Department of Chemistry and Catalysis Research Center, Technical University of Munich, Lichtenbergstrasse 4, 85747, Garching, Germany.
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering, East China Normal University, 200062, Shanghai, P. R. China.
Angew Chem Int Ed Engl. 2023 Jan 16;62(3):e202208693. doi: 10.1002/anie.202208693. Epub 2022 Dec 8.
The intracrystalline ionic environment in microporous zeolite can remarkably modify the excess chemical potential of adsorbed reactants and transition states, thereby influencing the catalytic turnover rates. However, a limit of the rate enhancement for aqueous-phase dehydration of alcohols appears to exist for zeolites with high ionic strength. The origin of such limitation has been hypothesized to be caused by the spatial constraints in the pores via, e.g., size exclusion effects. It is demonstrated here that the increase in turnover rate as well as the formation of a maximum and the rate drop are intrinsic consequences of the increasingly dense ionic environment in zeolite. The molecularly sized confines of zeolite create a unique ionic environment that monotonically favors the formation of alcohol-hydronium ion complexes in the micropores. The zeolite microporous environment determines the kinetics of catalytic steps and tailors the impact of ionic strength on catalytic rates.
微孔沸石中晶内离子环境可显著改变吸附反应物和过渡态的过剩化学势，从而影响催化转化速率。然而，对于离子强度较高的沸石，水相醇脱水的速率增强似乎存在一个极限。这种限制的原因被假设为是由于孔内的空间限制，例如，尺寸排除效应。本文证明，转化率的增加以及最大值的形成和速率下降都是沸石中离子环境越来越密集的内在结果。沸石的分子尺寸限制创造了一种独特的离子环境，在微孔中有利于醇-质子离子配合物的形成。沸石的微孔环境决定了催化步骤的动力学，并调整了离子强度对催化速率的影响。
