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钨酸盐表面氢离子局部浓度对酸催化乙醇脱水的影响
作者:小柯机器人 发布时间:2021/11/26 13:56:54

扬州大学施慧团队报道了钨酸盐表面氢离子局部浓度对酸催化乙醇脱水的影响。相关研究成果于2021年11月23日发表于国际一流学术期刊《美国化学会杂志》。

以ZrO2、Al2O3、TiO2和活性炭为载体的钨酸盐结构域极大地影响了氢离子催化的醇水相脱水。对于所有催化剂而言,单钨酸盐的环己醇脱水速率均归一化为Brnsted酸中心浓度(周转频率,TOF)低于多钨酸盐和更大的WO3微晶。当达到或超过钨酸盐的单层覆盖率时,TOF是恒定的,与表面结构的特定性质无关,表面结构随表面W负载不断演变。然而,具有多钨酸盐和大WO3微晶的TOF强烈依赖于底层载体(例如,WOx/C催化剂的活性比WOx/Al2O3催化剂高10-50倍)。

负电荷WOx畴周围的双电层(EDL)包含水合离子,其局部浓度随载体的变化而变化。界面离子浓度的变化(“局部离子强度”)影响了反应醇的过量化学势,并导致TOF的显著差异。初级H/D动力学同位素效应(~3)以及实质上的正活化熵(111–195 J mol–1 K–1)表明,C–H(D)键断裂参与E1型机械序列的动力学相关步骤,而不考虑载体类型。该文中观察到的环烷醇水相脱水催化活性的显著载体依赖性,可能适用于对离子强度敏感的一系列氢离子催化的有机反应。

附:英文原文

Title: Impact of the Local Concentration of Hydronium Ions at Tungstate Surfaces for Acid-Catalyzed Alcohol Dehydration

Author: Niklas Pfriem, Yue Liu, Florian Zahn, Hui Shi, Gary L. Haller, Johannes A. Lercher

Issue&Volume: November 23, 2021

Abstract: Tungstate domains supported on ZrO2, Al2O3, TiO2, and activated carbon drastically influence the hydronium-ion-catalyzed aqueous-phase dehydration of alcohols. For all catalysts, the rate of cyclohexanol dehydration normalized to the concentration of Brnsted acid sites (turnover frequencies, TOFs) was lower for monotungstates than for polytungstates and larger crystallites of WO3. TOFs were constant when reaching or exceeding the monolayer coverage of tungstate, irrespective of the specific nature of surface structures that continuously evolve with the surface W loading. However, the TOFs with polytungstates and large WO3 crystallites depend strongly on the underlying support (e.g., WOx/C catalysts are 10–50-fold more active than WOx/Al2O3 catalysts). The electrical double layer (EDL) surrounding the negatively charged WOx domains contains hydrated hydronium ions, whose local concentrations change with the support. This varying concentration of interfacial hydronium ions (“local ionic strength”) impacts the excess chemical potential of the reacting alcohols and induces the marked differences in the TOFs. Primary H/D kinetic isotope effects (~3), together with the substantially positive entropy of activation (111–195 J mol–1 K–1), indicate that C–H(D) bond cleavage is involved in the kinetically relevant step of an E1-type mechanistic sequence, regardless of the support identity. The remarkable support dependence of the catalytic activity observed here for the aqueous-phase dehydration of cycloalkanols likely applies to a broad set of hydronium-ion-catalyzed organic reactions sensitive to ionic strength.

DOI: 10.1021/jacs.1c07203

Source: https://pubs.acs.org/doi/10.1021/jacs.1c07203

 

期刊信息

JACS:《美国化学会志》,创刊于1879年。隶属于美国化学会,最新IF:14.612
官方网址:https://pubs.acs.org/journal/jacsat
投稿链接:https://acsparagonplus.acs.org/psweb/loginForm?code=1000