中国科学院大连化学物理研究所陈魁智课题组报道了铝对的鉴定和定量及其对沸石脱铝的影响。相关论文发表在2025年2月25日出版的《美国化学会杂志》上。

为了解决这个问题，课题组提出了一个“双Al”和“单Al”水解模型，为Al对在沸石稳定性中的关键作用提供了新的见解。这项工作为优化沸石基催化剂的性能和寿命开辟了新的途径。

据介绍，了解沸石催化剂中成对铝（Al）位点的精确数量和空间分布是至关重要的，因为它们通过协同效应和长期稳定性显著影响催化性能。在这项研究中，采用不同阳离子大小的二价阳离子滴定，结合先进的定量1H NMR和1H - 1H同核相关技术，开发了一种新的策略，以准确识别和分类三种不同类型的Al对。这包括沿六元环（6-MRs）和十元环（10-MRs）排列的两种类型的Al对，后者基本上由位于不同6-MR或5-MR的Al原子组成。第三种类型由两个位于不同通道的Al原子组成。第二种和第三种类型在过去一直难以探测，但它们可能对催化作用至关重要，特别是第二种类型显示出足够接近Ba²⁺（半径为1.49 ）。他们量化每种Al对的策略标志着对沸石框架的理解取得了重大进展。

此外，以逐步蒸煮为主导的控制水热处理表明，较高浓度的Al对加速脱铝，主要是由于水分子的动力学原因，而不是由于Al对引起的固有结构不稳定性。

附：英文原文

Title: Identification and Quantification of Al Pairs and Their Impact on Dealumination in Zeolites

Author: Yuting Sun, Lixin Liang, Min Yang, Yi Ji, Guangjin Hou, Kuizhi Chen

Issue&Volume: February 25, 2025

Abstract: Understanding the precise quantity and spatial distribution of paired aluminum (Al) sites in zeolite catalysts is crucial, as they significantly impact the catalytic performance via synergistic effects and long-term stability. In this study, a novel strategy by employing divalent cation titration with varying cation sizes, in combination with advanced quantitative 1H NMR and 1H–1H homonuclear correlation techniques, has been developed to accurately identify and classify three distinct types of Al pairs. These include two types of Al pairs aligned along six-membered rings (6-MRs) and 10-membered rings (10-MRs), the latter of which are essentially composed of Al atoms located in different 6-MR or 5-MR. The third type comprises two Al atoms located in different channels. The second and third types had been challenging to probe in the past, yet they may be critical for catalysis, particularly the second type demonstrating proximity close enough to accommodate Ba2+ (with a radius of 1.49 ). Our strategy for quantifying each type of Al pair marks a significant advancement in the understanding of the zeolite framework. Furthermore, controlled hydrothermal treatments using stepwise steaming reveal that a higher concentration of Al pairs accelerates dealumination, primarily for dynamic reasons of water molecules but not intrinsic structural instability induced by Al pairs. To address this, we propose a “bi-Al” vs “mono-Al” hydrolysis model, offering fresh insights into the pivotal role of Al pairs on zeolite stability. This work opens new avenues for optimizing zeolite-based catalysts for enhanced performance and longevity.

DOI: 10.1021/jacs.4c14741

Source: https://pubs.acs.org/doi/abs/10.1021/jacs.4c14741