A critical assessment of the roles of water molecules and solvated ions in acid-base-catalyzed reactions at solid-water interfaces  

固-水界面的酸碱催化反应中水分子和溶剂化离子的角色

作　　者：Xugang Yang Zonghui Liu Guoliang Wei Yu Gu Hui Shi 杨旭港;刘宗辉;魏国良;顾宇;施慧(扬州大学化学化工学院,江苏扬州225009;常州大学石油化工学院,江苏省绿色催化材料与技术重点实验室,江苏常州213164)

机构地区：[1]School of Chemistry and Chemical Engineering,Yangzhou University,Yangzhou 225009,Jiangsu,China [2]Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology,School of Petrochemical Engineering,Changzhou University,Changzhou 213164,Jiangsu,China

出　　处：《Chinese Journal of Catalysis》2022年第8期1964-1990,共27页催化学报（英文）

基　　金：国家自然科学基金(22072128).

摘　　要：Solid-aqueous interfaces and phenomena occurring at those interfaces are ubiquitously found in a plethora of chemical systems.When it comes to heterogeneous catalysis,however,our understanding of chemical transformations at solid-aqueous interfaces is relatively limited and primitive.This review phenomenologically describes a selection of water-engendered effects on the catalytic behavior for several prototypical acid-base-catalyzed reactions over solid catalysts,and critically assesses the general and special roles of water molecules,structural moieties derived from water,and ionic species that are dissolved in it,with an aim to extract novel concepts and principles that underpin heterogeneous acid-base catalysis in the aqueous phase.For alcohol dehydration catalyzed by solid Bronsted acids,rate inhibition by water is most typically related to the decrease in the acid strength and/or the preferential solvation of adsorbed species over the transition state as water molecules progressively solvate the acid site and form extended networks wherein protons are mobilized.Water also inhibits dehydration kinetics over most Lewis acid-base catalysts by competitive adsorption,but a few scattered reports reveal substantial rate enhancements due to the conversion of Lewis acid sites to Brønsted acid sites with higher catalytic activities upon the introduction of water.For aldol condensation on catalysts exposing Lewis acid-base pairs,the addition of water is generally observed to enhance the rate when C–C coupling is rate-limiting,but may result in rate inhibition by site-blocking when the initial unimolecular deprotonation is rate-limiting.Water can also promote aldol condensation on Brønsted acidic catalysts by facilitating inter-site communication between acid sites through hydrogen-bonding interactions.For metallozeolite-catalyzed sugar isomerization in aqueous media,the nucleation and networking of intrapore waters regulated by hydrophilic entities causes characteristic enthalpy-entropy tradeoffs as these water moi固体和水所形成的界面在各类化学和生物体系中非常常见,围绕相关物化现象的研究也一直是界面科学的前沿热点.然而,多相催化研究中对固-液界面发生的催化转化过程背后的微观机制的认识依旧十分有限,再加上水的诸多特殊理化性质,理解固-水界面的多相催化反应极具挑战性.本综述针对三类代表性的酸碱催化反应(醇类脱水、羟醛缩合和糖类异构),总结了一系列水(包括水分子本身、溶于其中的离子和由水衍生而来的其他物种)在这些体系中对表界面催化行为、反应机理和构效关系的常见影响方式,并批判性地归纳了业已提出的分子层面的观点和解释.当水的化学势较高(液态水或者水分压较大)时,其通常会抑制固体酸碱表面的催化反应,原因可以归结为:水分子在表面活性位上的竞争吸附、对活性位酸碱强度的削弱和对中间物种的溶剂化稳定作用(从而提高活化自由能能垒).水的存在也可造成活性位性质发生变化(例如活性较低的Lewis酸向活性更高的Brønsted酸转化),或直接/间接开辟新的反应路径,从而提高催化反应速率.此外,最新研究还揭示了活性位和表面反应物种(包括过渡态)溶剂化过程中许多重要的微观现象,包括:水在限域孔道内形成团簇结构和横跨活性位的溶剂链、表面酸性质子发生转移和迁移、高(水合氢)离子浓度的纳米级限域介电环境等.这些复杂的化学过程都会改变反应中关键中间体和过渡态的能量稳定性,从而显著影响催化剂的催化活性、选择性和稳定性.虽然从现有研究中已能挖掘出一些普适性的规律和原则,但有关固-水界面催化中不少现象和效应的解释仍局限于特定体系(水的物相、反应类型、条件和化学微环境等).在各种错综复杂的因素中,着重关注氢键相互作用和界面水合离子在水相和富水液相体系中的酸碱催化反应里的独特

关 键 词：Acid-base catalysis Solid-aqueous interfaces Water Aqueous-phase reaction Hydronium ion Hydrogen-bonding interaction Local ionic strength effect 

分 类 号：TQ203.2[化学工程—有机化工]