Department of Chemistry and Catalysis Research Institute, Technische Universität München , Lichtenbergstrasse 4, 85748 Garching, Germany.
Institute for Integrated Catalysis, Pacific Northwest National Laboratory , P.O. Box 999, Richland, Washington 99352, United States.
J Am Chem Soc. 2015 Dec 23;137(50):15781-94. doi: 10.1021/jacs.5b09107. Epub 2015 Dec 10.
The Brønsted acid-catalyzed gas-phase dehydration of 1-propanol (0.075-4 kPa) was studied on zeolite H-MFI (Si/Al = 26, containing minimal amounts of extra framework Al moieties) in the absence and presence of co-fed water (0-2.5 kPa) at 413-443 K. It is shown that propene can be formed from monomeric and dimeric adsorbed 1-propanol. The stronger adsorption of 1-propanol relative to water indicates that the reduced dehydration rates in the presence of water are not a consequence of the competitive adsorption between 1-propanol and water. Instead, the deleterious effect is related to the different extents of stabilization of adsorbed intermediates and the relevant elimination/substitution transition states by water. Water stabilizes the adsorbed 1-propanol monomer significantly more than the elimination transition state, leading to a higher activation barrier and a greater entropy gain for the rate-limiting step, which eventually leads to propene. In a similar manner, an excess of 1-propanol stabilizes the adsorbed state of 1-propanol more than the elimination transition state. In comparison with the monomer-mediated pathway, adsorbed dimer and the relevant transition states for propene and ether formation are similarly, while less effectively, stabilized by intrazeolite water molecules.
在不存在和存在共进料水（0-2.5 kPa）的情况下，在 413-443 K 下，研究了 Brønsted 酸催化的气相 1-丙醇（0.075-4 kPa）脱水在 H-MFI 沸石（Si/Al = 26，含有最少的骨架外 Al 部分）上的反应。结果表明，丙烯可以从单体和二聚体吸附的 1-丙醇形成。与水相比，1-丙醇的吸附较强，表明在存在水的情况下，脱水速率降低不是 1-丙醇和水之间竞争吸附的结果。相反，有害影响与水对吸附中间体和相关消除/取代过渡态的稳定程度不同有关。水显著稳定吸附的 1-丙醇单体，比稳定消除过渡态的能力要强，这导致限速步骤的活化能增加，熵增加，最终生成丙烯。以类似的方式，过量的 1-丙醇稳定吸附的 1-丙醇状态比稳定消除过渡态要强。与单体介导的途径相比，吸附的二聚体和形成丙烯和醚的相关过渡态，虽然效果较差，但同样被分子筛内的水分子稳定。
