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The utilization of methane for chemical production, often considered as the future of petrochemistry, historically could not compete economically with conventional processes due to higher investment costs. Achieving sustainability and decarbonization of the downstream industry by integration with a methane-to-chemicals process may provide an opportunity to unlock the future for these technologies. Gas-to-chemicals is an efficient tool to boost the decarbonization potential of renewable energy. While the current implementation of carbon capture utilization and storage (CCUS) technologies is of great importance for industrial decarbonization, a shift to greener CO2-free processes and CO2 utilization from external sources for manufacturing valuable goods is highly preferred. This review outlines potential options for how a methane-to-chemicals process could support decarbonization of the downstream industry. [ABSTRACT FROM AUTHOR]

The mesopores formation in zeolite crystals has long been considered to occur through the stochastic hydrolysis and removal of framework atoms. Here, we investigate the NH4F etching of representative small, medium, and large pore zeolites and show that the zeolite dissolution behavior, therefore the mesopore formation probability, is dominated by zeolite architecture at both nano‐ and sub‐nano scales. At the nano‐scale, the hidden mosaics of zeolite structure predetermine the spatio‐temporal dissolution of the framework, hence the size, shape, location, and orientation of the mesopores. At the sub‐nano scale, the intrinsic micropore size and connectivity jointly determine the diffusivity of reactant and dissolved products. As a result, the dissolution propensity varies from removing small framework fragments to consuming nanodomains and up to full digestion of the outmost part of zeolite crystals. The new knowledge will lead to new understanding of zeolite dissolution behavior and new adapted strategies for tailoring hierarchical zeolites. [ABSTRACT FROM AUTHOR]

Zeolite Y and its ultra‐stabilized hierarchical derivative (USY) are the most widely used zeolite‐based heterogeneous catalysts in oil refining, petrochemisty, and other chemicals manufacturing. After almost 60 years of academic and industrial research, their resilience is unique as no other catalyst displaced them from key processes such as FCC and hydrocracking. The present study highlights the key difference leading to the exceptional catalytic performance of USY versus the parent zeolite Y in a multi‐technique study combining advanced spectroscopies (IR and solid‐state NMR) and molecular modeling. The results highlight a hitherto unreported proton transfer involving inaccessible active sites in sodalite cages that contributes to the exceptional catalytic performance of USY. [ABSTRACT FROM AUTHOR]

Zeolites have been game-changing materials in oil refining and petrochemistry over the last 60 years and have the potential to play the same role in the emerging processes of the energy and environmental transition. Although zeolites are crystalline inorganic solids, their structures are not perfect and the presence of defect sites – mainly Brønsted acid sites and silanols – influences their thermal and chemical resistance as well as their performances in key areas such as catalysis, gas and liquid separations and ion-exchange. In this paper, we review the type of defects in zeolites and the characterization techniques used for their identification and quantification with the focus on diffraction, spectroscopic and modeling approaches. More specifically, throughout the review, we will focus on silanol (Si–OH) defects located within the micropore structure and/or on the external surface of zeolites. The main approaches applied to engineer and heal defects and their consequences on the properties and applications of zeolites in catalysis and separation processes are highlighted. Finally, the challenges and opportunities of silanol defect engineering in tuning the properties of zeolites to meet the requirements for specific applications are presented. [ABSTRACT FROM AUTHOR]

Hierarchical zeolites are regarded as promising catalysts due to their well‐developed porosity, increased accessible surface area, and minimal diffusion constraints. Thus far, the focus has been on the creation of mesopores in zeolites, however, little is known about a microporosity upgrading and its effect on the diffusion and catalytic performance. Here the authors show that the "birth" of mesopore formation in faujasite (FAU) type zeolite starts by removing framework T atoms from the sodalite (SOD) cages followed by propagation throughout the crystals. This is evidenced by following the diffusion of xenon (Xe) in the mesoporous FAU zeolite prepared by unbiased leaching with NH4F in comparison to the pristine FAU zeolite. A new diffusion pathway for the Xe in the mesoporous zeolite is proposed. Xenon first penetrates through the opened SOD cages and then diffuses to supercages of the mesoporous zeolite. Density functional theory (DFT) calculations indicate that Xe diffusion between SOD cage and supercage occurs only in hierarchical FAU structure with defect‐contained six‐member‐ring separating these two types of cages. The catalytic performance of the mesoporous FAU zeolite further indicates that the upgraded microporosity facilitates the intracrystalline molecular traffic and increases the catalytic performance. [ABSTRACT FROM AUTHOR]

The crystallization kinetics of template free ultra-small FAU-type zeolite (X) in highly alkaline viscous precursor suspensions is investigated. We focus on understanding the crystallization pathway from a viscous amorphous precursor suspension to nanosized FAU crystals with high phase purity and yield. The crystallization develops in a four-step process: (1) preparation of a clear and stable precursor suspension by a controlled mixing of silica and alumina colloidal suspensions at low temperature (4 °C), (2) aging the colloidal suspension at room temperature, (3) partial evaporation of the water of the colloidal suspension to produce a highly viscous suspension with amorphous nanoparticles with a monomodal particle size distribution, (4) hydrothermal treatment at low temperature (50 °C) to transform the amorphous nanoparticles into FAU type nanocrystals with the same particle size while preventing agglomeration and sedimentation. The properties (size and morphology) of the amorphous particles depend on the mixing procedure (temperature and speed of mixing) and alkalinity of the colloidal suspension. High alkalinity of the suspension leads to the formation of ultra-small discrete nanoparticles with a monomodal particle size distribution. During the aging step (2), secondary building units characteristic of the FAU framework structure are detected (Raman and IR spectroscopies) in the amorphous aluminosilicate particles. During the evaporation of the water of the colloidal suspension (3), prior to hydrothermal synthesis, double-six membered rings (D6R), the secondary building units of the FAU structure, were detected by in situ29Si NMR spectroscopy. Formation of the very first micropores in the nanosized particles was further confirmed by HP 129Xe NMR spectroscopic measurements. [ABSTRACT FROM AUTHOR]

A commercial zeolite L is subjected to chemical etching with aqueous solutions of NH4F and NH4HF2 to generate secondary porosity. The derived samples are characterized by X‐ray diffraction, N2 adsorption, scanning, and transmission electron microscopy, 27Al MAS NMR, thermogravimetric analysis, and their acid sites are quantified by FTIR spectroscopy of adsorbed basic probe molecules. The catalytic properties of the pristine and modified zeolites are evaluated in the dealkylation of 1,3,5‐triisopropylbenzene. Tuning the etching conditions allows to generate hierarchical zeolites without losing micropore volume. Furthermore, both fluoride etchants do not change the acid properties of the zeolite substantially, which is confirmed by chemical composition analysis (ICP‐OES) and by FTIR spectroscopy of pyridine. The dissolution rate of zeolite L is much faster with NH4HF2 than NH4F. The set of experimental data shows that the 1 wt% NH4HF2 solution is an efficient etchant able to generate mesopores without affecting the parent zeolite properties as lower amounts of fluoride source are required than with concentrated (20–40 wt%) NH4F solutions. [ABSTRACT FROM AUTHOR]

The effect of amorphous aluminosilicate precursor nanoparticles on the formation of nanosized zeolites with faujasite (FAU) and sodalite (SOD) type frameworks is illustrated using a new synthetic strategy to prepare nanosized zeolites with tailored particle size distribution, morphology, and structure. This two‐step synthesis procedure includes the formation of colloidal suspensions followed by separation of the amorphous precursor nanoparticles, and their subsequent transformation into nanosized crystals by treatment with alkali suspensions (NaOH) solutions only. The selective transformation of the amorphous nanoparticles into FAU and SOD nanosized crystals is studied at atomistic and microscopic levels using 29Si and 23Na nuclear magnetic resonanse (NMR) spectroscopy, X‐ray powder diffraction, and N2 physisorption, respectively. The presence of sodalite cages occluding highly mobile sodium in the amorphous nanoparticles is confirmed by 23Na‐1H D‐HMQC NMR spectroscopy. The subsequent treatment of these amorphous precursor particles with aqueous sodium hydroxide illustrates that the cations are not only charge compensators but also inorganic templates stabilizing sodalite cages during the long‐range ordering in the amorphous particles. [ABSTRACT FROM AUTHOR]

BPH-type synthetic aluminosilicate zeolite (Linde Q) nanosheets are synthesized at room temperature without organic structure-directing agents (OSDAs). The BPH nanosheets (7 nm thick, 90 nm across; Si/Al = 1.3) are formed in a colloidal suspension using a mixture of structure-directing cations (Cs+, K+, and Na+). In situ XRD reveals the high stability of the BPH nanosheets up to 500 °C under vacuum (0.021 mbar) due to the presence of Cs+. The high CO2 adsorption capacity (3.78 mmol/g) and stability of the BPH nanosheets open the door for the preparation of oriented thin films and membranes for gas separation applications. [ABSTRACT FROM AUTHOR]

The current energy transition presents many technological challenges, such as the development of highly stable catalysts. Herein, we report a novel "top‐down" synthesis approach for preparation of a single‐site Mo‐containing nanosized ZSM‐5 zeolite which has atomically dispersed framework‐molybdenum homogenously distributed through the zeolite crystals. The introduction of Mo heals most of the native point defects in the zeolite structure resulting in an extremely stable material. The important features of this single‐site Mo‐containing ZSM‐5 zeolite are provided by an in‐depth spectroscopic and microscopic analysis. The material demonstrates superior thermal (up to 1000 °C), hydrothermal (steaming), and catalytic (converting methane to hydrogen and higher hydrocarbons) stability, maintaining the atomically disperse Mo, structural integrity of the zeolite, and preventing the formation of silanols. [ABSTRACT FROM AUTHOR]

The development of catalysts that can operate under exceptionally harsh and unconventional conditions is of critical importance for the transition of the energy and chemicals industries to low‐emission and renewable chemical feedstocks. In this review we will highlight materials and more specifically metal‐containing zeolite catalysts that have been tested under harsh reaction conditions such as high temperature light alkane conversion and biomass valorization. Particular attention will be given to studies that explore the stability and recyclability of metal‐containing zeolite catalysts operating in continuous modes. Metal‐containing zeolites are considered as an important class of catalysts operating outside the comfort zone of current heterogeneous catalytic reactions in both gas and liquid phase reactions. The relationship between the properties of the metal‐containing zeolite and catalytic performance will be explored. [ABSTRACT FROM AUTHOR]

The study reports a simple and potentially universal strategy for post-synthetic engineering of zeolite crystals. Our strategy includes the generation of point defects in zeolite crystals by preliminary etching with oxalic acid, followed by the development of these defects by NH4F etching. Several experimental techniques were used to measure and visualize the zeolite framework dissolution as a function of intrinsic and induced defects. It is revealed that the intrinsic defects lead to the extraction of misoriented nano domains, while those introduced by oxalic acid treatment lead further to the formation of small irregular mesopores. The resultant hierarchical zeolite shows substantially improved mesoporosity, in terms of mesopore volume and spatial distribution, and outstanding micropore acid site accessibility. These samples show superior catalytic performance in the dealkylation of a bulky molecule, 1,3,5-triisopropylbenzene. Our approach highlights the significance of chemically induced extrinsic defects, which make zeolite dissolution go beyond the limits set by the zeolite structure and synthesis chemistry. [ABSTRACT FROM AUTHOR]