A nuclear magnetic resonance probe for in situ studies of adsorbed species on catalysts

Solid acid catalysts have been widely used in petrochemical industry and their catalytic activities are normally dictated by their acidities. Unlike conventional acidity characterization techniques such as titration, infrared, or temperature-programmed desorption, detailed acid features of solid acids, such as type, distribution, concentration, and strength of acid sites may be attained by advanced methods involving pertinent probe molecules and state-of-the-art solid-state nuclear magnetic resonance (SSNMR) techniques, i.e. double resonance and two-dimensional correlation spectroscopies. In addition, in situ solid-state NMR method is capable of probing the guest/host properties of the reactant at the active centers of the catalysts as well as the intermediate species formed during conversion. It provides direct experimental evidence for exploring the mechanism of catalytic reaction. In this report, the fundamental theory and the recent developments in solid-state NMR are reviewed with specific focus on relevant applications in structure and acidity characterization of solid acid catalysts and catalytic mechanisms.固体酸催化剂广泛应用于现代石油与化学工业中, 其反应活性与其酸性密切相关. 与传统的酸性表征方法(红外光谱、程序升温脱附、滴定等)相比, 利用先进的探针分子技术、双共振和二维相关谱等核磁共振(NMR)技术可以获取固体催化剂酸种类、酸分布、酸浓度和酸强度等完整信息. 同时, 原位固体NMR实验可跟踪反应分子在催化剂活性中心吸附状态和转换的中间体物种, 为揭示反应机理提供了最直接的实验证据. 本文详细介绍了固体NMR的原理和一系列相关新技术, 着重综述了固体NMR技术在酸催化剂结构、活性中心特性以及催化反应机理方面的应用进展.