Trachta Michal, Bludský Ota, Vaculík Jan, Bulánek Roman, Rubeš Miroslav
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 162 10, Prague, Czech Republic.
Department of Physical Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, 532 10, Pardubice, Czech Republic.
Sci Rep. 2023 Jul 31;13(1):12380. doi: 10.1038/s41598-023-39667-5.
Understanding the adsorption behavior of base probes in aluminosilicates and its relationship to the intrinsic acidity of Brønsted acid sites (BAS) is essential for the catalytic applications of these materials. In this study, we investigated the adsorption properties of base probe molecules with varying proton affinities (acetonitrile, acetone, formamide, and ammonia) within six different aluminosilicate frameworks (FAU, CHA, IFR, MOR, FER, and TON). An important objective was to propose a robust criterion for evaluating the intrinsic BAS acidity (i.e., state of BAS deprotonation). Based on the bond order conservation principle, the changes in the covalent bond between the aluminum and oxygen carrying the proton provide a good description of the BAS deprotonation state. The ammonia and formamide adsorption cause BAS deprotonation and cannot be used to assess intrinsic BAS acidity. The transition from ion-pair formation, specifically conjugated acid/base interaction, in formamide to strong hydrogen bonding in acetone occurs within a narrow range of base proton affinities (812-822 kJ mol). The adsorption of acetonitrile results in the formation of hydrogen-bonded complexes, which exhibit a deprotonation state that follows a similar trend to the deprotonation induced by acetone. This allows for a semi-quantitative comparison of the acidity strengths of BAS within and between the different aluminosilicate frameworks.
了解碱探针在铝硅酸盐中的吸附行为及其与布朗斯特酸位点（BAS）固有酸度的关系对于这些材料的催化应用至关重要。在本研究中，我们研究了六种不同铝硅酸盐骨架（FAU、CHA、IFR、MOR、FER和TON）中具有不同质子亲和力的碱探针分子（乙腈、丙酮、甲酰胺和氨）的吸附特性。一个重要目标是提出一个可靠的标准来评估BAS的固有酸度（即BAS去质子化状态）。基于键序守恒原理，携带质子的铝和氧之间共价键的变化很好地描述了BAS去质子化状态。氨和甲酰胺的吸附会导致BAS去质子化，因此不能用于评估BAS的固有酸度。从甲酰胺中离子对形成，特别是共轭酸/碱相互作用，到丙酮中强氢键的转变发生在较窄的碱质子亲和力范围内（812 - 822 kJ/mol）。乙腈的吸附导致形成氢键络合物，其去质子化状态与丙酮诱导的去质子化呈现相似趋势。这使得可以对不同铝硅酸盐骨架内部和之间BAS的酸度强度进行半定量比较。
