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Determination of the Gas-phase Acidities of Oligopeptides
Published on: June 24, 2013
半孔性酸具有有序的六角结构,强酸性,在高温下具有非凡的热水稳定性
Journal of the American Chemical Society
|July 18, 2001
概括
高序列的中性酸 (MAS-5) 被合成,具有特殊的热稳定性. 这些先进材料表现出卓越的催化活性和对裂变和化反应的选择性.
科学领域:
- 材料科学 材料科学 材料科学
- 催化剂是一种催化剂.
- 纳米技术 纳米技术
背景情况:
- 半孔材料在催化应用中具有较大的表面积和可调节的孔径.
- 酸是广泛使用的催化剂,但往往遭受有限的热水稳定性.
- 开发稳定,高度活跃的半孔类酸盐对于先进的化学过程至关重要.
研究的目的:
- 合成具有高度排序的六角形半孔酸 (MAS-5) 具有均的孔径.
- 研究合成的MAS-5材料的结构,热和催化性能.
- 为了比较MAS-5的性能与现有的催化材料,如MCM-41和热石.
主要方法:
- 通过凝的热水处理合成酸前体.
- 使用 cetyltrimethylammonium bromide (CTAB) 表面活性剂组装中孔结构.
- 使用包括红外,紫外-拉曼和NMR光谱等技术进行表征.
- 在沸水和蒸汽中评估热稳定性.
- 在裂变和化反应中对催化活性和选择性的评估.
主要成果:
- 成功合成了高度排序的六角性中性酸盐 (MAS-5).
- 证明了特殊的热水稳定性,在沸水中持续超过300小时,在蒸汽中在800°C下持续2小时.
- 马斯-5的酸强度明显高于MCM-41,与贝塔热石相比.
- 与MCM-41和HZSM-5相比,在1,3,5-三烯裂解和异布坦化中具有更高的催化活性和选择性.
- 鉴定表明,MAS-5具有具有岩类结构单元的中孔和微孔.
结论:
- MAS-5代表了一种具有显著热稳定的新型中性酸盐类.
- 独特的孔隙结构和MAS-5的强酸性有助于其增强的催化性能.
- 这些发现为开发具有更高效率和耐久性的先进催化剂开辟了道路.
相关概念视频
Acid/Base Strengths and Dissociation Constants
The relative strength of an acid or base is the extent to which it ionizes when dissolved in water. If the ionization reaction is essentially complete, the acid or base is termed strong; if relatively little ionization occurs, the acid or base is weak. There are many more weak acids and bases than strong ones. The most common strong acids and bases are listed below:
Water: A Bronsted-Lowry Acid and Base
The reaction between a Brønsted-Lowry acid and water is called acid ionization. For example, when hydrogen fluoride dissolves in water and ionizes, protons are transferred from hydrogen fluoride molecules to water molecules, yielding hydronium ions and fluoride ions:
Acid Strength and Molecular Structure
Binary Acids and Bases
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
Acid and Bases: Ka, pKa, and Relative Strengths
This lesson delves into a critical aspect of the relative strengths of acids and bases. The strength of an acid is evaluated by the acid dissociation into its conjugate base and a hydronium ion in water. The complete dissociation of a strong acid is confirmed with a very high concentration of hydronium ions. As a result, an incomplete dissociation process affirms a weak acid. Therefore, the equilibrium is in the forward direction for strong acids and backward for weak acids in these reactions.
Molecular Structure and Acidity
An acid can be deprotonated to form a conjugate base or an anion. If the produced anion is more stable, then the acid is stronger. On the contrary, if the anion is unstable, then the acid is weaker. Hence, to determine the acidity of the compound, the stability of its conjugate base is studied using various factors.
The size effect explains the change in atomic size on acidity. When comparing the acids formed from elements that belong to the same column in the periodic table, their atomic sizes...
The size effect explains the change in atomic size on acidity. When comparing the acids formed from elements that belong to the same column in the periodic table, their atomic sizes...
Basicity of Aliphatic Amines
Amines can behave as Brønsted–Lowry bases by accepting a proton from the acid to form corresponding conjugate acids. Due to a lone pair of nonbonding electrons, aliphatic amines can also act as Lewis bases by forming a covalent bond with an electrophile.
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...

