Shetty Manish, Wang Huamin, Chen Feng, Jaegers Nicholas, Liu Yue, Camaioni Donald M, Gutiérrez Oliver Y, Lercher Johannes A
Institute of Integrated Catalysis, Pacific Northwest National Laboratory (PNNL), P.O. Box 999, Richland, WA, 99352, USA.
Department of Chemistry and Catalysis Research Center, Technical University München, Lichtenbergstrasse 4, 85747, München, Germany.
Angew Chem Int Ed Engl. 2021 Feb 1;60(5):2304-2311. doi: 10.1002/anie.202009835. Epub 2020 Nov 27.
Alkanol dehydration rates catalyzed by hydronium ions are enhanced by the dimensions of steric confinements of zeolite pores as well as by intraporous intermolecular interactions with other alkanols. The higher rates with zeolite MFI having pores smaller than those of zeolite BEA for dehydration of secondary alkanols, 3-heptanol and 2-methyl-3-hexanol, is caused by the lower activation enthalpy in the tighter confinements of MFI that offsets a less positive activation entropy. The higher activity in BEA than in MFI for dehydration of a tertiary alkanol, 2-methyl-2-hexanol, is primarily attributed to the reduction of the activation enthalpy by stabilizing intraporous interactions of the C -H transition state with surrounding alcohol molecules. Overall, we show that the positive impact of zeolite confinements results from the stabilization of transition state provided by the confinement and intermolecular interaction of alkanols with the transition state, which is impacted by both the size of confinements and the structure of alkanols in the E1 pathway of dehydration.
由水合氢离子催化的链烷醇脱水速率，会因沸石孔道的空间限制尺寸以及与其他链烷醇的孔内分子间相互作用而提高。对于仲链烷醇3-庚醇和2-甲基-3-己醇的脱水反应，具有比BEA沸石更小孔道的MFI沸石表现出更高的速率，这是由于MFI更紧密限制环境中的活化焓较低，抵消了不太正的活化熵。对于叔链烷醇2-甲基-2-己醇的脱水反应，BEA沸石比MFI沸石具有更高的活性，这主要归因于通过稳定C-H过渡态与周围醇分子的孔内相互作用而降低了活化焓。总体而言，我们表明沸石限制的积极影响源于限制作用提供的过渡态稳定以及链烷醇与过渡态的分子间相互作用，这在脱水的E1途径中受到限制尺寸和链烷醇结构的影响。
