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Last site standing: A new generation of hierarchical Pt/H-ZSM-22 zeolites is designed for the efficient processing of upcoming renewable feedstocks. The enhanced accessibility of the active sites is vital for the superior activity and exceptional selectivity in the hydroisomerization of model molecules such as nonadecane and pristane., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

NH 4 F etching is used as an unbiased chemical etching technique to hierarchize commercially available nano-sized ZSM-5 crystals. A structure-function relationship is reported, describing how the introduction of mesoporosity in a microporous ZSM-5 zeolite significantly increases its catalytic performance in (aqueous) n-butanol dehydration. Three parent samples are etched under two severity modes: mild (5 minutes of etching) and harsh (40 minutes of etching). Intrinsic features of the parent ZSM-5's, such as their silanol populations, influence the outcome of the etching procedure. For all materials, crystallinity is unaffected, total pore volume increases while micropore volume is almost constant, and active site accessibility increases. For all materials, etching increases the catalytic activity for n-butanol dehydration. Cofeeding water to n-butanol further increases the stability of all catalysts. Microkinetic modeling reveals that the increased activity is related to a decreased stability of dibutyl ether (DBE), the most abundant surface intermediate. A decreased DBE adsorption energy, due to the increased accessibility of the acid sites, facilitates its desorption. NH 4 F etching, a flexible and easy technique to engineer zeolites' textural properties, does not affect the intrinsic nature and quantity of their active sites, leading to superior catalytic performances. Our results highlight the possibility to further increase the efficiency of zeolite catalysis in biomass conversion processes. [Display omitted] • n-butanol dehydration over crystal engineered ZSM-5 zeolites is studied. • Mild NH 4 F-etching increases both activity and stability. • NH 4 F-etched ZSM-5 crystals show no difference in selectivity. • Microkinetic analysis relates effects of NH 4 F-etching to elementary reaction kinetics. • Cofeeding water increases the stability of ZSM-5 catalysts for alcohol dehydration. [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]

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]

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]

Still, the challenging questions are how to control hydroxyls in zeolites using different synthesis methodologies and how to identify them and relate them to the reactivity of zeolites. Optimizing the combination of alkali metal cations and organic cationic SDAs for obtaining new zeolites will be crucial for controlling the Al site distribution and performance of new zeolite catalysts by controlling the bridged hydroxyls. The ideal crystalline framework of zeolites is perturbed by hydroxyl groups. [Extracted from the article]

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. [ABSTRACT FROM AUTHOR]

Embryonic ZSM-5 zeolites are harvested from clear ZSM-5 precursor solutions after freeze-drying and calcination. These materials are microporous with pore sizes close to those of ZSM-5 zeolites. Due to their partially formed structure, embryonic zeolites do not display a long range order and are XRD amorphous. Their micropores are highly accessible, and resistive to high temperature treatments and the strength of their acid sites is comparable to zeolites. These characteristics give them superior catalytic performances in the conversion of a bulky model molecule, 1,3,5-triisopropylbenzene. [ABSTRACT FROM AUTHOR]

A critical overview of post-synthetic approaches to prepare hierarchical zeolites is presented. Historical methods, as dealumination by steaming and/or acid leaching and desilication in basic solutions, are briefly outlined and compared to a newly developed approach based on bi-fluoride anions. The latter offers the advantage of indiscriminate extraction of silicon and aluminum from zeolite frameworks, while the formers discriminate either Al or Si. The resulting material retains the framework composition and intrinsic acidity of its parent zeolite. Such a route proceeds by eliminating the interfaces between intergrown crystals and preserves only the highly crystalline domains. In addition, the secondary porosity formation does not lead to a substantial increase of external surface area and deposition of extra framework species. [ABSTRACT FROM AUTHOR]

This study reports the seeded synthesis of MFI‐type (ZSM‐5) zeolite in fluoride medium at pH = 8.5. Crystal growth kinetics of the resulting zeolite (ZSM‐5‐F) as a function of seed content and crystallization temperature is studied. The crystallization time is reduced to 1.5 h and crystals with sizes below 200 nm and a Si/Al ratio of 23.6 are obtained. A zeolite with similar characteristics but synthesized in a hydroxyl medium (ZSM‐5‐OH) is used to evaluate ZSM‐5s synthesized in different crystallization media. Their physicochemical properties are compared and particular attention is paid to the nature, number, and distribution of silanol sites. The two zeolites exhibit similar number of Brφnsted acid sites; however the material synthesized in a hydroxyl medium contains a substantially larger number of surface and internal silanols that impact significantly its catalytic performance in methanol to hydrocarbon transformation. While the two materials exhibit similar selectivity in methanol transformations, the catalyst synthesized in fluoride medium shows superior activity and resistance to deactivation. The results suggest that seeded synthesis in a fluoride medium can be used for the preparation of superior zeolite catalysts. [ABSTRACT FROM AUTHOR]

Abstract: New techniques and methodologies in the spectroscopic characterization of zeolites provide new insights on the complexity of zeolitic materials. In particular, emerging IR and NMR techniques shed new lights on old problems such as acidity. New, rich and quantitative information can be gathered. In particular, the ability to work under the so-called operando conditions yields much valuable data to rationally design better catalysts or zeolite based materials. The work and inspiration of Eric Derouane are often at the core of this new knowledge. [Copyright &y& Elsevier]

Chemical interactions occurring between zeolites and alumina binders during the critical steps of catalyst forming are the focus of this study. Three widely used and commercially significant variants of FAU zeolite, covering a wide range of Si/Al ratios, micro- and meso-porosity and acidic properties (Y [LZY-64, Si/Al = 2.3] and USY [CBV 720 and CBV 760 with Si/Al = 16 and Si/Al = 28, respectively]) were shaped by extrusion with pseudoboehmite to produce bound extrudates. These extrudates were characterized by conventional techniques (XRD, 27Al NMR and IR spectroscopy, N 2 physisorption ...) and compared to their parent powders activated under the same conditions. The catalytic performances of the zeolite powders, their derived alumina extrudates and physical zeolite/γ-Al 2 O 3 mixtures were also evaluated employing two different reactions: i) n-octane hydroisomerization, to probe all catalytic sites and ii) 1,3,5 tri-isopropyl benzene dealkylation to probe only the external/mesoporous surfaces. The bound zeolites systematically displayed catalytic performance superior to their parent powders or physical mixtures, especially in the dealkylation of 1,3,5 tri-isopropyl benzene. Infrared spectroscopy measurements of the number, nature and strength of the acid sites were consistent with these catalytic results demonstrating that new catalytic sites are created and located on the external or mesoporous surface of the zeolites, i.e. at the zeolite-binder interface. The work reported here clearly illustrates that binding and subsequent thermal treatment of zeolite powders to produce commercially representative forms can significantly alter the quality and quantity of active sites creating active centers not usually present in pure powders which are typically studied and reported in much of the open literature. Such a study is also a blueprint for other catalytic phases, other forming processes (spray-drying, oil-dropping, pelletizing ...) and could also be applied to the shaping of adsorbents. Image 1 • Zeolite Y were shaped by extrusion using pseudoboehmite as binder. • Acidic properties of zeolite extrudates were probed using basic probe molecule and monitored by infrared. • Zeolite shaping alter qualitatively and quantitatively the acidic properties of the final compounds. • Zeolite Y extrudates systematically displayed catalytic performance superior to their parent powders or physical mixtures, especially in the dealkylation of 1,3,5 tri-isopropyl benzene. • New acid sites are formed during shaping, reminiscent of amorphous silica-alumina. [ABSTRACT FROM AUTHOR]

[Display omitted] • On methane dearomatization reaction, two main deactivation modes occurs. • Irreversible damage by zeolite amorphization during the isothermal pre-treatment. • Reversible deactivation by coke deposition ("soft", "hard" and carbide species). • 3 descriptors : coke level, micropore volume loss, monoclinic/orthorhombic change. We report a detailed kinetic study of methane dehydroaromatization on three bifunctional Mo/HZSM-5 catalysts (0.9 wt%, 2.7 wt%, and 17.2 wt% Mo). Two main deactivation modes are present: (i) irreversible damage by zeolite amorphization during the isothermal pre-treatment in an inert atmosphere and (ii) reversible deactivation by coke deposition ("soft", "hard" and carbide species). The former occurs at high Mo loading (>4.0 w%) and provides low activity catalysts. Catalysts with a lower and well-balanced molybdenum loading (<4 w%) suffer mainly from the second deactivation mode. The catalyst decay is modelled by semi-empirical laws including time on stream and coke level. The latter initiates textural and structural catalyst modifications leading to an activity loss. Three deactivation descriptors, 1 : coke level on the spent samples, 2: loss of micropore volume, and 3: monoclinic/orthorhombic phase transition of the zeolite are identified. Further characterization indicates that both molybdenum and carbon species are responsible for the catalytic deactivation of well-balanced catalysts. At least 50% of the initially dispersed molybdenum migrates to the external surface of the zeolite to form large clusters of molybdenum carbide. The coke extracted from the zeolite micropores are confirmed to be mainly unsubstituted polyaromatics. [ABSTRACT FROM AUTHOR]

Abstract: The improvement of molecular transport properties of hierarchical H-ZSM-5 obtained by desilication was evidenced by studying the desorption of o-xylene and isooctane by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). This technique enabled monitoring simultaneously bands associated with the molecular probes and the zeolite, using powdered sample masses as low as 1mg. Two H-ZSM-5 samples with markedly different crystal sizes were investigated. The first sample was commercial and consisted of small crystallites (ca. 250nm). The second sample were laboratory-made large crystals with coffin-like shape (ca. 17×4×4μm3). The hierarchical derivatives of the small and large zeolite crystals displayed 250 and 120m2 g−1 of mesopore surface area, respectively, in contrast to the 62 and 5m2 g−1 of the parent counterparts. The data based on o-xylene desorption were partly disguised by site-desorption limitations. Desorption experiments using isooctane evidenced a 4-fold reduction in the characteristic diffusion path length on both mesoporous small and large zeolites with respect to their purely microporous analogues. These results confirm the substantial potential for improvement of commercial nanocrystalline zeolites in diffusion-limited reactions upon the introduction of intra-crystalline mesoporosity by post-synthesis modification. [Copyright &y& Elsevier]

• Wet ball milling of -COK-14 zeolite in presence of a dissolved Al source. • Particle size reduction and framework aluminum introduction result from milling. • Milled and aluminated COK-14 contains Brønsted acid sites. • Milled and aluminated COK-14 loaded with platina is an ideal bifunctional catalyst. The precursor of all-silica COK-14 zeolite (OKO topology) with interrupted framework was subjected to wet ball milling in the presence of aluminum isopropoxide. Alumination and particle size reduction of the zeolite crystals was combined in this way. Wet ball milling resulted in fragmentation of the platelet-shape COK-14 crystals while preserving crystallinity. 27Al NMR spectroscopy of the fully condensed COK-14 zeolite, obtained by calcination of milled -COK-14 precursor, confirmed the incorporation of tetrahedrally coordinated Al atoms in the framework. The creation of Brønsted acid sites was confirmed by pyridine adsorption. Loaded with platinum, the sample showed ideal bifunctional catalytic behavior in hydroisomerization and hydrocracking of n -decane model alkane compound. Aluminum incorporation by milling is an alternative to the atomic layer deposition (ALD) process using trimethylaluminum and to thermal alumination. Wet ball milling in presence of aluminum isopropoxide shows great potential for making siliceous zeolites catalytically active. [ABSTRACT FROM AUTHOR]

A series of ZSM-5 zeolites (embryonic, microporous, hierarchical) is studied in the catalytic cracking of polypropylene in the framework of its chemical recycling. Two important zeolite features impact their catalytic performances and allow their design as efficient catalysts: porosity and acidity. They also play a key role in catalyst deactivation and regeneration. A detailed thermogravimetric and spectroscopic (operando FT-IR) analysis of the reaction, including catalyst coking and regeneration, shows the emergence of rules to design fit-for-purpose catalysts to be used in existing or grass-roots FCC units. [Display omitted] • Operando FT-IR-GC-MS study highlights the relative role of the micro- & mesoporous surfaces. • Complementary roles in PP cracking: porosity and acid site strength related to confinement. • Reversible embryonic zeolites deactivation makes PP recycling to fuel or petrochemicals. • The rules to design fit-for-purpose catalysts to be used in existing or grass-roots FCC units. [ABSTRACT FROM AUTHOR]

[Display omitted] • Smaller discrete crystallites of meshed K-CHA improves dynamic adsorption performance. • Nano-sized K-CHA has sharper CO 2 breakthrough, reaches equilibrium more rapidly. • Improved utilisation of fixed-bed for CO 2 separation using nano-sized K-CHA. • Reduced discrete crystallite size increases the mesoporosity of the adsorbent particle. • Nano-sized K-CHA exhibits fewer CO 2 chemisorbed species than micron-sized K-CHA. The performance of K-CHA nanozeolite composed of discrete nanoparticles prepared by an organic template-free direct synthesis is compared to that of conventional micron-sized K-CHA with an order of magnitude difference in particle size and identical chemical composition (Si/Al ratio and cations) for the separation of dilute CO 2 from N 2. Breakthrough curve analysis of the zeolites meshed to identical sizes demonstrates the superior performance of nanozeolites for gas separation due to the significantly faster diffusion of CO 2 molecules through the bed composed of meshed nanozeolite particles evidenced by the enhanced mass transfer, more rapid establishment of equilibrium, and faster desorption of CO 2. Modelling of the CO 2 breakthrough curves indicates enhanced mass transfer properties of the CHA nanozeolite due to the higher linear driving force parameter values. Variation of the modelling parameters and back-calculation of the diffusion coefficients indicates that axial diffusion contributes significantly to the mass transfer behaviour, yet also reveals significantly lower micropore diffusion resistance for the nano-sized K-CHA. These results demonstrate for rapid kinetically controlled sorption-based separations, that by reducing the size of the discrete crystallites of the meshed adsorbent particle by an order of magnitude, significant improvements in the utilization of the bed can be achieved due to the shortening of the mass-transfer zone, improving the separation performance. [ABSTRACT FROM AUTHOR]

There is an increasing demand for porous materials able to separate the components of natural gas, mainly CH 4 and CO 2. Flexible small pore zeolites are interesting candidates due to their high sorption capacity and ability to selectively separate molecules of similar sizes. This selectivity comes from their small pores, large cavities, and pore shapes which can be controlled by the introduction of different extra-framework cations such as Na+, K+, Cs+. Furthermore, the extra-framework cations selectively provide access to the pores and cages of the zeolite depending on the nature of the molecules present. The strategy to prepare CHA-type zeolites across a range of particle sizes, from micron-sized dimensions to nanocrystals with a size of 50 nm, was investigated. The quantities of extra-framework cations and the hydrothermal conditions were optimised in order to avoid the formation of secondary structural phases and selectively target the CHA phase. The CHA-type zeolites were characterised by electron microscopy, elemental analysis, MAS NMR and FTIR spectroscopy, and PXRD. The Si/Al ratio of the obtained CHA zeolite was between 1.7 and 2.6 which is ideal for gas separation applications. The nanosized as-synthesised CHA zeolite (Si/Al = 2.4) demonstrates a high CO 2 storage capacity (4.6 mmol/g) making it an ideal candidate for gas separation applications. [Display omitted] • Strategy to prepare CHA type zeolites across a range of particle sizes. • Phase transition in template free precursors. • Monodispersed nanosized CHA zeolite samples with a Si/Al ratio of 2.4. • CO 2 storage capacity of CHA zeolite. [ABSTRACT FROM AUTHOR]

The study reports a novel catalyst based on supported molybdenum-carbide (Mo 2 C) phase for oxidative dehydrogenation of ethane with CO 2 (ODH-CO 2). The optimal result is obtained with MoS 2 -precursor as the intermediate supported on a non-acidic embryonic zeolite, which is transformed in situ to Mo 2 C (Mo 2 C@EZ). The ultimate catalyst and its intermediates are characterized. 66% conversion of ethane, 58% of ethylene yield, and 56% conversion of CO 2 to CO with the in situ co-produced hydrogen obtained from ethane to ethylene transformation are the achievements of utilizing Mo 2 C@EZ. The performed techno-economic study on Mo 2 C@EZ results in a potentially CO 2 negative route for ethylene production with 109% of CO 2 reduction per ton of produced ethylene in comparison with a conventional ethane cracker. The process is expected to be cheaper in capital expenditure (CAPEX) and operating expenses (OPEX) thanks to a simpler product slate, lower energy demand, and no requirement for steam dilution. [Display omitted] • Embryonic zeolite supported Mo 2 C catalyst is prepared and comprehensively characterized. • The catalyst is employed for oxidative dehydrogenation of ethane with CO 2 (ODH-CO 2). • The proposed catalyst allows designing a potentially CO 2 negative technology. • 109% of CO 2 reduction in comparison to state-of-the-art ethane cracker is achieved. • A technico-economical analysis of the proposed ODH-CO 2 process is performed. [ABSTRACT FROM AUTHOR]

The impact of the textural properties of H-ZSM-5 zeolites in the conversion of ethanol to hydrocarbons at 623 K and under 3.0 MPa pressure is investigated. We highlight that the lifetime of the catalysts is not correlated to the coking rate but to the number of pore mouths. The addition of macropores (fluoride leaching) or mesopores (alkaline leaching) to micron-sized zeolites is a simple approach to increase the number of pore mouths and reduce the diffusion path length of molecules in the micropores. However, the most efficient way is to reduce the zeolite crystal size to nanometers. The longest catalyst lifetime ( > 100 h) is obtained with a hierarchical nanometer-sized zeolite even though most of its acid sites are poisoned. The important impact of the nature of coke on the catalysts regeneration is also highlighted. [ABSTRACT FROM AUTHOR]

FER-type zeolites were synthesized in the presence of Na-Ethylendiamine (Na–En), Na–Pyrrolidine (Na–Py) and Na–K. The crystallization times varied between 96 and 240 h. Ferrierite harvested from the Na–En synthesis was also used as seeds and reduced crystallization time from 240 to 30 h. The product of seeded synthesis was not uniform: nanosized with micronsized crystals as well as complex aggregates of different sizes were obtained. Hierarchical FER-type zeolites were prepared using seeded Na–En synthesized FER as a parent. Secondary pores in zeolite crystals were formed by etching at room temperature with HF-NH 4 F containing solutions, using the HF concentration and treatment time as variables. Crystal morphology and physicochemical characteristics of micron-, nano-sized and hierarchical FER-type crystals were studied by complementary methods including: X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG/dTG), 27 Al and 29 Si MAS NMR, IR spectroscopy of adsorbed probe molecules (Pyridine, Acetonitrile and Lutidine), nitrogen adsorption and chemical analysis. We demonstrate that FER-type zeolites with pre-determined properties can be easily prepared. [ABSTRACT FROM AUTHOR]

The accessibility to sodalite (SOD) cages in nanosized zeolite X (FAU-type framework) is tuned by varying the nature and location of extra-framework exchangeable cations (Na+, Li+, Cs+, K+ and Rb+). Hyperpolarized (HP) and EXchange SpectroscopY (EXSY) 129Xe NMR experiments highlight the connectivity between SOD- and super (SUP)-cages, in particular that its diffusion pathway from sodalites to supercages depends mainly on the size and location of extra-framework cations present in the zeolite. These 129Xe NMR results are supported by DFT simulations. Based on the computed adsorption energies of Xe in both SOD and SUP cages of zeolite X with different cationic compositions, it is concluded that xenon penetration in SUP cages is always favorable while the adsorption in the SOD cages is possible only if small cations (Na+, Li+, K+) are present. [Display omitted] • The accessibility to sodalite cages in nanosized zeolite X is tuned by varying the nature and location of extra-framework cations. • Hyperpolarized 129Xe NMR experiments highlight the connectivity between sodalite and supercages. • Accommodation of Xe in supercages is always favorable while sodalite cages are only accessible when small cations are present. [ABSTRACT FROM AUTHOR]

Highlights: [•] Hierarchization of ZSM-22 favors hydroisomerization and limits hydrocracking [•] Hierarchical ZSM-22 has lower acidity in micropores and higher acidity in pore mouths [•] Branching occurs in pore mouths; hydrocracking in pore mouths and micropores [•] Hierarchization is a unique tool to design superior hydroisomerization catalysts [•] Pristane is a convenient model molecule for probing pore mouth catalysis [Copyright &y& Elsevier]

An accessibility index (ACI) was derived from infrared spectroscopy of substituted alkylpyridines with different size (pyridine: 0.57nm, 2,6-lutidine: 0.67nm, and 2,4,6-collidine: 0.74nm) over hierarchical porous ZSM-5 crystals. The samples were prepared by selective silicon extraction of a commercial sample in NaOH (desilication), and they contained different degrees of intracrystalline mesoporosity. Our results demonstrate the enhanced accessibility of Brønsted acid sites in the hierarchical zeolites. For example, a relatively bulky molecule such as collidine, which probes practically no acid site of the parent medium-pore MFI structure, can access up to 40% of the acid sites in the mesoporous sample. The ACI is a powerful tool to standardize acid site accessibility in zeolites, and can be used to rank the effectiveness of synthetic strategies to prepare hierarchical zeolites. [Copyright &y& Elsevier]

A technique for the quantitative determination of adsorbed species on zeolites and other solids was designed by coupling infrared spectroscopy and in situ thermogravimetry. The weight of H-Y zeolites in an infrared spectrometer was monitored upon pyridine adsorption by a McBain type microbalance. Improved extinction coefficients for the pyridinium band and for ν(OH) bands were determined on these reference materials. The influence of the temperature used for desorption of physisorbed pyridine was studied. [Copyright &y& Elsevier]

Cumene conversion under an excess of benzene is studied over a series of mordenite (MOR) zeolites (Na-MOR, HNa-MOR, H-MOR and dealuminated H-MOR) by in situ 13C and 1H MAS NMR spectroscopy in the temperature range 298–473 K. By tracing the fate of 13C labeled atoms in the benzene molecule, intermolecular transalkylation, disproportionation and isomerization reactions are highlighted. The reactivity of MOR-based catalysts in these reactions is found to increase in the following order: Na-MOR. Transalkylation and disproportionation require mild conditions (T=298–393 K, weak acidity), while isomerization to n-propylbenzene needs more severe conditions (T>473 K, strong acid sites). The reaction mechanisms are discussed. [Copyright &y& Elsevier]

• The use of FER as catalyst for the dehydration of iso-butanol results in an excellent selectivity for n-butenes. • The external Brønsted acid sites function as isobutanol dehydration active sites. • High external Brønsted acidity improves selectivity to n-butenes. • Use of in-situ and operando characterisation toolboxes allowed identifying the active sites. The conversion of isobutanol to light olefins over zeolites was investigated by IR operando spectroscopy. FER zeolites showed a surprisingly high selectivity for the direct conversion of iso-butanol to linear butenes, hence catalyzing dehydration and skeletal isomerization in one step. As a fundamental understanding of the separate reactions is required to design superior catalysts, an in-situ and operando FT-IR mechanistic study of the reaction was carried out. The spectroscopic data, the derived species participating and their respective role are analyzed using chemometric (PCA and MCR-ALS) tools. We highlighted the role played by the external acid sites and the requirement of a specific distance between these sites to ensure the n-butene selectivity and point that the internal Brønsted acidity has an adverse effect on the catalyst stability. Moreover, there is no correlation between the carbon species formed on the surface and the exceptional selectivity towards n-butenes, allowing to exclude a "carbon pool" mechanism. [ABSTRACT FROM AUTHOR]

NH 4 -SSZ-13 is etched with an aqueous solution of 40 w /% NH 4 F under different time/temperature conditions to obtain hierarchical derivatives. The etched zeolites are characterized by XRD, SEM, N 2 physisorption, 29Si/27Al/19F MAS NMR, ICP-AES, and their acidity monitored by in situ FTIR spectroscopy using acetonitrile as a probe molecule. The results highlight that the zeolite is very sensitive to high temperature and high liquid-solid ratio treatments leading to substantial crystallinity losses. These two parameters need careful tuning to obtain hierarchical derivatives retaining important characteristics as micropore volume and framework Si/Al ratio. The catalytic activity of the modified SSZ-13 is evaluated in the n-propanol conversion. Image 1 • Zeolite SSZ-13 (CHA-type) is subjected to chemical etching in an aqueous NH 4 F solution to introduce mesopores. • The hierarchical zeolite preserved the parent zeolite properties in terms of framework composition and Brønsted acidity. • The obtained SSZ-13 derivatives show higher coke contents but slower deactivation in the dehydration of n-propanol. [ABSTRACT FROM AUTHOR]

The texture and acidity of a parent synthetic erionite zeolite (ERI structure) are modified by a two-step top-down treatment involving acid (HNO 3) and base (NaOH) biased leaching as well as an unbiased HF/NH 4 F leaching. These zeolites are compared to a bottom-up prepared nanosized ERI, UZM-12. The structural (XRD, 29Si MAS NMR), textural (N 2 adsorption-desorption, STEM) and acidic (FT-IR spectroscopy of adsorbed probe molecules) properties of the parent and hierarchical ERI are also carefully monitored. Among all top-down hierarchization strategies applied for 8-ring ERI structure, the sequential leaching in acid (HNO 3) and caustic (NaOH) solutions is the most efficient to add mesoporosity to the native microporosity. The catalytic performances of the hierarchical materials and their parent are assessed in the dealkylation of 1,3,5-triisopropylbenzene (TiPBz); they are in line with the mesoporous external surface area and the external surface acid site density for all samples. The best top-down hierarchical ERI has similar catalytic properties as the nanosized ERI, UZM-12. Image 1 • Synthetic erionite modified by a top-down treatment compared to a bottom-up prepared UZM-12. • Mesoporosity added to the native microporosity by sequential acid/caustic leaching. • Optimized textural and acidic parameters enhances the TiPBz dealkylation. • Best top-down hierarchical ERI has similar catalytic properties as the nanosized UZM-12. [ABSTRACT FROM AUTHOR]