies show that the hydrothermal and thermo-oxidative stability of
collagen are strongly correlated with its water content.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Anirban Dutta Sumit K. Dutta Samrat Das Adhikari Dr. Narayan Pradhan 《Angewandte Chemie (International ed. in English)》2018,57(29):9083-9087
High temperature colloidal synthesis for obtaining thermal, colloidal and phase‐stable CsPbI3 nanocrystals with near‐unity quantum yield is reported. While standard perovskite synthesis reactions were carried out at 160 °C (below 200 °C), increase of another ≈100 °C enabled the alkylammonium ions to passivate the surface firmly and prevented the nanocrystals from phase transformation. This did not require any inert atmosphere storage, use of heteroatoms, specially designed ligands, or the ice cooling protocol. Either at high temperature in reaction flask or in the crude mixture or purified dispersed solution; these nanocrystals were observed stable and retained the original emission. Different spectroscopic analyses were carried out and details of the surface binding of alkyl ammonium ligands in place of surface Cs in the crystal lattice were investigated. As CsPbI3 is one of the most demanding optical materials, bringing stability by proper surface functionalization without use of secondary additives would indeed help in wide spreading of their applications. 相似文献
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Tetraiodotrispirobifluorene (1) was synthesized through cyclization of 2,7-diiodofluorene with pentaerythrityl tetrabromide under base condition. Subsequent treatment of 1 with arylboronic acid or arylacetylene under Pd-catalyzed coupling condition led to corresponding tetraaryl trispirobifluorenes (3–8). These trispirobifluorene derivatives exhibited bright-violet to blue photoluminescence (PL) with excellent quantum efficiencies and showed high thermal stabilities. ‘Green-emission tail’ could not be detected for those tetraaryl substituted trispirobifluorenes (3–8) annealed both in N2 and in air. 相似文献
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John D. Sherwood 《Electrophoresis》2022,43(21-22):2104-2111
The electrophoretic velocity of a sphere within a liquid-filled circular cylinder in a direction parallel to the cylinder axis has been studied by Yariv and Brenner (Phys. Fluids 2002, 14, 3354–3357; SIAM J. Appl. Math. 2003, 64, 423–441). We use their analyses of the electric field in order to determine the electrical force on the sphere along the cylinder radius (i.e., perpendicular to its axis) when either the radius of the sphere is small compared to that of the cylinder, or when the radius of the sphere is only slightly smaller than that of the cylinder. In both cases the force acts towards the centreline of the cylinder, and hence this force tends to stabilize electrophoresis of the sphere along the cylinder axis. 相似文献
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<正>A novel fluorene-bridged tetraketone monomer,9,9-bis[(4-benzilyloxy)phenyl]fluorene(FLTK) was synthesized and characterized.The tetraketone was polymerized with various aromatic tetraamines to afford a series of polyphenylquinoxalines(PPQs).The obtained polymers were found to be soluble in common organic solvents such as N-methyl-2-pyrrolidone(NMP),chloroform and m-cresol.Flexible and tough PPQ films obtained by spin-casting their NMP solutions exhibited tensile strengths higher than 60 MPa.The films also demonstrated good thermal stability up to 500℃in nitrogen and glass transition temperatures higher than 280℃.In addition,the PPQ films exhibited good hydrolytic stability. High surface and volume resistivity retentions were achieved for the films after immersion or boiling in water for 24 h. 相似文献
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Thermal and hydrothermal stabilities of the alkali-treated HZSM-5 zeolites 总被引:1,自引:0,他引:1 下载免费PDF全文
Yuning Li Dong Liu Shenglin Liu Wei Wang Sujuan Xie Xiangxue Zhu Longya Xu 《天然气化学杂志》2008,17(1):69-74
HZSM-5 zeolites with the micro-mesopore hierarchical porosity have been prepared by the post-synthesis of alkali-treatment, and their thermal and hydrothermal stabilities were studied using DTA, XRD, and NH3-TPD characterization techniques. Compared to the unmodified zeolite, the thermal and hydrothermal stabilities of the alkali-treated ZSM-5 zeolites were slightly deteriorated because of the introduction of mesopores caused by the desilication. Nevertheless, the alkali-treated zeolite framework could be maintained until the temperature increased to 1175 ℃. 相似文献
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Kristina Westerlund Anders Myrhammar Hanna Tano Maxime Gestin Amelie Eriksson Karlstrm 《Molecules (Basel, Switzerland)》2021,26(10)
Natural backbone-cyclized proteins have an increased thermostability and resistance towards proteases, characteristics that have sparked interest in head-to-tail cyclization as a method to stability-enhance proteins used in diagnostics and therapeutic applications, for example. In this proof-of principle study, we have produced and investigated a head-to-tail cyclized and HER2-specific ZHER2:342 Affibody dimer. The sortase A-mediated cyclization reaction is highly efficient (>95%) under optimized conditions, and renders a cyclic ZHER3:342-dimer with an apparent melting temperature, Tm, of 68 °C, which is 3 °C higher than that of its linear counterpart. Circular dichroism spectra of the linear and cyclic dimers looked very similar in the far-UV range, both before and after thermal unfolding to 90 °C, which suggests that cyclization does not negatively impact the helicity or folding of the cyclic protein. The cyclic dimer had an apparent sub-nanomolar affinity (Kd ~750 pM) to the HER2-receptor, which is a ~150-fold reduction in affinity relative to the linear dimer (Kd ~5 pM), but the anti-HER2 Affibody dimer remained a high-affinity binder even after cyclization. No apparent difference in proteolytic stability was detected in an endopeptidase degradation assay for the cyclic and linear dimers. In contrast, in an exopeptidase degradation assay, the linear dimer was shown to be completely degraded after 5 min, while the cyclic dimer showed no detectable degradation even after 60 min. We further demonstrate that a site-specifically DyLight 594-labeled cyclic dimer shows specific binding to HER2-overexpressing cells. Taken together, the results presented here demonstrate that head-to-tail cyclization can be an effective strategy to increase the stability of an Affibody dimer. 相似文献