This review provides a comprehensive elucidation of the fundamental mechanisms and key interactions governing molecular diffusion under nanoconfinement in zeolites.

Zeolites are indispensable catalysts in a wide range of industrial applications due to their well-defined microporous structures and exceptional shape-selective properties. However, their practical use is often constrained by diffusion limitations, which can hinder reactant accessibility, influence product selectivity, and accelerate catalyst deactivation. This review critically examines strategies to alleviate these diffusion constraints, focusing on hierarchical structuring, nanozeolite synthesis, and advanced shaping techniques. We discuss fundamental diffusion theories, experimental characterization methods, and emerging methodologies that enhance mass transport in zeolites. By bridging fundamental principles with industrial applications, this review provides a comprehensive overview of how tailored zeolite architectures can optimize catalytic performance, paving the way for more efficient and sustainable processes.

Hierarchical Al-rich MOR zeolites with an intracrystalline mesopore centered at 10–20 nm were synthesized by a tandem fluorination-acid leaching-alkaline treatment protocol.

Metal hydrides (M-H) on solid surfaces, i.e., surface M-H, are ubiquitous but critical species in heterogeneous catalysis, and their intermediate roles have been proposed in numerous reactions such as (de)hydrogenation and alkanes activation, etc., however, the detailed spectroscopic characterizations remain challenging. Solid-state nuclear magnetic resonance (ssNMR) spectroscopy has become a powerful tool in surface studies, as it provides access to local structural characterizations at atomic level from multiple views, with comprehensive information on chemical bonding and spatial structures. In this review, we summarized and discussed the latest research developments on the successful application of ssNMR to characterize surface M-H species on solid catalysts including supported single-site heterogeneous catalysts, bulk metal oxides and metal-modified zeolites. We also discussed the opportunities and challenges in this field, as well as the potential application/development of state-of-the-art ssNMR technologies to enable further exploration of metal hydrides in heterogeneous catalysis.© 2022 The Authors.

固体核磁共振（NMR）因对结构和化学环境敏感，已广泛应用于研究金属有机框架材料（MOFs）在吸附分离应用上的主客体相互作用机制．多核、多维、变温固体NMR实验可以用来研究低碳碳氢化合物、CO₂在MOFs孔道内的吸附行为（包括优先吸附位点、动力学性质、扩散快慢等）．固体NMR也可用来直接测定低碳烷烃/烯烃在MOFs中的分离选择性，并观测低碳烷烃/烯烃在MOFs孔道内的竞争优先吸附．此外，固体NMR还可用来揭示常见化学品与MOFs的主客体相互作用模式．这些研究的开展将有助于人们理解MOFs在吸附和分离过程中存在的内在构效关系．

Acid-base catalytic reaction, either in heterogeneous or homogeneous systems, is one of the most important chemical reactions that has provoked a wide variety of industrial catalytic processes for production of chemicals and petrochemicals over the past few decades. In view of the fact that the catalytic performances (e.g., activity, selectivity, and reaction mechanism) of acid-catalyzed reactions over acidic catalysts are mostly dictated by detailed acidic features, viz. type (Brønsted vs Lewis acidity), amount (concentration), strength, and local environments (location) of acid sites, information on and manipulation of their structure-activity correlation are crucial for optimization of catalytic performances as well as innovative design of novel effective catalysts. This review aims to summarize recent developments on acidity characterization of solid and liquid catalysts by means of experimental P nuclear magnetic resonance (NMR) spectroscopy using phosphorus probe molecules such as trialkylphosphine (TMP) and trialkylphosphine oxides (RPO). In particular, correlations between the observed P chemical shifts (δP) of phosphorus (P)-containing probes and acidic strengths have been established in conjuction with density functional theory (DFT) calculations, rendering practical and reliable acidity scales for Brønsted and Lewis acidities at the atomic level. As illustrated for a variety of different solid and liquid acid systems, such as microporous zeolites, mesoporous molecular sieves, and metal oxides, the P NMR probe approaches were shown to provide important acid features of various catalysts, surpassing most conventional methods such as titration, pH measurement, Hammett acidity function, and some other commonly used physicochemical techniques, such as calorimetry, temperature-programmed desorption of ammonia (NH-TPD), Fourier transformed infrared (FT-IR), and H NMR spectroscopies.

Zeolite-catalyzed methanol-to-olefin (MTO) and methanol-to-ethanol (MTE) reactions have achieved significant breakthroughs in both industry and academia, proving to be mature alternative pathways for producing basic chemicals from non-oil resources. The successful transition of these catalytic processes from laboratory to industrial implementation has been propelled by fundamental breakthroughs in the comprehensive understanding of reaction mechanisms. In this context, solid-state nuclear magnetic resonance (ssNMR) spectroscopy has emerged as an indispensable tool for elucidating catalyst structures, catalytic reaction mechanisms, and the interactions and dynamics of reactant molecules in these industrially important processes. This review specifically focuses on the application of ssNMR spectroscopy in industrially mature MTO and dimethyl ether (DME) carbonylation processes, which serve as representative examples of zeolite-catalyzed industrial processes. Based on this molecular-level information from spectroscopic observations combined with theoretical methods, this review aims to bridge the fundamental understandings of reaction mechanisms with practical applications, including the rationalization of catalysts, the optimization of catalytic performance, and the improvement of industrial processes.

Zeolites are widely used in many commercial processes, mostly as catalysts or adsorbents. Understanding their intimate structure at the nanoscale is the key to control their properties and design the best materials for their ever increasing uses. Herein, we report a new and controllable fluoride treatment for the non-discriminate extraction of zeolite framework cations. This sheds new light on the sub-structure of commercially relevant zeolite crystals: they are segmented along defect zones exposing numerous nanometer-sized crystalline domains, separated by low-angle boundaries, in what were apparent single-crystals. The concentration, morphology, and distribution of such domains analyzed by electron tomography indicate that this is a common phenomenon in zeolites, independent of their structure and chemical composition. This is a milestone to better understand their growth mechanism and rationally design superior catalysts and adsorbents.© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zeolites have exceptional catalytic performance in oil refining and chemical synthesis that can be attributed to their well-defined porous structures that host active sites. This study pinpoints the exact locations of aluminum atoms in ZSM-5 structures-a key zeolite catalyst. Aluminum siting governs catalytic efficiency in acid and redox processes. Anomalous x-ray powder diffraction (AXRPD) at the aluminum K-edge probes the long-range order of aluminum atoms within the ZSM-5 frameworks, precisely quantifying both isolated aluminum atoms and Al(-O-Si-O-)Al sequences (aluminum pairs). Supported by nuclear magnetic resonance studies, AXRPD unambiguously determines the crystallographic organization of aluminum pairs, recognized spectroscopically as α, β, and γ sites, linking their distribution to superior catalytic activity in propene oligomerization. This combined approach provides essential insights for optimizing zeolite catalysts and enhancing their performance.

Further progress in the field of heterogeneous catalysis depends on our knowledge of the nature and behavior of surface sites on solid catalysts and of the mechanisms of chemical reactions catalyzed by these materials. In the past decades, solid-state NMR spectroscopy has been developed to an important tool for routine characterization of solid catalysts. The present work gives a review on experimental approaches and applications of solid-state NMR spectroscopy for investigating Brønsted and Lewis sites on solid acids. Studies focusing on the generation of surface sites via post-synthesis modification routes of microporous and mesoporous materials support the development of new and the improvement of existing catalyst systems. High-temperature and flow techniques of in situ solid-state NMR spectroscopy allow a deeper insight into the mechanisms of heterogeneously catalyzed reactions and open the way for studying the activity of acidic surface sites. They help to clarify the activation of reactants on Brønsted and Lewis acid sites and improve our understanding of mechanisms affecting the selectivity of acid-catalyzed reactions.Copyright © 2011 Elsevier Inc. All rights reserved.

Elucidating the nature, strength, and siting of acid sites in zeolites is fundamental to fathom their reactivity and catalytic behavior. Despite decades of research, this endeavor remains a major challenge. Trimethylphosphine oxide (TMPO) has been proposed as a reliable probe molecule to study the acid properties of solid acid catalysts, allowing the identification of distinct Brønsted and Lewis acid sites and the assessment of Brønsted acid strengths. Recently, doubts have been raised regarding the assignment of the P NMR resonances of TMPO-loaded zeolites. Here, it is shown that a judicious control of TMPO loading combined with two-dimensional H-P HETCOR solid-state NMR, DFT, and ab initio molecular dynamics (AIMD)-based computational modeling provides an unprecedented atomistic description of the host-guest and guest-guest interactions of TMPO molecules confined within HZSM-5 molecular-sized voids. P NMR resonances usually assigned to TMPO molecules interacting with Brønsted sites of different acid strength arise instead from both changes in the probe molecule confinement effects at ZSM-5 channel system and the formation of protonated TMPO dimers. Moreover, DFT/AIMD shows that the H and P NMR chemical shifts strongly depend on the siting of the framework aluminum atoms. This work overhauls the current interpretation of NMR spectra, raising important concerns about the widely accepted use of probe molecules for studying acid sites in zeolites.